Browsing by Subject "Transfection"

Now showing 1 - 20 of 34

Open Access
A complex intronic enhancer regulates expression of the CFTR gene by direct interaction with the promoter.
(J Cell Mol Med, 2009-04) Ott, Christopher J; Suszko, Magdalena; Blackledge, Neil P; Wright, Jane E; Crawford, Gregory E; Harris, Ann
Genes can maintain spatiotemporal expression patterns by long-range interactions between cis-acting elements. The cystic fibrosis transmembrane conductance regulator gene (CFTR) is expressed primarily in epithelial cells. An element located within a DNase I-hypersensitive site (DHS) 10 kb into the first intron was previously shown to augment CFTR promoter activity in a tissue-specific manner. Here, we reveal the mechanism by which this element influences CFTR transcription. We employed a high-resolution method of mapping DHS using tiled microarrays to accurately locate the intron 1 DHS. Transfection of promoter-reporter constructs demonstrated that the element displays classical tissue-specific enhancer properties and can independently recruit factors necessary for transcription initiation. In vitro DNase I footprinting analysis identified a protected region that corresponds to a conserved, predicted binding site for hepatocyte nuclear factor 1 (HNF1). We demonstrate by electromobility shift assays (EMSA) and chromatin immunoprecipitation (ChIP) that HNF1 binds to this element both in vitro and in vivo. Moreover, using chromosome conformation capture (3C) analysis, we show that this element interacts with the CFTR promoter in CFTR-expressing cells. These data provide the first insight into the three- dimensional (3D) structure of the CFTR locus and confirm the contribution of intronic cis-acting elements to the regulation of CFTR gene expression.
Open Access
A genome-wide RNAi screen reveals multiple regulators of caspase activation.
(The Journal of cell biology, 2007-11-12) Yi, Caroline H; Sogah, Dodzie K; Boyce, Michael; Degterev, Alexei; Christofferson, Dana E; Yuan, Junying
Apoptosis is an evolutionally conserved cellular suicide mechanism that can be activated in response to a variety of stressful stimuli. Increasing evidence suggests that apoptotic regulation relies on specialized cell death signaling pathways and also integrates diverse signals from additional regulatory circuits, including those of cellular homeostasis. We present a genome-wide RNA interference screen to systematically identify regulators of apoptosis induced by DNA damage in Drosophila melanogaster cells. We identify 47 double- stranded RNA that target a functionally diverse set of genes, including several with a known function in promoting cell death. Further characterization uncovers 10 genes that influence caspase activation upon the removal of Drosophila inhibitor of apoptosis 1. This set includes the Drosophila initiator caspase Dronc and, surprisingly, several metabolic regulators, a candidate tumor suppressor, Charlatan, and an N-acetyltransferase, ARD1. Importantly, several of these genes show functional conservation in regulating apoptosis in mammalian cells. Our data suggest a previously unappreciated fundamental connection between various cellular processes and caspase-dependent cell death.
Open Access
AAV Gene Therapy for MPS1-associated Corneal Blindness.
(Scientific reports, 2016-02-22) Vance, Melisa; Llanga, Telmo; Bennett, Will; Woodard, Kenton; Murlidharan, Giridhar; Chungfat, Neil; Asokan, Aravind; Gilger, Brian; Kurtzberg, Joanne; Samulski, R Jude; Hirsch, Matthew L
Although cord blood transplantation has significantly extended the lifespan of mucopolysaccharidosis type 1 (MPS1) patients, over 95% manifest cornea clouding with about 50% progressing to blindness. As corneal transplants are met with high rejection rates in MPS1 children, there remains no treatment to prevent blindness or restore vision in MPS1 children. Since MPS1 is caused by mutations in idua, which encodes alpha-L-iduronidase, a gene addition strategy to prevent, and potentially reverse, MPS1-associated corneal blindness was investigated. Initially, a codon optimized idua cDNA expression cassette (opt-IDUA) was validated for IDUA production and function following adeno-associated virus (AAV) vector transduction of MPS1 patient fibroblasts. Then, an AAV serotype evaluation in human cornea explants identified an AAV8 and 9 chimeric capsid (8G9) as most efficient for transduction. AAV8G9-opt-IDUA administered to human corneas via intrastromal injection demonstrated widespread transduction, which included cells that naturally produce IDUA, and resulted in a >10-fold supraphysiological increase in IDUA activity. No significant apoptosis related to AAV vectors or IDUA was observed under any conditions in both human corneas and MPS1 patient fibroblasts. The collective preclinical data demonstrate safe and efficient IDUA delivery to human corneas, which may prevent and potentially reverse MPS1-associated cornea blindness.
Open Access
Arc/Arg3.1 translation is controlled by convergent N-methyl-D-aspartate and Gs-coupled receptor signaling pathways.
(The Journal of biological chemistry, 2008-01) Bloomer, Wendy AC; VanDongen, Hendrika MA; VanDongen, Antonius MJ
Arc/Arg3.1 is an immediate early gene whose expression is necessary for the late-phase of long-term potentiation (LTP) and memory consolidation. Whereas pathways regulating Arc transcription have been extensively investigated, less is known about the role of post-transcriptional mechanisms in Arc expression. Fluorescence microscopy experiments in cultured hippocampal neurons revealed that Arc protein level was dramatically increased by activation of the cAMP-dependent protein kinase (PKA) pathway, which is implicated in long-term memory. A PKA-dependent increase in Arc protein level was observed after pharmacological or synaptic activation of N-methyl-D-aspartate (NMDA) receptors, which play a critical role in both LTP induction and learning. Arc protein was also up-regulated by activation of PKA through G(s)-coupled dopamine and beta-adrenergic receptors, which regulate the late-phase of LTP and memory. When agonists for the NMDA and G(s)-coupled receptors were co-applied, they had an additive effect on Arc protein expression. Interestingly, G(s)-coupled receptor stimulation was ineffective in the presence of an NMDA receptor antagonist, suggesting calcium influx through the NMDA receptor plays a gating role in this pathway. Stimulation of the cAMP/PKA pathway did not affect Arc mRNA level or protein stability, identifying translational efficacy as the main determinant of Arc protein expression level. It is concluded that efficient Arc translation requires NMDA receptor activity, whereas a further enhancement can be achieved with activation of G(s)-coupled receptors. These experiments have, therefore, revealed remarkable similarities in the signaling pathways that control Arc expression and those that regulate LTP, learning, and memory.
Open Access
beta-Arrestin-mediated PDE4 cAMP phosphodiesterase recruitment regulates beta-adrenoceptor switching from Gs to Gi.
(Proc Natl Acad Sci U S A, 2003-02-04) Baillie, George S; Sood, Arvind; McPhee, Ian; Gall, Irene; Perry, Stephen J; Lefkowitz, Robert J; Houslay, Miles D
Phosphorylation of the beta(2) adrenoreceptor (beta(2)AR) by cAMP-activated protein kinase A (PKA) switches its predominant coupling from stimulatory guanine nucleotide regulatory protein (G(s)) to inhibitory guanine nucleotide regulatory protein (G(i)). beta-Arrestins recruit the cAMP-degrading PDE4 phosphodiesterases to the beta(2)AR, thus controlling PKA activity at the membrane. Here we investigate a role for PDE4 recruitment in regulating G protein switching by the beta(2)AR. In human embryonic kidney 293 cells overexpressing a recombinant beta(2)AR, stimulation with isoprenaline recruits beta-arrestins 1 and 2 as well as both PDE4D3 and PDE4D5 to the receptor and stimulates receptor phosphorylation by PKA. The PKA phosphorylation status of the beta(2)AR is enhanced markedly when cells are treated with the selective PDE4-inhibitor rolipram or when they are transfected with a catalytically inactive PDE4D mutant (PDE4D5-D556A) that competitively inhibits isoprenaline-stimulated recruitment of native PDE4 to the beta(2)AR. Rolipram and PDE4D5-D556A also enhance beta(2)AR-mediated activation of extracellular signal-regulated kinases ERK12. This is consistent with a switch in coupling of the receptor from G(s) to G(i), because the ERK12 activation is sensitive to both inhibitors of PKA (H89) and G(i) (pertussis toxin). In cardiac myocytes, the beta(2)AR also switches from G(s) to G(i) coupling. Treating primary cardiac myocytes with isoprenaline induces recruitment of PDE4D3 and PDE4D5 to membranes and activates ERK12. Rolipram robustly enhances this activation in a manner sensitive to both pertussis toxin and H89. Adenovirus-mediated expression of PDE4D5-D556A also potentiates ERK12 activation. Thus, receptor-stimulated beta-arrestin-mediated recruitment of PDE4 plays a central role in the regulation of G protein switching by the beta(2)AR in a physiological system, the cardiac myocyte.
Restricted
beta2-Adrenergic receptor regulation by GIT1, a G protein-coupled receptor kinase-associated ADP ribosylation factor GTPase-activating protein.
(Proc Natl Acad Sci U S A, 1998-11-24) Premont, RT; Claing, A; Vitale, N; Freeman, JL; Pitcher, JA; Patton, WA; Moss, J; Vaughan, M; Lefkowitz, RJ
G protein-coupled receptor activation leads to the membrane recruitment and activation of G protein-coupled receptor kinases, which phosphorylate receptors and lead to their inactivation. We have identified a novel G protein-coupled receptor kinase-interacting protein, GIT1, that is a GTPase-activating protein (GAP) for the ADP ribosylation factor (ARF) family of small GTP-binding proteins. Overexpression of GIT1 leads to reduced beta2-adrenergic receptor signaling and increased receptor phosphorylation, which result from reduced receptor internalization and resensitization. These cellular effects of GIT1 require its intact ARF GAP activity and do not reflect regulation of GRK kinase activity. These results suggest an essential role for ARF proteins in regulating beta2-adrenergic receptor endocytosis. Moreover, they provide a mechanism for integration of receptor activation and endocytosis through regulation of ARF protein activation by GRK-mediated recruitment of the GIT1 ARF GAP to the plasma membrane.
Open Access
Biologically Improved Electrotransfection for Gene Delivery and Genome Editing
(2019) Mao, Mao
Successful transfection of genetically active materials is essential to gene delivery and genome editing. Electrotransfection, also known as electroporation, is a fast, safe, and convenient non-viral method for introducing materials such as proteins and nucleic acids into cells and tissues. It has been widely used in academic research, industrial manufacturing, and clinical therapeutics. Particularly, electrotransfection is one of the most commonly used method in gene delivery into mammalian cells. However, despite its many advantages comparing to other gene delivery methods, the application of electrotransfection is limited by inconsistent transfection efficiency, which is caused by the poor understanding of the mechanism of electrotransfection.
The goal of my research is to understand the fundamental biological mechanisms of electrotransfection and to develop novel strategies that can improve the transfection efficiency of gene delivery and genome editing. To this end, this study is divided into two phases. Phase 1 aims at understanding the key cellular components involved in the transport process. Phase 2 focuses on the development of strategies to enhance electrotransfection by controlling the biological pathways that are involved in electrotransfection.
In the first phase of my study, we investigated the dependence of electrotransfection efficiency on endocytosis. Data from this study demonstrated that macropinocytosis is involved in electrotransfection. The results revealed that electric pulses induced cell membrane ruffling and actin cytoskeleton remodeling. Using fluorescently labeled pDNA and a macropinocytosis marker (i.e., dextran), the study showed that electrotransfected pDNA co-localized with dextran in intracellular vesicles formed from macropinocytosis. Furthermore, electrotransfection efficiency was reduced significantly by lowering temperature or treatment of cells with a pharmacological inhibitor of Rac1 and could be altered by changing Rac1 activity. Taken together, the findings suggested that electrotransfection of pDNA involved Rac1-dependent macropinocytosis.
Second phase of this study focuses on the intracellular transport of plasmid DNA, especially the transport of DNA molecules towards degradative compartments. Our data elucidated that components in both endocytic and autophagic pathways are responsible for intracellular trafficking and processing of transfected materials such as pDNA. In addition, we also characterized a new type of vesicle named amphisome-like vesicle (ALB) and revealed its involvement in electrotransfection. Based on these findings, we propose a novel strategy to enhance electrotransfection by blocking degradative routes within the endocytic pathways, which led to the development of a new technique called transfection by redirection of endocytic and autophagic traffic (TREAT). Transfection of plasmid DNA (pDNA), messenger RNA (mRNA), sleeping beauty transposon system (SB), and different forms of CRISPR/Cas9 system by TREAT achieved superior efficiency in various cell lines including difficult-to-transfect human primary cells. In addition, we successfully applied TREAT method to improve clinically relevant applications including SB-based gene integration and CRISPR/Cas9-based editing of T cell receptor alpha constant (TRAC). In summary, we studied the biological mechanism of electrotransfection and developed a general, flexible, and reliable technique to enable highly efficient non-viral gene delivery and genome editing. Furthermore, the insights gained on the mechanism of electrotransfection provide better understanding of cellular response to exogenous materials. In the future, our study could potentially pave new paths for a wide range of research and therapeutic applications such as CRISPR/Cas9 mediated high-throughput loss-of-function gene screening analysis, correction of disease-related mutations, as well as genetic engineering of immune cells and stem cells for transplantation.
Open Access
Characterization of the murine BEK fibroblast growth factor (FGF) receptor: activation by three members of the FGF family and requirement for heparin.
(Proc Natl Acad Sci U S A, 1992-04-15) Mansukhani, A; Dell'Era, P; Moscatelli, D; Kornbluth, S; Hanafusa, H; Basilico, C
The bek gene encodes a member of the high-affinity fibroblast growth factor receptor family. The BEK/FGFR-2 receptor is a membrane-spanning tyrosine kinase with the typical features of FGF receptors. We have cloned a murine bek cDNA and expressed it in receptor-negative Chinese hamster ovary cells and in 32D myeloid cells. The BEK receptor expressed in Chinese hamster ovary cells binds acidic FGF, basic FGF, and Kaposi FGF equally well but does not bind keratinocyte growth factor or FGF-5 appreciably. Upon treatment with basic FGF or Kaposi FGF, the BEK receptor is phosphorylated and a mitogenic response is achieved. Heparan sulfate proteoglycans have been shown to play an obligate role in basic FGF binding to the high-affinity FLG receptor. Unlike the BEK-expressing Chinese hamster ovary cells, 32D cells expressing the BEK receptor require the addition of exogenous heparin in order to grow in the presence of basic FGF or Kaposi FGF. We show that the addition of heparin greatly enhances the binding of radio-labeled basic FGF to the receptor. Thus the BEK receptor, like FLG, also requires an interaction with heparan sulfate proteoglycans to facilitate binding to its ligands.
Open Access
Expansion of the alpha 2-adrenergic receptor family: cloning and characterization of a human alpha 2-adrenergic receptor subtype, the gene for which is located on chromosome 2.
(Proc Natl Acad Sci U S A, 1990-07) Lomasney, JW; Lorenz, W; Allen, LF; King, K; Regan, JW; Yang-Feng, TL; Caron, MG; Lefkowitz, RJ
Pharmacologic, biochemical, and genetic analyses have demonstrated the existence of multiple alpha 2-adrenergic receptor (alpha 2AR) subtypes. We have cloned a human alpha 2AR by using the polymerase chain reaction with oligonucleotide primers homologous to conserved regions of the previously cloned alpha 2ARs, the genes for which are located on human chromosomes 4 (C4) and 10 (C10). The deduced amino acid sequence encodes a protein of 450 amino acids whose putative topology is similar to that of the family of guanine nucleotide-binding protein-coupled receptors, but whose structure most closely resembles that of the alpha 2ARs. Competition curve analysis of the binding properties of the receptor expressed in COS-7 cells with a variety of adrenergic ligands demonstrates a unique alpha 2AR pharmacology. Hybridization with somatic cell hybrids shows that the gene for this receptor is located on chromosome 2. Northern blot analysis of various rat tissues shows expression in liver and kidney. The unique pharmacology and tissue localization of this receptor suggest that this is an alpha 2AR subtype not previously identified by classical pharmacological or ligand binding approaches.
Open Access
G protein beta gamma subunits stimulate phosphorylation of Shc adapter protein.
(Proc Natl Acad Sci U S A, 1995-09-26) Touhara, K; Hawes, BE; van Biesen, T; Lefkowitz, RJ
The mechanism of mitogen-activated protein (MAP) kinase activation by pertussis toxin-sensitive Gi-coupled receptors is known to involve the beta gamma subunits of heterotrimeric G proteins (G beta gamma), p21ras activation, and an as-yet-unidentified tyrosine kinase. To investigate the mechanism of G beta gamma-stimulated p21ras activation, G beta gamma-mediated tyrosine phosphorylation was examined by overexpressing G beta gamma or alpha 2-C10 adrenergic receptors (ARs) that couple to Gi in COS-7 cells. Immunoprecipitation of phosphotyrosine-containing proteins revealed a 2- to 3-fold increase in the phosphorylation of two proteins of approximately 50 kDa (designated as p52) in G beta gamma-transfected cells or in alpha 2-C10 AR-transfected cells stimulated with the agonist UK-14304. The latter response was pertussis toxin sensitive. These proteins (p52) were also specifically immunoprecipitated with anti-Shc antibodies and comigrated with two Shc proteins, 46 and 52 kDa. The G beta gamma- or alpha 2-C10 AR-stimulated p52 (Shc) phosphorylation was inhibited by coexpression of the carboxyl terminus of beta-adrenergic receptor kinase (a G beta gamma-binding pleckstrin homology domain peptide) or by the tyrosine kinase inhibitors genistein and herbimycin A, but not by a dominant negative mutant of p21ras. Worthmannin, a specific inhibitor of phosphatidylinositol 3-kinase (PI3K) inhibited phosphorylation of p52 (Shc), implying involvement of PI3K. These results suggest that G beta gamma-stimulated Shc phosphorylation represents an early step in the pathway leading to p21ras activation, similar to the mechanism utilized by growth factor tyrosine kinase receptors.
Open Access
G-protein-coupled receptor genes as protooncogenes: constitutively activating mutation of the alpha 1B-adrenergic receptor enhances mitogenesis and tumorigenicity.
(Proc Natl Acad Sci U S A, 1991-12-15) Allen, LF; Lefkowitz, RJ; Caron, MG; Cotecchia, S
The alpha 1B-adrenergic receptor (alpha 1B-ADR) is a member of the G-protein-coupled family of transmembrane receptors. When transfected into Rat-1 and NIH 3T3 fibroblasts, this receptor induces focus formation in an agonist-dependent manner. Focus-derived, transformed fibroblasts exhibit high levels of functional alpha 1B-ADR expression, demonstrate a catecholamine-induced enhancement in the rate of cellular proliferation, and are tumorigenic when injected into nude mice. Induction of neoplastic transformation by the alpha 1B-ADR, therefore, identifies this normal cellular gene as a protooncogene. Mutational alteration of this receptor can lead to activation of this protooncogene, resulting in an enhanced ability of agonist to induce focus formation with a decreased latency and quantitative increase in transformed foci. In contrast to cells expressing the wild-type alpha 1B-ADR, focus formation in "oncomutant"-expressing cell lines appears constitutively activated with the generation of foci in unstimulated cells. Further, these cell lines exhibit near-maximal rates of proliferation even in the absence of catecholamine supplementation. They also demonstrate an enhanced ability for tumor generation in nude mice with a decreased period of latency compared with cells expressing the wild-type receptor. Thus, the alpha 1B-ADR gene can, when overexpressed and activated, function as an oncogene inducing neoplastic transformation. Mutational alteration of this receptor gene can result in the activation of this protooncogene, enhancing its oncogenic potential. These findings suggest that analogous spontaneously occurring mutations in this class of receptor proteins could play a key role in the induction or progression of neoplastic transformation and atherosclerosis.
Open Access
Gi-biased β2AR signaling links GRK2 upregulation to heart failure.
(Circulation research, 2012-01) Zhu, Weizhong; Petrashevskaya, Natalia; Ren, Shuxun; Zhao, Aizhi; Chakir, Khalid; Gao, Erhe; Chuprun, J Kurt; Wang, Yibin; Talan, Mark; Dorn, Gerald W; Lakatta, Edward G; Koch, Walter J; Feldman, Arthur M; Xiao, Rui-Ping
Rationale
Phosphorylation of β(2)-adrenergic receptor (β(2)AR) by a family of serine/threonine kinases known as G protein-coupled receptor kinase (GRK) and protein kinase A (PKA) is a critical determinant of cardiac function. Upregulation of G protein-coupled receptor kinase 2 (GRK2) is a well-established causal factor of heart failure, but the underlying mechanism is poorly understood.
Objective
We sought to determine the relative contribution of PKA- and GRK-mediated phosphorylation of β(2)AR to the receptor coupling to G(i) signaling that attenuates cardiac reserve and contributes to the pathogenesis of heart failure in response to pressure overload.
Methods and results
Overexpression of GRK2 led to a G(i)-dependent decrease of contractile response to βAR stimulation in cultured mouse cardiomyocytes and in vivo. Importantly, cardiac-specific transgenic overexpression of a mutant β(2)AR lacking PKA phosphorylation sites (PKA-TG) but not the wild-type β(2)AR (WT-TG) or a mutant β(2)AR lacking GRK sites (GRK-TG) led to exaggerated cardiac response to pressure overload, as manifested by markedly exacerbated cardiac maladaptive remodeling and failure and early mortality. Furthermore, inhibition of G(i) signaling with pertussis toxin restores cardiac function in heart failure associated with increased β(2)AR to G(i) coupling induced by removing PKA phosphorylation of the receptor and in GRK2 transgenic mice, indicating that enhanced phosphorylation of β(2)AR by GRK and resultant increase in G(i)-biased β(2)AR signaling play an important role in the development of heart failure.
Conclusions
Our data show that enhanced β(2)AR phosphorylation by GRK, in addition to PKA, leads the receptor to G(i)-biased signaling, which, in turn, contributes to the pathogenesis of heart failure, marking G(i)-biased β(2)AR signaling as a primary event linking upregulation of GRK to cardiac maladaptive remodeling, failure and cardiodepression.
Open Access
HLA-B-associated transcript 3 (Bat3)/Scythe is essential for p300-mediated acetylation of p53.
(Genes Dev, 2007-04-01) Sasaki, Toru; Gan, Eugene C; Wakeham, Andrew; Kornbluth, Sally; Mak, Tak W; Okada, Hitoshi
In response to DNA damage, p53 undergoes post-translational modifications (including acetylation) that are critical for its transcriptional activity. However, the mechanism by which p53 acetylation is regulated is still unclear. Here, we describe an essential role for HLA-B-associated transcript 3 (Bat3)/Scythe in controlling the acetylation of p53 required for DNA damage responses. Depletion of Bat3 from human and mouse cells markedly impairs p53-mediated transactivation of its target genes Puma and p21. Although DNA damage-induced phosphorylation, stabilization, and nuclear accumulation of p53 are not significantly affected by Bat3 depletion, p53 acetylation is almost completely abolished. Bat3 forms a complex with p300, and an increased amount of Bat3 enhances the recruitment of p53 to p300 and facilitates subsequent p53 acetylation. In contrast, Bat3-depleted cells show reduced p53-p300 complex formation and decreased p53 acetylation. Furthermore, consistent with our in vitro findings, thymocytes from Bat3-deficient mice exhibit reduced induction of puma and p21, and are resistant to DNA damage-induced apoptosis in vivo. Our data indicate that Bat3 is a novel and essential regulator of p53-mediated responses to genotoxic stress, and that Bat3 controls DNA damage-induced acetylation of p53.
Open Access
Implicated Role of Endocytosis in the Internalization and Intracellular Transport of Plasmid DNA During Electric Field-Mediated Gene Delivery
(2011) Wu, Mina
Electric field mediated gene delivery (EFMGD) or electrotransfection is a popular, non-viral gene delivery method that has been used in a variety of studies and applications ranging from basic cell biology research to clinical gene therapy. Yet, the mechanism(s) by which electrotransfection facilitates DNA delivery across the cell membrane into the cell and its subsequent intracellular transport across the cytosolic space towards the nucleus have been insufficiently studied and still remain controversial. Understanding these mechanisms and characterizing the intracellular journey of pDNA is important for understanding the physiological barriers of EFMGD within the cell, which can be used to engineer better solutions to overcome these barriers with the ultimate goal of improving the transfection efficiency of this technology.
Conventional thought in the field assumes that such transport modes as diffusion, electrophoresis, and electro-osmosis, which govern the entry of small molecules into cells through electric field-generated transient membrane pores, also apply to electric field-mediated delivery of therapeutic DNA. We propose that electrically-induced gene transfer into cells is governed by an alternative, more active mode of transport that entails the involvement of cellular endocytic processes. It is our hypothesis that pulsed electric field generate these membrane pores which interact with nearby DNA molecules; but that actual DNA translocation across the membrane is driven by endocytosis, which consequently, then, also plays a role in the intracellular transport of the DNA. To this end, we first investigated the dependence of electrotransfection efficiency (eTE) on binding of plasmid DNA (pDNA) to plasma membrane. Binding concentrates DNA molecules in the vicinity of the cell membrane, which should theoretically result in a greater number of DNA-membrane interactions during pulsed electric field, more internalized DNA, and ultimately, higher eTE values. We demonstrated that supplementing the electrotransfection buffer with divalent cations (Ca2+ and Mg2+) is an effective method of promoting pDNA adsorption to the cell membrane. This cation-mediated increase in DNA adsorption to the cellular membrane resulted in a consequent increase in eTE, up to a certain threshold concentration for each cation. To determine the timeframe for completion of pDNA internalization following pulse treatment, trypsin treatment was applied to cells at different timepoints after electrotransfection to strip off any residual, membrane-bound pDNA that had not been internalized. Trypsin treatment at 10 min post electrotransfection still resulted in a significant reduction in eTE, indicating that the time period for complete cellular uptake far exceeded the lifetime (~ 10 msec) of electric field-induced transient pores. The role of endocytosis was further probed by noting the effect on eTE when cells were treated with three endocytic inhibitors (chlorpromazine, genistein, dynasore) targeting different internalization mechanisms or silenced of dynamin expression using specific, small interfering RNA (siRNA). siRNA silencing and all three pharmacological inhibitors yielded substantial and statistically significant reductions in the eTE. Taken together, these findings suggest that the mechanism of electric-field mediated DNA internalization entails: (i) binding of pDNA to cell membrane and (ii) endocytosis of membrane-bound pDNA.
The same strategies of pharmacological endocytic inhibition and siRNA silencing was used to further explore and compare electric field-induced pDNA internalization in additional cell lines that differ in terms of cell type, proliferation rates, proliferative capacity (i.e. primary versus immortalized/cancer line), etc. in order to determine whether endocytosis is a universally implicated mechanism across many cell lines. Results showed different endocytic pathways to be recruited for pDNA uptake in a cell-dependent manner and that one or multiple pathways may contribute to uptake within a cell line.
Taken together, the studies presented in this dissertation provide both indirect and direct evidence suggesting an endocytic role in the translocation of pDNA across the cell membrane and its intracellular routing towards the nucleus for EFMGD. These seminal findings could potentially lead to better understanding of the intracellular barriers encountered by EFMGD, more strategic optimization of electrotransfection parameters than the trial-and-error approach currently used, and enhanced transfection efficiencies.
Open Access
Involvement of tyrosine residues located in the carboxyl tail of the human beta 2-adrenergic receptor in agonist-induced down-regulation of the receptor.
(Proc Natl Acad Sci U S A, 1990-07) Valiquette, M; Bonin, H; Hnatowich, M; Caron, MG; Lefkowitz, RJ; Bouvier, M
Chronic exposure of various cell types to adrenergic agonists leads to a decrease in cell surface beta 2-adrenergic receptor (beta 2AR) number. Sequestration of the receptor away from the cell surface as well as a down-regulation of the total number of cellular receptors are believed to contribute to this agonist-mediated regulation of receptor number. However, the molecular mechanisms underlying these phenomena are not well characterized. Recently, tyrosine residues located in the cytoplasmic tails of several membrane receptors, such as the low density lipoprotein and mannose-6-phosphate receptors, have been suggested as playing an important role in the agonist-induced internalization of these receptors. Accordingly, we assessed the potential role of two tyrosine residues in the carboxyl tail of the human beta 2AR in agonist-induced sequestration and down-regulation of the receptor. Tyr-350 and Tyr-354 of the human beta 2AR were replaced with alanine residues by site-directed mutagenesis and both wild-type and mutant beta 2AR were stably expressed in transformed Chinese hamster fibroblasts. The mutation dramatically decreased the ability of the beta 2AR to undergo isoproterenol-induced down-regulation. However, the substitution of Tyr-350 and Tyr-354 did not affect agonist-induced sequestration of the receptor. These results suggest that tyrosine residues in the cytoplasmic tail of human beta 2AR are crucial determinants involved in its down-regulation.
Open Access
Junctophilin-2 expression silencing causes cardiocyte hypertrophy and abnormal intracellular calcium-handling.
(Circulation. Heart failure, 2011-03) Landstrom, AP; Kellen, CA; Dixit, SS; Van Oort, RJ; Garbino, A; Weisleder, N; Ma, J; Wehrens, XHT; Ackerman, MJ
Junctophilin-2 (JPH2), a protein expressed in the junctional membrane complex, is necessary for proper intracellular calcium (Ca(2+)) signaling in cardiac myocytes. Downregulation of JPH2 expression in a model of cardiac hypertrophy was recently associated with defective coupling between plasmalemmal L-type Ca(2+) channels and sarcoplasmic reticular ryanodine receptors. However, it remains unclear whether JPH2 expression is altered in patients with hypertrophic cardiomyopathy (HCM). In addition, the effects of downregulation of JPH2 expression on intracellular Ca(2+) handling are presently poorly understood. We sought to determine whether loss of JPH2 expression is noted among patients with HCM and whether expression silencing might perturb Ca(2+) handling in a prohypertrophic manner.JPH2 expression was reduced in flash-frozen human cardiac tissue procured from patients with HCM compared with ostensibly healthy traumatic death victims. Partial silencing of JPH2 expression in HL-1 cells by a small interfering RNA probe targeted to murine JPH2 mRNA (shJPH2) resulted in myocyte hypertrophy and increased expression of known markers of cardiac hypertrophy. Whereas expression levels of major Ca(2+)-handling proteins were unchanged, shJPH2 cells demonstrated depressed maximal Ca(2+) transient amplitudes that were insensitive to L-type Ca(2+) channel activation with JPH2 knockdown. Further, reduced caffeine-triggered sarcoplasmic reticulum store Ca(2+) levels were observed with potentially increased total Ca(2+) stores. Spontaneous Ca(2+) oscillations were elicited at a higher extracellular [Ca(2+)] and with decreased frequency in JPH2 knockdown cells.Our results show that JPH2 levels are reduced in patients with HCM. Reduced JPH2 expression results in reduced excitation-contraction coupling gain as well as altered Ca(2+) homeostasis, which may be associated with prohypertrophic remodeling.
Open Access
Kalirin promotes neointimal hyperplasia by activating Rac in smooth muscle cells.
(Arteriosclerosis, thrombosis, and vascular biology, 2013-04) Wu, Jiao-Hui; Fanaroff, Alexander C; Sharma, Krishn C; Smith, Liisa S; Brian, Leigh; Eipper, Betty A; Mains, Richard E; Freedman, Neil J; Zhang, Lisheng
Objective
Kalirin is a multifunctional protein that contains 2 guanine nucleotide exchange factor domains for the GTPases Rac1 and RhoA. Variants of KALRN have been associated with atherosclerosis in humans, but Kalirin's activity has been characterized almost exclusively in the central nervous system. We therefore tested the hypothesis that Kalirin functions as a Rho-guanine nucleotide exchange factor in arterial smooth muscle cells (SMCs).
Approach and results
Kalirin-9 protein is expressed abundantly in aorta and bone marrow, as well as in cultured SMCs, endothelial cells, and macrophages. Moreover, arterial Kalirin was upregulated during early atherogenesis in apolipoprotein E-deficient mice. In cultured SMCs, signaling was affected similarly in 3 models of Kalirin loss-of-function: heterozygous Kalrn deletion, Kalirin RNAi, and treatment with the Kalirin Rho-guanine nucleotide exchange factor -1 inhibitor 1-(3-nitrophenyl)-1H-pyrrole-2,5-dione. With reduced Kalirin function, SMCs showed normal RhoA activation but diminished Rac1 activation, assessed as reduced Rac-GTP levels, p21-activated kinase autophosphorylation, and SMC migration. Kalrn(-/+) SMCs proliferated 30% less rapidly than wild-type SMCs. Neointimal hyperplasia engendered by carotid endothelial denudation was ≈60% less in Kalrn(-/+) and SMC-specific Kalrn(-/+) mice than in control mice.
Conclusions
Kalirin functions as a guanine nucleotide exchange factor for Rac1 in SMCs, and promotes SMC migration and proliferation both in vitro and in vivo.
Open Access
KIR polymorphisms modulate peptide-dependent binding to an MHC class I ligand with a Bw6 motif.
(PLoS pathogens, 2011-03) Colantonio, Arnaud D; Bimber, Benjamin N; Neidermyer, William J; Reeves, R Keith; Alter, Galit; Altfeld, Marcus; Johnson, R Paul; Carrington, Mary; O'Connor, David H; Evans, David T
Molecular interactions between killer immunoglobulin-like receptors (KIRs) and their MHC class I ligands play a central role in the regulation of natural killer (NK) cell responses to viral pathogens and tumors. Here we identify Mamu-A1*00201 (Mamu-A*02), a common MHC class I molecule in the rhesus macaque with a canonical Bw6 motif, as a ligand for Mamu-KIR3DL05. Mamu-A1*00201 tetramers folded with certain SIV peptides, but not others, directly stained primary NK cells and Jurkat cells expressing multiple allotypes of Mamu-KIR3DL05. Differences in binding avidity were associated with polymorphisms in the D0 and D1 domains of Mamu-KIR3DL05, whereas differences in peptide-selectivity mapped to the D1 domain. The reciprocal exchange of the third predicted MHC class I-contact loop of the D1 domain switched the specificity of two Mamu-KIR3DL05 allotypes for different Mamu-A1*00201-peptide complexes. Consistent with the function of an inhibitory KIR, incubation of lymphocytes from Mamu-KIR3DL05(+) macaques with target cells expressing Mamu-A1*00201 suppressed the degranulation of tetramer-positive NK cells. These observations reveal a previously unappreciated role for D1 polymorphisms in determining the selectivity of KIRs for MHC class I-bound peptides, and identify the first functional KIR-MHC class I interaction in the rhesus macaque. The modulation of KIR-MHC class I interactions by viral peptides has important implications to pathogenesis, since it suggests that the immunodeficiency viruses, and potentially other types of viruses and tumors, may acquire changes in epitopes that increase the affinity of certain MHC class I ligands for inhibitory KIRs to prevent the activation of specific NK cell subsets.
Open Access
Mammalian genes induce partially reprogrammed pluripotent stem cells in non-mammalian vertebrate and invertebrate species.
(Elife, 2013-09-03) Rosselló, Ricardo Antonio; Chen, Chun-Chun; Dai, Rui; Howard, Jason T; Hochgeschwender, Ute; Jarvis, Erich D
Cells are fundamental units of life, but little is known about evolution of cell states. Induced pluripotent stem cells (iPSCs) are once differentiated cells that have been re-programmed to an embryonic stem cell-like state, providing a powerful platform for biology and medicine. However, they have been limited to a few mammalian species. Here we found that a set of four mammalian transcription factor genes used to generate iPSCs in mouse and humans can induce a partially reprogrammed pluripotent stem cell (PRPSCs) state in vertebrate and invertebrate model organisms, in mammals, birds, fish, and fly, which span 550 million years from a common ancestor. These findings are one of the first to show cross-lineage stem cell-like induction, and to generate pluripotent-like cells for several of these species with in vivo chimeras. We suggest that the stem-cell state may be highly conserved across a wide phylogenetic range. DOI:http://dx.doi.org/10.7554/eLife.00036.001.
Open Access
Membrane binding of plasmid DNA and endocytic pathways are involved in electrotransfection of mammalian cells.
(PLoS One, 2011) Wu, Mina; Yuan, Fan
Electric field mediated gene delivery or electrotransfection is a widely used method in various studies ranging from basic cell biology research to clinical gene therapy. Yet, mechanisms of electrotransfection are still controversial. To this end, we investigated the dependence of electrotransfection efficiency (eTE) on binding of plasmid DNA (pDNA) to plasma membrane and how treatment of cells with three endocytic inhibitors (chlorpromazine, genistein, dynasore) or silencing of dynamin expression with specific, small interfering RNA (siRNA) would affect the eTE. Our data demonstrated that the presence of divalent cations (Ca(2+) and Mg(2+)) in electrotransfection buffer enhanced pDNA adsorption to cell membrane and consequently, this enhanced adsorption led to an increase in eTE, up to a certain threshold concentration for each cation. Trypsin treatment of cells at 10 min post electrotransfection stripped off membrane-bound pDNA and resulted in a significant reduction in eTE, indicating that the time period for complete cellular uptake of pDNA (between 10 and 40 min) far exceeded the lifetime of electric field-induced transient pores (∼10 msec) in the cell membrane. Furthermore, treatment of cells with the siRNA and all three pharmacological inhibitors yielded substantial and statistically significant reductions in the eTE. These findings suggest that electrotransfection depends on two mechanisms: (i) binding of pDNA to cell membrane and (ii) endocytosis of membrane-bound pDNA.

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