Browsing by Subject "HSF1"

Heat Shock transcription Factor 1 (HSF1) has long been recognized as the master regulator and signal integrator in the eukaryotic proteotoxic stress response. Revealed by recent discoveries in cancer, the functions of HSF1 have extended far beyond its canonical role in protein folding, further encompassing critical functions in anti-apoptosis, invasion and metastasis, energy metabolism, DNA damage repair, and evasion of host immune surveillance. Meanwhile, both our understanding of the molecular basis of HSF1 regulation as well as available biochemical tools to investigate such details are lacking. Based on an in vitro ligand binding approach, the studies presented in this thesis were dedicated to the identification, validation, and characterization of a direct, first-in-class, small-molecule HSF1 inhibitor. The pharmacological inhibition of HSF1 occurs through small-molecule stimulation of nuclear, but not cytoplasmic HSF1 degradation, which attenuated prostate cancer cell proliferation, inhibited the HSF1 cancer gene signature and arrested tumor progression in multiple therapy-resistant animal models of prostate cancer. The identification of a direct small-molecule HSF1 inhibitor provides a unique pharmacological tool for future HSF1 research and serves as a significant proof-of-concept for pharmacologically targeting HSF1 for anti-cancer treatment approaches.

Heat Shock Transcription Factor 1 (HSF1) is a critical regulator of transcription that facilitates cellular stress protection in response to protein misfolding, rapid cell proliferation, and other stressful conditions. Defective HSF1 regulation is observed in cellular and animal models of cancer, where hyperactive and dysregulated HSF1 supports cancer survival, and in neurodegenerative disease, where HSF1 function is compromised, further exacerbating protein misfolding. HSF1 is tightly regulated through intramolecular interactions, post-translational modifications, and protein-protein interactions; however, little is known about ho HSF1 regulation differs in response to stresses such as acute or chronic protein misfolding.

We identified one mechanism that contributes to the diminution of HSF1 in chronic protein misfolding in the context of Huntington’s Disease involving inappropriate interactions of HSF1 with CK2α’ and FBXW7 E3 ligase. We found these protein-protein interactions coordinate the abnormal phosphorylation-dependent degradation of HSF1. Importantly, inhibition of this aberrant HSF1 degradation attenuates the biochemical defects and protein misfolding in Huntington’s Disease. To further elucidate how HSF1-interacting proteins regulate HSF1 in acute and chronic stress, we carried out quantitative proteomics studies of the HSF1 interactome under control, acute heat shock, and in a cell model of Huntington’s Disease. We recapitulated many previously described interaction partners of HSF1 and identified several novel HSF1-interacting proteins that encompass a wide variety of cellular functions, including roles in DNA repair, mRNA processing, and regulation of RNA polymerase II. We further report on the interaction of HSF1 with CCCTC binding factor (CTCF), which modulates target gene activation and repression function of HSF1 by facilitating DNA binding at CTCF and HSF1 co-regulated loci. Given the role and elevated expression of both pro-inflammatory proteins and Tau in Huntington’s Disease, and their defective repression by HSF1, understanding the mechanisms of HSF1 repression is of great interest. The studies presented in this thesis expand our understanding of HSF1-mediated gene activation and repression, and the regulation of HSF1 via protein-protein interactions.

Brain metastases are a devastating consequence of lung cancer resulting in significantly increased mortality. Currently, no effective therapies exist to treat brain metastases due to a lack of actionable targets and failure of systemic therapies to penetrate the blood-brain barrier (BBB). Using in vivo mouse models of brain metastasis combined with mechanistic cell signaling and transcriptomic approaches, the studies presented herein identify two actionable signaling pathways required during the colonization of metastatic lung cancer cells in the brain. First, we identify an autocrine AXL-ABL2-TAZ signaling axis in lung adenocarcinoma brain metastasis whereby nuclear accumulation of the TAZ transcriptional co-activator drives expression of ABL2 and AXL encoding protein tyrosine kinases which engage in bidirectional signaling. Activation of the ABL2 kinase in turn results in increased tyrosine phosphorylation of TAZ and enhances TAZ nuclear localization, thereby establishing an autocrine feed forward signaling loop. In addition to driving expression of ABL2 and AXL, TAZ also drives transcriptional activation of a number of neuronal-related gene targets, including L1CAM which was previously shown to promote metastatic colonization and outgrowth in the brain. Importantly, pharmacologic inhibition of the ABL kinases with BBB-penetrant ABL allosteric inhibitors disrupts AXL-ABL2-TAZ signaling and extends survival in brain metastasis-bearing mice. We also characterize an additional transcriptional program driven by Heat Shock Factor 1 (HSF1) and E2F family transcription factors during brain metastasis colonization that is required for survival of lung cancer cells at this organ site. Interestingly, the transcriptional program driven by HSF1 in the setting of brain metastasis is strikingly divergent from the canonical heat shock response, and loss of HSF1 markedly impairs colonization of tumor cells in in vivo models of brain metastasis. We identify ABL2 as a regulator of HSF1 and E2F protein expression and find that inhibition of ABL2 robustly impairs HSF1-E2F target gene expression. Collectively, our findings reveal ABL2 as a central hub of both AXL-ABL2-TAZ signaling and HSF1-E2F-coregulated transcription and provide evidence supporting the use of ABL kinase allosteric inhibitors for the treatment of lung cancer brain metastases.