Browsing by Subject "ABL"

Adherens junctions are calcium-dependent cell-cell contacts formed during epithelial morphogenesis that link neighboring cells via cadherin receptors. Coordinated regulation of the actin cytoskeleton by the Rho GTPases is required for the formation and dissolution of adherens junctions, however the pathways that link cadherin signaling to cytoskeletal regulation remain poorly defined. The Abl family of tyrosine kinases have been shown to modulate cytoskeletal reorganization downstream of various extracellular signals including growth factor receptors and integrins.

Here we use pharmacological inhibition and RNA interference to identify the Abl family kinases as critical mediators of cadherin-mediated adhesion. Endogenous Abl family kinases, Abl and Arg, are activated and are required for Rac activation following cadherin engagement, and regulate the formation and maintenance of adherens junctions in mammalian cells. Significantly, we show that Abl-dependent regulation of the Rho-ROCK-myosin signaling pathway is critical for the maintenance of adherens junctions. Inhibition of the Abl kinases in epithelial sheets results in activation of Rho and its downstream target ROCK, leading to enhanced phosphorylation of the myosin regulatory light chain. These signaling events result in enhanced stress fiber formation and increased acto-myosin contractility, thereby disrupting adherens junctions. Conversely, Arg gain-of-function promotes adherens junction formation through a Crk-dependent pathway in cells with weak junctions. These data identify the Abl kinases as a novel regulatory link between the cadherin/catenin adhesion complex and the actin cytoskeleton through regulation of Rac and Rho during adherens junction formation.

Unexpectedly, we identified a requirement for Abl and Crk downstream of Rac in the regulation of adherens junctions. Therefore, Abl functions both upstream and downstream of Rac in regulating adherens junctions, which suggests the possibility of a positive feedback loop consisting of Abl-Crk-Rac.

Finally, we identified the Abl kinases as critical mediators of epithelial cell response to HGF. Pharmacological inhibition of Abl kinase activity resulted in impaired dissolution of adherens junctions downstream of HGF stimulation of the Met receptor. Additionally, we observed decreased phosphorylation of the Met receptor itself, along with Gab1 and Crk, downstream effectors of Met signaling. Taken together, these data suggest a requirement for Abl kinases in both adherens junctions formation and turnover.

Metastases are common and devastating complications linked to ~90% of cancer deaths. Therapy-resistance is a major challenge for the treatment of cancer cell metastasis as metastatic cells metabolically rewire to survive cytotoxic therapies and adapt to new environments. Understanding and effectively targeting these metabolic changes opens an entirely new therapeutic avenue for combating cancer by defining cancer-related metabolic vulnerabilities. Using a CRISPR/Cas9 loss-of-function screen and RNA-sequencing analysis, the studies presented herein identify two metabolic vulnerabilities that arise following ABL allosteric inhibitor treatment to target metastatic and therapy-resistant cancer cells. First, we identify a novel combination therapy of ABL kinase allosteric inhibitors with lipophilic statins that impairs growth of clinically relevant therapy-resistant and brain metastatic lung cancer cells in vitro and in in vivo using mouse models. We found that ABL allosteric inhibitors impair mitochondria function without altering glycolytic capacity, leading to sensitization to statin therapeutics, and enhanced synergy to promote cancer cell death by combination therapy. Further, we found that ABL inhibitors are sensitized to statins due to the ability of statin therapeutics to inhibit the isoprenoid pathway, specifically protein geranylgeranylation. These results reveal a potential striking clinical benefit as synergy was not noted upon combination with standard of care therapeutics, gefitinib and docetaxel, and identify a new treatment strategy for patients refractory to first-line therapeutics or with metastases to difficult to treat organs like the brain. We have also characterized a novel ABL signaling axis as ABL inhibition was shown to deplete SLC7A11 protein levels in cancer cells. SLC7A11 is the catalytic subunit of system xCT and enables cystine import for cell detoxification and concomitant glutamate export. By depleting cancer cells of SLC7A11, cell detoxification processes are limited and excretion of toxic glutamate levels into the tumor microenvironment decrease. These data suggest that ABL regulation of this pathway could extend survival and relieve harmful symptoms in patients experiencing primary and secondary metastatic tumors. Collectively, our findings reveal metabolic vulnerabilities that can be targeted in cancer cells through treatment with ABL allosteric inhibitors, leading to improved patient survival and quality of life.

The ABL family of non-receptor tyrosine kinases, ABL1 (also known as c-ABL) and ABL2 (also known as Arg), links diverse extracellular stimuli to signaling pathways that control cell growth, survival, adhesion, migration and invasion. ABL tyrosine kinases play an oncogenic role in human leukemias. However, the role of ABL kinases in solid tumors including breast cancer progression and metastasis is just emerging.

To evaluate whether ABL family kinases are involved in breast cancer development and metastasis, we first analyzed genomic data from large-scale screen of breast cancer patients. We found that ABL kinases are up-regulated in invasive breast cancer patients and high expression of ABL kinases correlates with poor prognosis and early metastasis. Using xenograft mouse models combined with genetic and pharmacological approaches, we demonstrated that ABL kinases are required for regulating breast cancer progression and metastasis to the bone. Using next generation sequencing and bioinformatics analysis, we uncovered a critical role for ABL kinases in promoting multiple oncogenic pathways including TAZ and STAT5 signaling networks and the epithelial to mesenchymal transition (EMT). These findings revealed a role for ABL kinases in regulating breast cancer tumorigenesis and bone metastasis and provide a rationale for targeting breast tumors with ABL-specific inhibitors.