The role of the HSP90 cochaperone CDC37 and its therapeutic potential in cancer

The cochaperone CDC37 promotes recruitment of a subset of client proteins, predominantly protein kinases, to the HSP90 chaperone, thereby regulating the activity of several signalling pathways including those altered in malignancy. Here, an investigation of CDC37's role in chaperoning clients in cancer cells was undertaken to test the hypothesis that targeting CDC37 may be therapeutically beneficial in cancer. To study the function of CDC37, expression or activity was modulated. Overexpression of CDC37 did not affect the steady state levels or activity of kinase clients such as CRAF and AKT; however, CDK4 expression was consistently elevated compared with controls.CDK4 protein half-life and CDK4-HSP90 association were also increased, suggesting that CDC37 is rate-limiting for CDK4 stability. Following overexpression of CDC37, CDK4 was depleted to a lesser extent following 17-AAG treatment; however, the sensitivity to HSP90 inhibitors, assessed by GI50, was unchanged. Conversely, siRNA-mediated CDC37 silencing caused depletion of clients such as ERBB2, CRAF, CDK4 and CDK6 by a proteasome-dependent mechanism and inhibited both activation of downstream signalling pathways and cell proliferation. Furthermore, CDC37 silencing sensitised cells to HSP90 inhibitors by potentiating kinase client depletion, cell cycle arrest and apoptosis. Expression of a CDC37 mutant deficient in binding to HSP90 caused an accumulation of endogenous CDC37 and client proteins in high molecular weight complexes corresponding to HSP90. Increased CDK4-HSP90 association without any effect on CDK4 expression was also observed, suggesting that CDC37 is required in the chaperone complex to correctly load client proteins. Additionally, it was found that the phosphatase PP5 can dephosphorylate CDC37 and influence the maturation of kinase client proteins, suggesting that it may regulate CDC37 activity in the chaperone cycle. In conclusion, by modulation of CDC37, its critical role in concert with HSP90 to stabilise kinase clients has been demonstrated, supporting the therapeutic potential of targeting CDC37 in cancer.EThOS - Electronic Theses Online ServiceGBUnited Kingdo