HSP70 and HSP90 Inhibitors Repress Expression of TSC1 in T24 Bladder Cancer Cells and UOK139, UOK 140 Kidney Cancer Cells

Abstract

Normal cells are able to survive in stressful conditions by increased expression of heat shock protein (HSP) genes. Both HSP90 and HSP70 are up regulated in cancers of the bladder and kidney. Next generation sequencing studies have identified pathways involved in kidney and bladder cancer. The objective of this study was to elucidate the impact of HSP70 and HSP90 inhibition on the signal transduction pathways driving their tumorigenic process. The TSC1‐TSC2 complex has emerged as a central signal‐integrating node within the cell.MethodsWe analyzed the expression of key mediators of the TSC1‐TSC2 pathway when treated with the HSP90 inhibitor (STA9090) or HSP70 inhibitors (VER155008, MAL3‐101) in bladder cancer (T24) and kidney cancer (UOK139 and UOK140) cell lines. The impact of treatment on cell growth was analyzed using a MTT assay and on signal protein expression by Western blot analyses.ResultsGrowth inhibition was seen in T24 bladder cancer cells when treated with 1 μM STA9090 (STA) and 50 μM VER155008 (VER) but not with 30 μM MAL3‐101 (MAL) for 72 h. Synergistic growth inhibition was seen with combination STA+VER, STA+MAL and MAL+VER in T24 cell lines. We tested the effect of these inhibitors on the expression of TSC pathway mediators in both bladder and kidney cancer cell lysates and noted that TSC1 was down regulated in all cell lines tested in the presence STA and VER. In T24 cells, only the combination VER + MAL led to TSC1 down regulation. Neither STA, VER nor MAL had any impact on S6 kinase (a downstream mediator) expression in T24 cells. Rather, only STA and not VER or MAL downregulated the expression of the active form of S6 kinase (pS6kinase).ConclusionThe inhibition of HSP70 and HSP90 appears to cause a down regulation of TSC1. TSC1/2 functions as a GTPase‐activating protein (GAP) for the small Ras‐related GTPase Rheb. The active, GTP‐bound form of Rheb directly interacts with mTORC1 to stimulate its activity. mTORC1 promotes protein synthesis by phosphorylating S6 kinase. Together, these data suggest a role for HSP90 and HSP70 inhibitors in kidney and bladder cancer management.Support or Funding InformationBucknell‐Geisinger Research Initiative