A study of the interaction between RHOC GTPase and AKT in prostate cancer cells adhering to collagen Type I

Drummer, Charles
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University of Delaware
Hormone refractory metastatic prostate cancer (PCa) cannot be cured. The aim of treatment at this stage is to prolong life, improve symptoms, and slow disease progression. Docetaxel is the standard therapy for hormone refractory metastatic PCa. Docetaxel alone or in combination with other agents improves survival, however inevitably PCa becomes chemoresistant. Initial discoveries regarding chemoresistance were performed under in vitro conditions, and accordingly fail to take into account environmental factors such as cell-cell or cell-extracellular matrix (ECM) interactions. Unpublished preliminary data from the Cooper laboratory demonstrated that Akt is activated in PCa cell adhering to the ECM component collagen type I. When adhered to collagen type I, the viability of PCa cells is increased in the presence of docetaxel compared to control and fibronectin. In addition to Akt, the Rho family of GTPases is also frequently upregulated in human cancers. Results published by Ruth and Xu suggest that RhoC promotes invasion in part through the PI3K/Akt pathway. We hypothesize that the in vitro adhesion of PC-3 cells to collagen type I mediates the activation of Akt via RhoC. To accomplish this we sought to demonstrate that 1) adhesion of PC-3 cells to collagen type I upregulates Akt in PC-3 cells, 2) the use of a RhoC inhibitor, C3 transferase, will decrease the Akt activation in PC-3 cells adhering to collagen type I, and 3) to determine if Akt activation is required to stimulate RhoC GTPase in PC-3 cells adhering to collagen type I. We confirmed our first aim by demonstrating that Akt expression was about 3 times greater in the collagen type I sample than was Akt expression in the fibronectin or uncoated plates samples. We also saw greater P-Akt expression in response to collagen type I as opposed to growth on fibronectin. Contrary to our hypothesis, the experiments for specific aim 2 demonstrated that RhoC has an inhibitory effect on ECM stimulated Akt expression and activation. Total Akt levels in C3- collagen type I sample were 75% of the Akt expression in C3+ collagen sample. The C3- fibronectin sample was less than half that of its C3+ counterpart. P-Akt expression for both C3- collagen type I and fibronectin samples were 76% that of the expression for the C3+ samples. Future directions for this work include redesigning specific aim 3 and repeating all experiments to enable statistical analysis.