Adhesion of renal carcinoma cells to endothelial cells depends on PKCμ

Background: The formation of metastases includes the separation of tumor cells from the primary tumor, cell migration into subendothelial tissue and cell proliferation in secondary organ. In this process, cell adhesion of tumor cells to the endothelium is an essential requirement for formation of metastases. Protein kinase C (PKC) regulates adhesion and proliferation. To identify a relation between PKC isoforms and tumor progression in renal cell carcinoma (RCC), the influence of PKC isoforms on cell adhesion and proliferation, and possible influences of integrins were analyzed in RCC cells. Methods: The experiments were performed in the RCC cell lines CCF-RC1 and CCF-RC2 after pre-incubation (16 h) with the PKC inhibitors GF109203X (inhibits PKC alpha, beta I, beta II, gamma, delta and epsilon), G 6976 (inhibits PKC alpha, beta I and mu), RO31-8220 (inhibits PKC alpha, beta I, beta II, gamma and epsilon) and rottlerin (inhibits PKC delta). Cell adhesion was assessed through adherence of RCC cells to an endothelial monolayer. Cell proliferation was analyzed by a BrdU incorporation assay. The expression of beta 1 integrins was analyzed by flow cytometry. Results: In CCF-RC1 cells, cell adhesion was significantly reduced by GO6976 to 55% and by RO31-8220 to 45% of control. In CCF-RC2 cells, only GO6976 induced a significant reduction of cell adhesion to 50% of control levels. Proliferation of both cell lines was reduced by rottlerin to 39% and 45% of control, respectively. The beta 1 integrin expression on the cell surface of CCF-RC1 and CCR-RC2 cells was decreased by RO31-8220 to 8% and 7% of control, respectively. beta 2 and beta 3 integrins were undetectable in both cell lines. Conclusions: The combination of the PKC inhibitors leads to the assumption that PKC mu influences cell adhesion in CCF-RC1 and CCF-RC2 cells, whereas in CCF-RC1 cells PKC epsilon also seems to be involved in this process. The expression of beta 1 integrins appears to be regulated in particular by PKC epsilon. Cell proliferation was inhibited by rottlerin, so that PKC delta might be involved in cell proliferation in these cells.