Cleavage of ROCK II: As a Common Phenomenon in Cell Death

We have previously showed that caspase‐2 cleaved Rho kinase II (Rock II), one of the Rho kinase isoforms and produced a novel ~140 kDa fragment of the enzyme in HUVEC during ouabain‐induced apoptosis. In the current work we evaluated whether this cleavage is a common process in cell death. To test this hypothesis two different types of cancer cell lines HeLa and HepG2 were exposed to two different cardiac glycosides (1μM, 18h); ouabain, digoxin and a standard chemotherapeutic; paclitaxel (1 μM, 18 h) to induce cell death. After the induction, the effect of Rock inhibitor Y‐27632 (10 μM, 30 min before ouabain) and caspase inhibitors (50 μM, 2h before ouabain); caspase‐2 inhibitor z‐VDVAD‐fmk, caspase‐3 inhibitor Z‐DEVD‐fmk and pan caspase inhibitor z‐VAD‐fmk on cell death were examined. Treatment of ouabain, digoxin and paclitaxel resulted in concentration dependent cell‐substratum detachment and cell death. Neither Y‐27632 nor caspase inhibitors did not prevent drug‐induced cell detachment. Ouabain, digoxin and also paclitaxel treatment induced cleavage of Rock II in both HeLa and HepG2 cells. Although this cleavage was not inhibited by Y‐27632, all the caspase inhibitors prevented the proteolytic clevage of Rock II. It has been demonstrated that activation of caspase‐3 results in cleavage and activation of caspase‐2. Therefore our results point out that drug treatment induces activation of caspase‐3, which produces active caspase‐2 causing proteolytic cleavage of Rock II in cancer cells during cell death. As a conclusion, cleavage of Rock II by caspase‐2 is a common process in a cell‐type independent manner in cell death. This study is supported by TUBITAK in 110S426 project.