A kinase-directed RNAi screen identifies GSK-3b/a as a target to overcome drug resistance of p53-null colon cancer cells

Abstract

Abstract Evasion from chemotherapy-induced apoptosis strongly contributes to drug resistance and tumor relapse. In particular, p53 loss renders colon carcinoma cells resistant to 5-fluorouracil-induced apoptosis. We have used the 5-fluorouracil-resistant HCT116p53KO colon carcinoma cell line and a kinase-directed retroviral shRNA library to identify kinases whose inactivation reverts resistance to drug-induced apoptosis. In this way we have identified 29 kinases whose downregulation abolished colony growth after 5-fluorouracil treatment. Silencing of these kinases in other drug-resistant p53-null colon cell lines also abolished cellular growth, suggesting that the effect is independent of the genetic background. We focused on GSK-3 since by tissue microarray we found that GSK-3 is overexpressed/activated in tumoral biopsies of infiltrating and invasive colon carcinomas. We demonstrated that GSK-3 silencing in different colon carcinoma cell lines reverts resistance not only to 5-fluorouracil, but also to oxaliplatin and the 2 drugs used in combination. Interestingly, we found that 5-fluorouracil-treated p53-null GSK-3-depleted colon carcinoma cells undergo caspase-independent but PARP-dependent and tBid- and AIF-mediated cell death. Therefore, we propose that GSK-3 is an excellent potential target for the development of anti-cancer therapy. Our results suggest that inhibitors of GSK-3 can be used in combination with chemotherapy to kill cancer cells unable to trigger caspase-dependent apoptosis.