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

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.

Emerging actionable targets to treat therapy-resistant colorectal cancers

“…Many promising synthetic lethal vulnerabilities, whose targeting kills p53-null drug resistant-resistant CRC cells, have been identified by an shRNA screen performed in our lab [ 41 ] . Several of them have successively been validated by other labs such as PIM-1 [ 42 ] , TRIB3 [ 43 ] , EPHA2 [ 44 , 45 ] , CHK1 [ 46 ] , and VEGFR2 [ 47 ] .…”