Circadian Clock Gene CRY2 Degradation Is Involved in Chemoresistance of Colorectal Cancer.

Biomarkers for predicting chemotherapy response are important to the treatment of colorectal cancer patients. Cryptochrome 2 (CRY2) is a circadian clock protein involved in cell cycle, but the biologic consequences of this activity in cancer are poorly understood. We set up biochemical and cell biology analyses to analyze CRY2 expression and chemoresistance. Here, we report that CRY2 is overexpressed in chemoresistant colorectal cancer samples, and CRY2 overexpression is correlated with poor patient survival. Knockdown of CRY2 increased colorectal cancer sensitivity to oxaliplatin in colorectal cancer cells. We also identify FBXW7 as a novel E3 ubiquitin ligase for targeting CRY2 through proteasomal degradation. Mechanistic studies show that CRY2 is regulated by FBXW7, in which FBXW7 binds directly to phosphorylated Thr300 of CRY2. Furthermore, FBXW7 expression leads to degradation of CRY2 through enhancing CRY2 ubiquitination and accelerating the CRY2's turnover rate. High FBXW7 expression downregulates CRY2 and increases colorectal cancer cells' sensitivity to chemotherapy. Low FBXW7 expression is correlated with high CRY2 expression in colorectal cancer patient samples. Also, low FBXW7 expression is correlated with poor patient survival. Taken together, our findings indicate that the upregulation of CRY2 caused by downregulation of FBXW7 may be a novel prognostic biomarker and may represent a new therapeutic target in colorectal cancer. ©2015 American Association for Cancer Research.