Phosphorylation of USP32 by CDK5 regulates Rap1 stability and therapeutic resistance in pancreatic ductal adenocarcinoma.

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal human cancer. Gemcitabine-based chemotherapy remains the cornerstone for advanced PDAC. However, resistance to chemotherapy greatly limits its clinical therapeutic efficacy. Accordingly, the identification of novel therapeutic targets to overcome chemoresistance and improve prognosis is urgently needed. Screening of deubiquitinase family members, tandem affinity purification, mass spectrometry, and RNA sequencing (RNA-Seq) analysis were performed to predict the interactions and function of the CDK5-USP32-Rap1 axis in PDAC. In vitro and in vivo experiments were performed to elucidate the regulatory mechanism and biological roles of this axis in glycolytic reprogramming and chemoresistance in PDAC. Finally, TCGA database analysis and immunohistochemistry were performed to determine the expression and clinical significance of CDK5, USP32, and Rap1 in PDAC tissues. USP32 was identified as a bona fide deubiquitinase of Rap1. USP32 deubiquitinates and stabilizes Rap1, thereby promoting glycolytic reprogramming and chemoresistance in PDAC cells. Moreover, we unexpectedly found that CDK5-mediated phosphorylation of USP32 is required for its deubiquitinase activity toward Rap1 and drives malignant phenotypes of PDAC. Additionally, these functions can be significantly inhibited by pharmacological inhibition (roscovitine) or genetic ablation of CDK5. Importantly, combining a CDK5 inhibitor with gemcitabine has a synergetic anticancer effect. Indeed, the effectiveness of targeting CDK5 to sensitize PDAC cells to gemcitabine was confirmed in a patient-derived xenograft (PDX) model. CDK5 and USP32 expression is markedly elevated in PDAC samples and positively associated with Rap1 expression. Increased expression of CDK5, USP32, and Rap1 is significantly associated with poorer prognosis in PDAC. We identified the previously unrecognized oncogenic function and clinical importance of the CDK5-USP32-Rap1 axis, providing preclinical evidence for potential new combination strategies for PDAC therapy.