Abstract 3594: P-glycoprotein attenuates Src activation and DNA repair activity via increased C-terminal Src kinase-binding protein, a negative regulator of Src, in multidrug-resistant cells

Abstract Multidrug resistance (MDR) remains a significant obstacle to the success of cancer chemotherapy. MDR is often associated with increased expression of ATP-binding cassette transporter family members, which extrude anticancer drugs out of cells. The MDR1 gene product, P-glycoprotein (P-gp) is one of the most well-known ABC transporters and expels a broad range of anticancer drugs, such as vinblastine, vincristine, doxorubicin and paclitaxel. Overexpression of P-gp in tumor tissues is thus a prognostic indicator associated with poor response to chemotherapy and poor clinical outcome. Our previous study has shown that P-gp overexpression attenuates the repair activity of DNA interstrand crosslinks (ICLs) and hence contributes the susceptibility of MDR cells to DNA ICL agents [1]. In the present study, we explored the molecular mechanisms underlying which P-gp interferes with Src-activated DNA repair activity. We first confirmed that ectopic expression of P-gp attenuates DNA ICL repair activity and becomes more susceptible to DNA ICL agents than vector control cells. Our present results showed that the C-terminal Src kinase-binding protein (Cbp), a negative regulator of Src, is significantly enhanced in MDR cells. Cbp silencing by siRNA technique apparently enhances cisplatin-induced Src activation and DNA repair activity, and hence increases the resistance of MDR cells to ICL agents. By aid of immuneprecipitation and immunofluorescence staining techniques, we demonstrated that P-gp not only interacts with Cbp and Src but also enhances the formation of inhibitory Csk-Cbp complex that reduces phosphorylation of Src activation residue Tyr416 and increases phosphorylation of Src negative regulatory Tyr527 residue. Taken together, the current results indicate that P-gp overexpression in MDR cells attenuates DNA repair activity by mediating Cbp dependent mechanism to interfere with Src activation. These results implicate that increasing the expression of Cbp is potentially a therapeutic strategy to increase the susceptibility of cancer cells to chemotherapeutic agents. 1. Lee PC, Lee HJ, Kakadiya R, Sanjiv K, Su TL, Lee TC: Multidrug-resistant cells overexpressing P-glycoprotein are susceptible to DNA crosslinking agents due to attenuated Src/nuclear EGFR cascade-activated DNA repair activity. Oncogene 2013, 32:1144-1154. Citation Format: Li-Fang Lin, Ming-Hsi Wu, Tsann-Long Su, Te-Chang Lee. P-glycoprotein attenuates Src activation and DNA repair activity via increased C-terminal Src kinase-binding protein, a negative regulator of Src, in multidrug-resistant cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3594. doi:10.1158/1538-7445.AM2015-3594