Phosphorylation of TOPK at Y74, Y272 by Src increases the stability of TOPK and promotes tumorigenesis of colon

// Juanjuan Xiao 1, 4, * , Qiuhong Duan 1, * , Zhe Wang 3 , Wei Yan 3 , Huimin Sun 2 , Peipei Xue 1 , Xiaoming Fan 1 , Xiaoyu Zeng 1 , Juan Chen 1 , Chen Shao 2 , Feng Zhu 1 1 Department of Biochemistry and Molecular Biology, School of Basic Medicine, Huazhong University of Science and Technology, Wuhan, Hubei, 430030, PR China 2 Department of Urology, Xijing Hospital, the Fourth Military Medical University, Xi’an, Shaanxi, 710032, PR China 3 Department of Pathology, Xijing Hospital, the Fourth Military Medical University, Xi’an, Shaanxi, 710032, PR China 4 Laboratory for Translational Oncology Basic Medicine College, Hubei University of Science and Technology, Xianning, Hubei, 437100, PR China * Juanjuan Xiao and Qiuhong Duan contributed equally to this article and should be considered as co-first authors Correspondence to: Juan Chen, e-mail: chenjuanlinda69@163.com Chen Shao, e-mail: shaochen@fmmu.edu.cn Feng Zhu, e-mail: fengzhu@hust.edu.cn Keywords: TOPK, Src, colon cancer, tumorigenesis, stability Received: January 06, 2016     Accepted: March 04, 2016     Published: March 21, 2016 ABSTRACT T-LAK cell-originated protein kinase (TOPK), a serine/threonine protein kinase, is highly expressed in a variety of tumors and associated with a poor prognosis of human malignancies. However, the activation mechanism of TOPK is still unrevealed. Herein, first we found that Src directly bound with and phosphorylated TOPK at Y74 and Y272 in vitro . Anti-phospho-TOPK at Y74 was prepared, the endogenous phosphorylation of TOPK at Y74 was detected in colon cancer cells, and the phosphorylation was inhibited in cells expressing low levels of Src. Subsequently, we stably transfected Y74 and Y272 double mutated TOPK (TOPK-FF) into JB6 or SW480 cells, and observed that both the anchorage-independent growth ability and tumorigenesis of TOPK-FF cells were suppressed compared with those of wild type TOPK (TOPK-WT) ex vivo and in vivo. The phosphorylation level of TOPK substrate, Histone H3 at Ser10 also decreased dramatically ex vivo or in vivo . Moreover, we showed that Src could inhibit the ubiquitination of TOPK. Transiently expressed TOPK-WT was more stable than TOPK-FF in pause and chase experiment. Endogenous TOPK was more stable in Src wild type (Src +/+ ) MEFs than in Src knockout (Src -/- ). Taken together, our results indicate that Src is a novel upstream kinase of TOPK. The phosphorylation of TOPK at Y74 and Y272 by Src increases the stability and activity of TOPK, and promotes the tumorigenesis of colon cancer. It may provide opportunities for TOPK based prognosis and targeted therapy for colon cancer patients.