Cell Cycle and Senescence A Novel Regulatory Mechanism of Pim-3 Kinase Stability and Its Involvement in Pancreatic Cancer Progression

Translationally controlled tumor protein (TCTP/TPT1) was identified from a yeast 2-hybrid screen and shown to interact with Pim-3, a member of the proto-oncogene Pim family with serine/threonine kinase activity. TCTP was aberrantly expressed in human pancreatic cancer cells and malignant ductal epithelial cells, but not in normal pancreatic duct epithelial cells adjacent to tumor foci of human pancreatic cancer tissue. Moreover, TCTP colocalized with Pim-3 both in human pancreatic cancer cells and in clinical tissues. Mapping studies revealed that the interaction between Pim-3 and TCTP occurred through the C-terminal region of Pim-3 andN-terminal region of TCTP. Although Pim-3 had no effect on TCTP expression or phosphorylation, overexpression of TCTP increased the amount of Pim-3 in a dose-dependent manner. Interestingly, RNAi-mediated ablation of TCTP expression reduced Pim-3 protein but not mRNA, through a mechanism involving the ubiquitin–proteasome degradation system. As a consequence of Pim-3 instability and subsequent degradation, tumor growth in vitro and in vivo was inhibited by arresting cell-cycle progression and enhancing apoptosis. Furthermore, TCTP and Pim-3 expression were significantly correlated in pancreatic adenocarcinoma specimens, and patients with highly expressed TCTP and Pim-3 presented with a more advanced tumor stage. These observations indicate that TCTP enhances Pim-3 stability to simultaneously promote and prevent cell-cycle progression and apoptosis, respectively. Hence, TCTP and Pim-3 serve a pivotal role in human pancreatic cancer with important ramifications for clinical diagnostic and therapeutic implications. Implications: The present study provides a new idea and experimental evidence for recognizing TCTP/Pim-3 pathway as a target for therapy in human pancreatic cancer. Mol Cancer Res; 11(12); 1508–20. 2013 AACR. Introduction Pim-3, a member of the proto-oncogene Pim family with serine/threonine kinase activity, was originally identified as a depolarization-induced gene, KID-1, in the rat pheochromocytoma cell line PC12 (1). Later, KID-1 was renamed Pim-3 because of its high sequence similarity with Pim family proteins, which belong to the group of calcium/calmodulin-regulated kinase (1). Subsequently, Deneen and colleagues demonstrated that Pim-3 gene transcription was enhanced in EWS/ETS-induced malignant transformation of NIH3T3 cells (2), suggesting the involvement of Pim-3 in tumorigenesis. In line with these observations, we demonstrated that Pim-3 expression was enhanced in malignant lesions, but not normal tissues of endoderm-derived organs such as the liver (3), pancreas (4), colon (5), and stomach (6). Hepatocellular carcinoma development was accelerated in mice expressing the Pim-3 transgene selectively in liver, when these mice were treated with a hepatocarcinogen (7). We observed that Pim-3 can inactivate Bad in human pancreas and colon carcinoma cell lines by phosphorylating Ser, but not Ser, and ultimately promoting their survival (4, 5) as observed for Pim-1 and Pim-2 (8, 9). Moreover, it has been reported that Pim-3 can promote cell-cycle progression by modulating the functions of molecules that regulate cell-cycle progression and augment protein synthesis through the regulation of PGC-1a, eventually contributing to carcinogenesis (10). Baines and colleagues recently reported that Pim-3 suppression can sensitize pancreatic cancer cells to gemcitabine (11). We also demonstrated that Pim-3 can promote tumor growth and angiogenesis by stimulating the VEGF pathway (12). Furthermore, Pim-3 modulates Myc activity to promote tumorigenesis (13). Authors' Affiliations: Cancer Research Institute; Department of Pancreas and Hepatobiliary, Pancreatic Cancer Institute; Department of Pathology, Fudan University Shanghai Cancer Center; Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China; and Division of Molecular Bioregulation, Cancer Microenvironment Research Program, Cancer Research Institute, Kanazawa University, Kanazawa, Japan Note: Supplementary data for this article are available at Molecular Cancer Research Online (http://mcr.aacrjournals.org/). Corresponding Author: Professor Ying-Yi Li, Room 1216, 2nd Building, Cancer Research Institute, Fudan University Shanghai Cancer Center, 270 DongAn Road, Shanghai 200032, China. Phone: 86-21-64175590-5220; Fax: 86-21-64172585; E-mail: [email protected] doi: 10.1158/1541-7786.MCR-13-0389 2013 American Association for Cancer Research. Molecular Cancer Research Mol Cancer Res; 11(12) December 2013 1508 on June 19, 2017. © 2013 American Association for Cancer Research. mcr.aacrjournals.org Downloaded from Published OnlineFirst October 28, 2013; DOI: 10.1158/1541-7786.MCR-13-0389