Differential regulation of cellular functions by the C-termini of transmembrane 4 L six family proteins in 2- or 3-dimensional environment

// Jin-Gyu Cheong 1 , Dae-Geun Song 1, 2 , Haeng Eun Song 1 , Fedor Berditchevski 3 , Seo Hee Nam 4 , Jae Woo Jung 4 , Hye-Jin Kim 1 , Ji Eon Kim 1 , Somi Kim 1 , Jihye Ryu 1 , Chang Yun Cho 1 , Kyung-Min Lee 1 , Jung Weon Lee 1, 4 1 Department of Pharmacy, Research Institute of Pharmaceutical Sciences, College of Pharmacy, Seoul National University, Seoul 08826, Republic of Korea 2 Systems Biotechnology Research Center, Korea Institute of Science and Technology (KIST), Gangneung-si, Gangwon-do 25451, Republic of Korea 3 Institute of Cancer and Genomic Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK 4 Interdisciplinary Program in Genetic Engineering, Seoul National University, Seoul 08826, Republic of Korea Correspondence to: Jung Weon Lee, email: jwl@snu.ac.kr Keywords: 3D cell culture, migration, proliferation, spheroids, transmembrane 4 L six family Received: August 20, 2016      Accepted: December 27, 2016      Published: January 25, 2017 ABSTRACT The transmembrane 4 L six family proteins TM4SF1, TM4SF4, and TM4SF5 share 40-50% overall sequence identity, but their C-terminus identity is limited. It may be likely that the C-termini of the members are important and unique for own regulatory functions. We thus examined how the TM4SF5 C-terminus affected cellular functions differentially from other family members. Using colon cancer cells expressing wildtype (WT), C-terminus-deleted, or chimeric mutants, diverse cellular functions were explored in 2-dimensional (2D) and 3-dimensional (3D) condition. The C-termini of the proteins were relatively comparable with respect to 2D cell proliferation, although each C-terminal-deletion mutant exhibited increased proliferation relative to the WT. Using chimeric constructs, we found that the TM4SF5 C-terminus was critical for regulating the diverse metastatic functions of TM4SF5, and could positively replace the C-termini of other family members. Replacement of the TM4SF1 or TM4SF4 C-terminus with that of TM4SF5 increased spheroids growth, transwell migration, and invasive dissemination from spheroids in 3D collagen gels. TM4SF5-mediated effects required its extracellular loop 2 linked to the C-terminus via the transmembrane domain 4, with causing c-Src activation. Altogether, the C-terminus of TM4SF5 appears to mediate pro-migratory roles, depending on a structural relay from the second extracellular loop to the C-terminus.