Functional analysis of TMEM52B and its application for colorectal cancer therapy

Abstract

Colorectal cancer (CRC) is one of the highly metastatic malignant tumors with high mortality worldwide. However, the molecular mechanism underlying CRC metastasis has not been clearly elucidated. In an effort to determine the resulting factors of CRC metastasis, several genetic and proteomic experiments were conducted in highly invasive subpopulation of SW480 cells, and transmembrane protein 52B (TMEM52B) was selected as a novel candidate regulator of CRC metastasis. TMEM52B is a novel gene, which has a transmembrane domain and two isoforms with a distinct N-terminus (163a.a and 183a.a) have been identified. In this study, I investigated the function of TMEM52B in CRC metastasis by genetic manipulation methods such as gene knockdown technologies and ectopic TMEM52B overexpression in CRC cells. Inhibition of TMEM52B increased cancer cell invasion and survival by phosphorylating Y1068 on EGFR to activate the downstream signaling including JNK, ERK1/2, and JNK pathways. Internalization of EGFR was induced by p38-mediated phosphorylation at S1046/47 following TMEM52B suppression. In addition, when TMEM52B was suppressed, E-cadherin stability was reduced and β-catenin was phosphorylated/activated and translocated into nucleus to possibly stimulate the transcription of EMT related genes. TMEM52B interacted with EGFR and reduced basal and EGF-induced invasion of HEK293E cells co-expressing TMEM52B and EGFR. The potential of TMEM52B in therapeutic application was tested using peptides encoding the extracellular domains of TMEM52B isoforms. Treatment of the peptides reduced phosphorylation of EGFR, AKT and ERK1/2, leading to suppression of cancer cell invasion and survival. Peptide fused with Fc induced the EGFR internalization and reduced liver and lung metastasis in vivo. Clinical analysis of cancer database revealed that high TMEM52B expression in breast and lung adenocarcinoma patients was significantly correlated with increased relapse-free survival or overall survival, respectively. These findings will help understand the molecular mechanisms of CRC metastasis and development of a novel biomarker and/or therapeutics.