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.
대장암 전이 조절 후보 인자로서 신규유전자 TMEM52B을 선정하였다. TMEM52B는 세포막도메인을 가지고 있고, N-말단서열이 다른 2개의 아형 (163 아미노산 및 183아미노산)이 보고되었다. TMEM52B 발현억제에 의해 대장암 세포 침윤능과 생존이 증가하고, EGFR의 티로신 1068이 인산화 되며EGFR의 하위 신호분자인 JNK, ERK1/2와 AKT 신호들이 활성화 되었다. 이 과정 중p38에 의해 EGFR의 세린1046/47을 인산화되고 EGFR 내재화가 유도되었다. TMEM52B가 E-cadherin과 결합하여 단백질 안정화하였고, TMEM52B발현억제에 의해 β-catenin이 활성화되고 핵으로 이동되었다. 또한 TMEM52B의 세포외도메인 서열에서 유래한 펩타이드에 의해 EGFR의 인산화가 감소하고 ERK1/2와 AKT 신호전달이 감소하여 세포 침윤능과 생존이 억제되었다. 또한, 펩타이드-Fc 융합단백질에 의해 EGFR의 내재화가 유도되었다. 결론적으로, TMEM52B이 종양억제 활성을 가지며, EGFR 내재화를 조절한다. 이러한 결과들은 대장암 전이기작을 이해하고 TMEM52B를 기반으로 한 새로운 암 바이오마커 발굴 및 치료물질개발에 기여할 수 있다.
