Cloning of cDNA Encoding Putative Cellular Receptor Interacting with E2 protein of Hepatitis C Virus

C형 간염바이러스 E2 단백질에 결합하는 추정 세포수용체 cDNA의 클로닝

E2 glycoprotein of hepatitis C virus (HCV) comprises a surface of viral particle together with E1 glycoprotein, and is thought to be involved in the attachment of HCV viral particle to receptor (s) on the permissible cells including hepatocytes, B cells, T cells, and monocytes. We constructed a phage library expressing cellular proteins of hepatocytes on the phage surface, which turned out to be 8.8${\times}$$10^5$ cfu of diversity and carried inserts in 95% of library. We screened both cDNA phage library and 12-mer peptide library to identify the cellular proteins binding to E2 protein. Some intracellular proteins including tensin and membrane band 4.1 which are involved in signal transduction of survival and cytoskeleton organization, were selected from cDNA phage library through several rounds of panning and screening. On the contrary, membrane proteins such as CCR7, CKR-L2, and insulin-like growth factor-1 receptor were identified through screening of peptide library. Phages expressing peptides corresponding to those membrane proteins were bound to E2 protein specifically as determined by neutralization of binding assay. Since it is well known that HCV can infect T cells as well as hepatocytes, we examined to see if E2 protein can bind to CCR7, a member of C-protein coupled receptor family expressed on T cells, using CCR7 transfected tells. Human CCR7 cDNA was cloned into pcDNA3.1(-) vector and transfected into human embryonic kidney cell, 293T, and expressed on the surface of the cell as shown by flow cytometer. Binding assay of E2 protein using CCR7 transfected cells indicated that E2 protein bound to CCR7 by dose-dependent mode, giving rise to the possibility that CCR7 might be a putative cellular receptor for HCV.

본 실험에서는 C형 간염바이러스 (HCV)의 외피 단백질인 E2 당단백질에 결합하는 세포단백질들을 클로닝하기 위해 간세포 cDNA를 phage 표면에 발현시킨 phage library를 제작하였고, 12-mer peptide library와 함께 E2 단백질에 대해 panning을 실시하였다. 검색결과 세포내 신호전달과 cytoskeleton 구성에 관여하는 tensin, membrane protein band 4.1 등 세포질내 단백질과 CCR7, CKR-L2, insulin-like growth factor-1 receptor 등 세포막 단백질 등이 확인되었다. 이들 단백질들을 발현하는 phage들은 수용성 E2단백질을 이용한 결합중화반응 결과 E2 단백질에 특이적으로 결합함이 확인되었다. 사람 T 세포에서 주로 발현되는 CCR7 유전자를 PHA로 활성화된 사람 T 세포의 total RNA를 이용하여 증폭하고 클로닝하였다. 293T 세포에 transfection시켜 단백질 발현양상을 flow cytometer로 분석하여 70% 이상의 세포들이 CCR7을 발현하고 있음을 관찰하였다. 수용성 E2 단백질을 CCR7이 transfection된 세포와 mock transfection된 대조군 세포에 각각 반응시킨 결과 dose-dependent 양상으로 CCR7에 결합하였다.