Identification of factors interacting with hMSH2 in the fetal liver utilizing the yeast two-hybrid system - In vivo interaction through the C-terminal domains of hEXO1 and hMSH2 and comparative expression analysis

Mutations in DNA mismatch repair (MMR) genes have been shown to segregate w ith Hereditary Nonpolyposis Colorectal Cancer (HNPCC), However, because man y HNPCC families fail to display mutations in known MMR genes, we argued th at changes in other components of the MMR pathway may be responsible. The i ncreasing number of proteins reported to interact in the MMR pathway sugges ts that larger complexes are formed, the composition of which may differ am ong cell types and tissues. In an attempt to identify tissue-specific MMR-a ssociated factors, we employed the yeast two-hybrid system, using the human hMSH2 as bait and a human fetal liver library as prey. We demonstrate that hMSH2 interacts with a human 5'-3' exonuclease 1 (hEXO1/HEX1) and that thi s interaction is mediated through their C-terminal domains. The hMSH6 prote in does not interact with hEXO1 in the two-hybrid system. Dot-blot analysis of multiple tissue RNA revealed that hMSH2 and hEXO1 are coexpressed at hi gh levels in fetal liver as well as in adult testis and thymus. Northern bl ot analysis also revealed that hEXO1/HEX1 is highly expressed in several li ver cancer cell lines as well as in colon and pancreas adenocarcinomas, but not in the corresponding non-neoplastic tissue. (C) 2000 Elsevier Science B.V. All rights reserved.