ISOLATION AND CHARACTERIZATION OF EPIDERMAL GROWTH FACTOR RELATED PROTEIN

摘要

A cDNA fragment clone of 1583 base pairs with 90-95 % sequence homology to the mouse EGFR and a truncated rat EGFR was isolated. The isolated cDNA lacked the "termination" codon, rapid amplification of cDNA ends (RACE) was applied to obtain the 3'-terminal end. The full-length cDNA revealed 1753 base pairs that contained 227 base pairs of 5' untranslated region and an open reading frame encoding 473 amino acids which showed an 84 % and 91 % homology, respectively, to a rat truncated EGFR and the mouse EGFR. We refer to the product of the newly isolated cDNA as ERRP (EGF-Receptor Related Protein). In Northern-blot analysis with poly A<+> RNA from different rat tissues, ERRP cDNA hybridized strongly to a mRNA transcript of about 1.8 kb. Maximal expression was noted in the small intestine, followed by colon, liver, gastric mucosa and other tissues. Transfection of ERRP cDNA in HCT-116 cells, a colon cancer cell line, markedly inhibits proliferation in monolayer and in soft agar and attenuates EGF-R tyrosine kinase activity. Transfection of ERRP in HCT-116 also delays tumor growth in SCID mice injected with these cells compared to the vector-transfected control cells. On the other hand, proliferation of the vector-transfected control, but not ERRP transfected HCT cells could be stimulated by TGF- alpha (10<-10>M and 10<-9>M). The ERRP cDNA represents a new member of the EGFR gene family, and its protein product plays a key role in modulating the function of EGFR.