P53(LYN) AND P56(LYN) - A NEW SIGNALING PATHWAY IN HUMAN ENDOMETRIUM AND ENDOMETRIAL ADENOCARCINOMAS

OBJECTIVE: To identify specific tyrosine kinases that are involved in endometrial signaling and to study their in vivo expression in normal and abnormal endometrium. We hypothesized that proteins that are diffe rentially expressed would be more likely to be important in regulated cellular events. METHODS: Complementary DNA libraries, constructed fro m human secretory (n = 5) and proliferative (n = 5) endometrial specim ens, were screened with a polyclonal anti-phosphotyrosine antibody. Po sitive clones were sequenced and screened for differential expression using immunoblotting and Northern analysis of samples from proliferati ve and secretory endometrium. The expression of one identified clone, lyn, a Src family member, was characterized further with Western and N orthern blot analyses and immunolocalization. RESULTS: One protein ide ntified by the above method was lyn, a member of the src family of pro tein tyrosine kinases, never before described in the human endometrium . Western blot analysis revealed two forms of lyn protein, p53(lyn) an d p56(lyn), that were most abundant in the late secretory phase. Immun ohistochemistry demonstrated uniform protein expression by all cells i n normal glandular epithelium and suggested a correlation between lyn protein expression and cell differentiation for human endometrial aden ocarcinomas, with markedly elevated levels noted in poorly differentia ted adenocarcinomas compared with well-differentiated tumors (n = 3). Northern hybridization confirmed the presence of the expected 3.5-kb l yn transcript in normal and abnormal endometrium. CONCLUSIONS: Our dat a demonstrate that human cDNA libraries created from different phases of the menstrual cycle can be screened successfully using anti-phospho tyrosine antibodies to identify differentially expressed protein tyros ine kinases. Although p53(lyn) and p56(lyn) expression has been though t of as a predominantly lymphoid-specific tyrosine kinase, we show pro minent expression of lyn protein and mRNA by normal and malignant epit helium of the human endometrium, suggesting a role in endometrial sign aling and human reproduction. Copyright (C) 1997 by the Society for Gy necologic Investigation.