NH2-terminal amino acid sequence of the pS2 protein produced and secreted by human gastric cancer cells, MKN-45, was determined to be identical to that of MCF-7 cells. A clone encoding pS2 protein was isolated from the cDNA library constructed from MKN-45 cells. The nucleotide sequence was identical to that of pS2 cDNA previously isolated from human breast cancer cells, MCF-7, except for one nucleotide in the 3' untranslated region. Thus, in this cell line, the pS2 gene product is translated and secreted as in MCF-7 cells. RNA blot hybridization analysis revealed that pS2 gene was expressed well in two (MKN-45 and KATO-III; derived from poorly differentiated adenocarcinoma) but not in three cell lines (MKN-1, MKN-28 and MKN-74; from well differentiated adenocarcinoma), suggesting that expression of the pS2 gene depends on the state of cell differentiation. These results suggest that pS2 is expressed in human gastric cancer cells in an estrogen-independent manner and is possibly associated with the malignant state of cells.
