Subtraction cloning of growth arrest inducible genes in normal human epithelial cells

Abstract

The purpose of this study was to investigate molecular mechanisms of growth arrest of normal human epithelium. By using a primary outgrowth culture system of normal human ectocervical epithelial cells which undergo density arrest, several known genes and 3 unknown genes, whose expression is induced during growth arrest, were identified. In this report, we characterized one of these novel growth arrest inducible genes, clone 6A1. The size of 6A1 transcript was 1.3 Kb, and the isolated clone was 1,356 bp long and had a putative open reading frame that encodes 309 amino acids (34 Kd), which was consistent with the results of in vitro transcription-translation. In normal human epithelial cells contact inhibition dramatically induced 6A1 expression but serum starvation induced little. And the expression of 6A1 was transiently induced in the early phase of growth arrest. In contrast to normal epithelial cells, normal fibroblast and 2 out of 4 carcinoma cell lines expressed little or no 6A1 mRNA either during contact inhibition or during serum starvation. These results suggested that 6A1 may be important in contact inhibition of normal epithelial cells and loss of its expression may play a role in tumorigenesis.