Analysis of EPC‐1 growth state–dependent expression, specificity, and conservation of related sequences

The transcipt for EPC‐1 (early population doubling level (PDL) cDNA‐1) is induced under conditions of growth arrest due to density‐dependent contact inhibition and/or serum deprivation in early‐passage but not in senescent WI‐38 fibroblasts. We have characterized the EPC‐1 transcript with respect to its cell‐cycle regulation, tissue specificity, and interspecies conservation of related genomic sequences. In low density, quiescent (serum‐deprived), early‐passage fibroblasts that are stimulated to proliferate with fresh serum, steady‐state EPC‐1 transcript levels are steadily reduced until they reach a basal level approximately 24 h after stimulation. However, when early‐passage fibroblasts are made quiescent by both serum deprivation and density‐dependent contact inhibition and then stimulated with serum, steady‐state EPC‐1 transcript levels remain relatively constant throughout a 36 h period following serum stimulation. Senescent WI‐38 cells (>95% life span completed) do not express EPC‐1 under these conditions. We show that differences in the regulation of EPC‐1 transcript levels in early‐passage cells are due to differences in growth state rather than changes in cell densityor contact. We also show that expression of the EPC‐1 transcript is limited to specific cell types and that related genomic sequences are found in all mammalian species examined as well as in the chicken. © 1995 Wiley‐Liss, Inc.