Regulation of EPC-1/PEDF in normal human fibroblasts is posttranscriptional

The EPC-1 (early population doubling level cDNA-1) gene, also known as pigm ent Epithelium-derived factor, encodes a protein belonging to the serine pr otease inhibitor (serpin) superfamily that has been reported to inhibit ang iogenesis and proliferation of several cell types. We have previously repor ted that the EPC-1 mRNA and the secreted EPC-1 protein are expressed at lev els more than 100-fold higher in Early passage, G(0), WI-38 cells compared to Either proliferating or senescent WI-38 fibroblasts. To examine the mole cular mechanisms that regulate changes in EPC-1 gene expression in WI-38 ce lls, we isolated and characterized the human EPC-1 gene and determined the mRNA cap site. Transcriptional assays showed no change in the transcription rates of EPC-1 between young proliferating, quiescent, and senescent WI-38 cells. These results suggest posttranscriptional regulation of the EPC-1 g ene. Reverse transcriptase polymerase chain reaction measurements (of hnRNA ) indicate regulation at the hnRNA level. The regulation of the EPC-1 gene at the level of hnRNA can explain the observed slow increase in the steady- state EPC-1 mRNA levels when cells become quiescent. The reduction of EPC-1 mRNA levels that occurs when cells exit G(0), and are induced to prolifera te can be accounted for by a reduction of the EPC-1 mRNA stability in stimu lated cells as compared to quiescent cells. (C) 2000 Wiley-Liss. Inc.