Putative role for EPC‐1/PEDF in the G0 growth arrest of human diploid fibroblasts

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Abstract
EPC‐1/PEDF expression is closely associated with reversible growth arrest in normal human diploid fibroblast‐like (HDF) cells and is diminished with proliferative senescence in vitro. EPC‐1 expression in HDF cells is induced under conditions of density‐dependent contact inhibition and growth factor deprivation. Antiserum generated against EPC‐1 recognizes a secreted protein of approximately 50 kDa from medium conditioned by early passage HDF cells, but not from senescent cells. The addition of EPC‐1 antiserum to early population doubling level (PDL) cultures near the plateau phase of growth significantly increases the number of cells entering DNA synthesis. Affinity purified EPC‐1 antibodies alone enhance the ability of near plateau‐phase early PDL WI‐38 cells to synthesize DNA by as much as threefold. Further, the addition of recombinant EPC‐1 (rEPC‐1) to logarithmically growing cells resulted in a marked decrease in the ability of these cells to enter DNA synthesis. We also demonstrate the loss of EPC‐1 expression in WI‐38 and IMR‐90 HDF cell lines with both senescence and simian virus 40 (SV40) transformation. The loss of EPC‐1 expression with SV40 transformation occurs at the level of steady‐state mRNA and protein accumulation with genomic EPC‐1 sequences grossly intact. Taken together, these results suggest that EPC‐1 may play a role in the entry of early passage fibroblasts into a G0 state or the maintenance of such a state once reached.

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