The laboratory has demonstrated that recombinant(r) gamma-interferon (gIFN) phorbol esters (PMA) and tumor necrosis factor (TNF) inhibit human endothelial cell proliferation and r-g IFN induces a loss of receptors on the endothelial cell surface for HBGF-I. Likewise, the cumulation of population doublings (CPC>50) by in vitro age also results in a loss of response to HBGF-I but with an apparent conservation of the HBGF-I receptor at endothelial cell quiescence is related to senescence induced quiescence. Subsequently, we have demonstrated by high resolution comparative 2D gel analysis the expression of senescence-specific polypeptides by human endothelial cells. Interestingly, gIFN, PMA but not TNF invert the expression of a few of these senescence-specific polypeptides in senescent populations of human endothelial cells. These data argue that in in vitro age is a determine their identity. In addition, we have demonstrated that senescent cells express unique translatable mRNAs and thus would like to determine if we can identify genes which are unique to human endothelial cell age in vitro. Lastly, we have constructed a senescence human endothelial cDNA library in lambda gt10 and have isolated 12 cDNA clones by subtraction hybridization. Thus, we would like to further characterize the structure of the senescence-specific polypeptides observed by 2D gel analysis and independently characterize the putative senescence-specific cDNA clones in an attempt to provide a structural basic for the cellular processes during in vitro aging.