ALTERED PROFILE OF TRANSCRIPTION FACTOR-BINDING ACTIVITIES IN SENESCENT HUMAN FIBROBLASTS

Normal eukaryotic cells divide a limited number of times, after which they enter a state of irreversible growth arrest and altered function termed senescence. Cell senescence entails changes in the expression o f growth- and differentiation-specific genes, suggesting that senescen t cells express an altered profile of transcription factors. Nuclear e xtracts were prepared from presenescent (quiescent and growing) and se nescent human fibroblasts (WI-38) and from SV40-immortalized WI-38 cel ls and Y79 human retinoblastoma tumor cells-both of which have escaped senescence. The extracts were assayed for ability to form specific pr otein-DNA complexes with oligonucleotides containing binding sites for the general transcription factors CTF (CAAT-binding transcription fac tor), SP1 (promotor-specific transcription factor-1), and TFIID (trans cription factor-IID) and the more gene-specific factors AP1 (activator protein factor-1), CREBP (cAMP response element-binding protein), GRE BP (glucocorticoid response element-binding protein), NF-kappa B (nucl ear factor kappa B) and OctBP (octamer-binding protein). Two TFIID com plexes and the GREBP, NP-kappa B, and SP1 complexes were similar in pr esenescent and senescent cells. AP1, CREBP, and CTF complexes were red uced in senescent cells. Two activities were more abundant in senescen t cells: OctBP and one TFIID complex. This TFIID complex was present i n quiescent cells, but absent from four human cell lines that lack a f unctional retinoblastoma protein (pRb); both pRb-specific and TFIID-sp ecific antibodies selectively disrupted it. The data suggest that an a ltered profile of transcription factors may specify the senescent phen otype and that pRb may interact with TFIID or a TFIID-associated prote in(s). (C) 1994 Academic Press, Inc.