NERVE GROWTH-FACTOR INDUCES TRANSCRIPTION OF THE P21 WAF1 CIP1 AND CYCLIN D1 GENES IN PC12 CELLS BY ACTIVATING THE SP1 TRANSCRIPTION FACTOR/

The PC12 pheochromocytoma cell line responds to nerve growth factor (N GF) by gradually exiting from the cell cycle and differentiating to a sympathetic neuronal phenotype. We have shown previously (Yan acid Zif f, 1995) that NGF induces the expression of the p21 WAF1/CIP1/Sdi1 (p2 1) cyclin-dependent kinase (Cdk) inhibitor protein and the G(1) phase cyclin, cyclin D1. In this report, we show that induction is at the le vel of transcription and that the DNA elements in both promoters that are required for NGF-speciiic induction are clusters of binding sites for the Sp1 transcription factor NGF also induced a synthetic promoter with repeated Sp1 sites linked to a core promoter, and a plasmid regu lated by a chimeric transactivator in which the Gal4 DNA binding domai n is fused to the Sp1 transactivation domain, indicating that this tra nsactivation domain is regulated by NGF. Epidermal growth factor, whic h is a weak mitogen for PC12, failed to induce any of these promoter c onstructs. We consider a model in which the PC12 cell cycle is arreste d as p21 accumulates and attains inhibitory levels relative to Cdk/cyc lin complexes. Sustained activation of p21 expression is proposed to b e a distinguishing feature of the activity of NGF that contributes to PC12 growth arrest during differentiation.