Cooperation of Spl and p300 in the induction of the CDK inhibitor p21(WAF1/CIP1) during NGF-mediated neuronal differentiation

Addition of nerve growth factor (NGF) to PC12 cells promotes neuronal diffe rentiation while inhibiting cell proliferation. In order to understand how NGF exerts its antimitogenic effect during differentiation, we have studied the mechanism by which this factor activates the promoter of the CDK inhib itor p21(WAF1/CIP1). The minimal region of the p21 promoter required for th e NGF-induction was mapped to a contiguous stretch of 10 bp located 83 base s upstream of the transcription initiation site, This GC-rich region was sh own to interact specifically with the transcription factor Spl and the rela ted protein Sp3, in either exponentially-growing or NGF-treated PC12 cells, The addition of NGF resulted in an accumulation of the transcriptional co- activator p300 in complexes associated with the NGF-responsive region, Tran scriptional activity of Sp1, Sp3 and p300 was specifically induced by NGF i n a Gal4-fusion assay, indicating that induction of p21 during neuronal dif ferentiation may involve regulation of the activity of these factors by NGF , Furthermore, p300 was able to act as a co-activator for Sp1-mediated tran scriptional activation in PC12 cells, suggesting that p300 and Spl may coop erate in activating p21 transcription during the withdrawal of neuronal pre cursors from the cell cycle. This hypothesis is supported by experiments sh owing that p300 and Spl form complexes in PC12 cells.