MEDIATION OF NGF SIGNALING BY POSTTRANSLATIONAL INHIBITION OF HES-1, A BASIC HELIX-LOOP-HELIX REPRESSOR OF NEURONAL DIFFERENTIATION

The induction of neurite outgrowth by NGF is a transcription-dependent process in PC12 cells, but the transcription factors that mediate thi s profess are not known. Here we show that the bHLH transcriptional re pressor HES-1 is a mediator of this process. Inactivation of endogenou s HES-1 by forced expression of a dominant-negative protein induces ne urite outgrowth in the absence of NGF and increases response to NGF. I n contrast, expression of additional wild-type HES-1 protein represses and delays response to NGF. Endogenous HES-1 DNA-binding activity is post-translationally inhibited during NGF signaling in vivo, and phosp horylation of PKC consensus sites in the HES-1 DNA-binding domain inhi bits DNA binding by purified HES-1 in vitro. Mutation of these sites g enerates a constitutively active protein that strongly and persistentl y blocks response to NGF. These results suggest that post-translationa l inhibition of HES-1 is Both essential for and partially mediates the induction of neurite outgrowth by NGF signaling.