Possible implication of the transcriptional regulator Id3 in PACAP-induced pro-survival signaling during PC12 cell differentiation

PACAP inhibits cell proliferation and promotes cell survival and neurite outgrowth of pheochromocytoma PC12 cells. Transcriptome analysis of PACAP-treated PC12 cells allowed to identify potential genes implicated in this differentiation process. Among the genes whose expression is up-regulated by PACAP, we identified the Inhibitor of DNA binding 3 (Id3). Id3 is a member of the helix-loop-helix (HLH) family of transcription factors which acts as a negative dominant inhibitor of basic HLH factors. Time-course studies revealed that Id3 is an early PACAP response gene (8-fold after 1 h of stimulation), and that the up-regulation of its expression persists over 12 h after the onset of PACAP treatment. The stimulatory effect of PACAP on Id3 mRNA levels was mimicked by adenylate cyclase/PKA activators like forskolin and dibutyryl cyclic AMP. Moreover, PACAP-induced Id3 gene expression was inhibited by phosphatidylinositol 3′-OH-kinase and p38 MAP kinase blockers. Northern blot analysis of Id3 distribution in rat tissues showed a strong expression of this gene in the adrenal medulla. Overexpression of Id3 increased the number of living PC12 cells, in basal condition and after exposure to oxidative stress. These results indicate that Id3 is a cAMP-responsive gene whose up-regulation could be involved in PACAP-induced pro-survival signaling during sympathoadrenal cell differentiation.