Activation of STAT3 by pituitary adenylate cyclase-activating polypeptide (PACAP) during PACAP-promoted neurite outgrowth of PC12 cells.

Addition of pituitary adenylate cyclase-activating polypeptide (PACAP) into the cultured PC12 cells promoted neurite outgrowth of the cells, indicating cell differentiation. Using DNA macroarray techniques, we have characterized the PC12 cell transcriptome, revealing that several genes were regulated by PACAP. Among many, we focused to investigate whether STAT3 molecule, whose message was up-regulated, might be involved in PACAP signaling. Reverse transcription polymerase chain reaction supported the results obtained by DNA macroarray; PACAP increased gene expression of STAT3, at least up to 24 h, being a maximum 9.5-fold with 3 h-treatment of 1 nM PACAP. Reporter assay analyses demonstrated that PACAP activated STAT3-response promoter, but neither GAS- nor ISRE-response promoters. Enzyme-linked immunosorbent assay revealed that PACAP increased the amount of STAT3 proteins about 30%. Concurrently, phospho-STAT3 Tyr705 was increased in the nuclei by the neuropeptide. Ectopic expression of dominant negative forms of STAT3, which had Tyr705 to phenylalanine substitution, effectively decreased PACAP-promoted neurite extension (55%). During the activation of STAT3, the secretion of interleukin-6 (IL-6) was stimulated by PACAP in a dose-dependent manner. Treatment with IL-6-neutralizing antibody significantly diminished PACAP-activated STAT3 promoter activity and PACAP-induced neurite outgrowth. Thus, our findings have demonstrated that STAT3 is involved in PACAP signaling and function during PC12 cell differentiation by the neuropeptide.