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Canonical and noncanonical cAMP‐dependent signaling pathways activated by PACAP in neuroendocrine cells

PACAP initiates cAMP‐dependent cellular responses in neuroendocrine cells via activation of protein kinase A (PKA), i.e. the canonical cAMP pathway. We have adduced evidence for cAMP‐dependent PACAP signaling to the VIP gene in bovine chromaffin cells independent of PKA (Hamelink et al., J. Neurosci. 22:5310, 2002). We have now identified additional gene targets of the noncanonical cAMP signaling pathway in PC12 cells. A core set of forty‐four genes commmonly upregulated >2‐fold at 6 hr in PC12 cells by 100 nM PACAP‐38 (189 transcripts total), or 25 μM forskolin (299 transcripts total) or >1.5‐fold with 500 μM dibutyryl cAMP (247 transcripts total)(n=5–6) were identified on a 31,000 cDNA microarray (NIA, SMUG and BMAP1 clone sets) using two‐color hybridization (see Vaudry et al., J. Neurochem. 83:, 2002; Ravni et al., Regul. Peptides, in press, 2005). Selected transcripts up‐regulated more than 3–5‐fold by PACAP were assessed for PKA‐dependent versus PKA‐independent regulation on the basis of i) inhibition of induction by H89 and KT5720 in PC12 cells, ii) regulation by cAMP signaling in the PKA‐deficient A.126 PC12 cell line, and iii) direct assessment of PKA‐responsive regulation upon forced expression of constitutively active PKA. Surprisingly, a large number of cAMP‐dependent, PKA‐independent genes as well as many cAMP‐dependent, PKA‐dependent ones, contribute to the PACAP‐differentiated PC12 cell transcriptome.