Pituitary Adenylate Cyclase‐Activating Polypeptide Triggers Dual Transduction Signaling in CATH.a Cells and Transcriptionally Activates Tyrosine Hydroxylase and c‐fos Expression

: We used a catecholaminergic neuron‐like cell line (CATH.a cells) as a model system to investigate the likelihood that pituitary adenylate cyclase‐activating polypeptide (PACAP) may participate in the regulation of specific gene expression in catecholaminergic neurons. Analysis by reverse transcriptase‐PCR amplification revealed the presence in these cells of type I PACAP receptors, with a short isoform, together with a heavier so‐called Hop splice variant. PACAP38 and PACAP27 enhanced, in a dose‐dependent manner, both cyclic AMP formation and phosphoinositide breakdown, with EC50 values of, respectively, 0.6 × 10−10 and 2 × 10−9M. These peptides, in addition, also elevated [Ca2+]i by mobilizing intracellular calcium pools. Vasoactive intestinal peptide (VIP) was ∼1,000‐fold less potent in stimulating cyclic AMP (with EC50 = 2 × 10−7M) and failed to change the turnover of phosphoinositides and to alter [Ca2+]i. Both forms of PACAP, as well as forskolin, stimulated transcriptional induction of tyrosine hydroxylase (TH) and c‐fos promoters fused to a chloramphenicol acetyltransferase (CAT) reporter gene in transiently transfected cells (p < 0.01 vs. controls). Induction of CAT activity linked to both TH and c‐fos promoters was obliterated upon coexpression of a dominant inhibitory mutant (Mt‐RAB) of cyclic AMP‐dependent protein kinase. We conclude that CATH.a cells do express functional PACAP type I receptors, the activation of which impinges on TH and c‐fos transcription according to a process that is primarily dependent on the cyclic AMP‐PKA pathway.