Herpesvirus quiescence in neuronal cells IV: virus activation induced by pituitary adenylate cyclase-activating polypeptide (PACAP) involves the protein kinase A pathway.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a naturally occurring peptide found in the central nervous system that plays a role in somatosensory processing and activation of protein kinase A (PKA) and protein kinase C (PKC). Because activation of PKA or PKC results in reactivation of HSV-1 from latently infected embryonic neuronal cells, PACAP was used to evaluate HSV-1 activation from quiescently infected (QIF)-PC12 cells. Our studies demonstrate that physiologically relevant concentrations of PACAP38 and PACAP27 induce HSV-1 activation from QIF-PC12 cell cultures in a dose-dependent fashion. PACAP-induced activation of virus was significantly impaired by the PKA-inhibitor, H-89 (20 microM), whereas treatment with the PKC-inhibitor, GF109203X (1 microM), was without affect. Additionally, direct activation of PKA with cAMP analogs, 8-(4-chlorophenylthio)- and dibutyryl-cAMP, only partially mimicked the effect of PACAP on virus activation. Taken together, PACAP induced HSV-1 activation from QIF-PC12 cells involves the PKA and possibly cAMP-independent pathways. This report is the first to demonstrate that PACAP induces HSV-1 activation from a quiescent state and that this in vitro cell model is useful for studying early inductive events that lead to virus production from quiescence.