Abstract
Transcription of arylalkylamine N-acetyltransferase 2 (aanat2) gene leads to formation of AANAT2 - the rate-limiting enzyme in melatonin synthesis pathway in photosensitive fish pineal organ. However, unlike in avian and mammalian pineal gland, there is practically no information on signal transduction pathway(s) involved in regulation of aanat2 gene transcription in the fish pineal organ. Therefore, we investigated the role of important molecular components of signalling via cAMP, cGMP, Ca2+ involving PKA, PKG, PKC, MeK and p38 MAP kinase as well as possible role of serine/threonine phosphatases, CREB and CBP using their specific inhibitors and/or activators in aanat2 gene transcription in the fish pineal organ maintained under in vitro culture-conditions. db-cAMP and db-cGMP stimulated the expression of aanat2 gene. db-cAMP- and cGMP-induced aanat2 gene expression was significantly reduced in the presence of H-89 (specific inhibitor of PKA), KT5823 (specific inhibitor of PKG), chelerythrine chloride (specific inhibitor of PKC), U0126 ethanolate (specific inhibitor of MeK) and SB 202190 monohydrochloride hydrate (specific inhibitor of p38 MAP kinase). Inhibitors of PP1 and PP2A significantly increased aanat2 gene expression as well as significantly reduced cAMP- and cGMP-induced gene transcription, while inhibitor of PP2B had no effect on aanat2 gene expression. Inhibitors of both CREB and CBP-CREB interaction completely blocked cAMP-induced aanat2 gene transcription. Based on these findings, we suggest that cAMP, cGMP and Ca2+ stimulate aanat2 gene transcription via PKA, PKG and PKC, respectively. Further, protein phosphatases and CBP-CREB-CRE pathway are actively involved in regulation of on aanat2 gene expression in the fish pineal organ.
Regulation of ArylalkylamineN-Acetyltransferase-2 (AANAT2, EC 2.3.1.87) in the Fish Pineal Organ: Evidence for a Role of Proteasomal Proteolysis