Rhythmic Expression of Adenylyl Cyclase VI Contributes to the Differential Regulation of Serotonin N-Acetyltransferase by Bradykinin in Rat Pineal Glands

Abstract

The rhythmic nocturnal production of melatonin in pineal glands is controlled by the periodic release of norepinephrine from the superior cervical ganglion. Norepinephrine binds to the ␤-adrenergic receptor and stimulates an increase in intracellular cAMP levels, leading to the transcriptional activation of serotonin N-acetyltransferase, which in turn promotes melatonin production. In the present study, we report that bradykinin inhibits basal-and forskolinstimulated adenylyl cyclase activity, norepinephrine-induced cAMP generation, and N-acetyltransferase expression in a calciumdependent manner. These effects were blocked by pretreatment with U73122 (a selective phospholipase C inhibitor), and 1,2-bis(oaminophenoxy)ethane-N,N,N,N-tetraacetic acid (a Ca 2؉ chelator), but not pertussis toxin. The calcium ionophore, ionomycin, inhibited isoproterenol-mediated cAMP generation, similar to bradykinin. Interestingly, the inhibitory effect of bradykinin was evident only during the daytime. At midday, bradykinin inhibited the cAMP level by ϳ50% but markedly stimulated cAMP production (by ϳ50%) at night. Northern blotting and immunoblotting data disclosed circadian expression of calcium-inhibitable adenylyl cyclase type 6. Expression of adenylyl cyclase type 6 was maximal at Zeitgeber Time (ZT) 01 and very low at ZT 13. Our results suggest that bradykinin-induced calcium inhibits melatonin synthesis through the mediation of adenylyl cyclase type 6 expression.

Type VI Adenylyl Cyclase Regulates Neurite Extension by Binding to Snapin and Snap25

“…For example, the level of AC6 is higher in thyroid tumors than normal thyroid tissues (70). AC6 also is actively regulated during circadian rhythms (24). It is important to note that AC6 is unique among members of the AC superfamily, in that it has very low basal enzymatic activity compared to that of other isoforms (48), and it can be inhibited by most of the signaling pathways examined, including those involving calcium, PKA, PKC, and nitric oxide (8,33,44,74).…”

MicroRNA (miRNA) Transcriptome of Mouse Retina and Identification of a Sensory Organ-specific miRNA Cluster

“…For example, adenylyl cyclase VI (ADCY6), a predicted target for miR-182 and miR-96 by PicTar and TargetScan, has a circadian pattern of expression in the pineal body at both the mRNA and protein levels with an apex around ZT5 and nadir around ZT17 (74). These cyclical variations in ADCY6 expression contribute to the differential regulation of AANAT, which encodes serotonin N-acetyltransferase (acetyl-coenzyme A:arylalkylamine N-acetyltransferase), a key enzyme in the melatonin synthesis pathway in pineal gland (74). ADCY6 produces two transcripts, ADCY6_1 (GenBank TM accession number NM_015270) and ADCY6_2 (GenBank TM accession number NM_020983), differing by a 158-nt alternatively spliced exon that contributes to the open reading frame.…”

“…7A) (73). Adcy6 plays important roles in the differential regulation of serotonin N-acetyltransferase (acetylcoenzyme A:arylalkylamine N-acetyltransferase) by bradykinin in rat pineal gland and has a circadian pattern of expression at the levels of mRNA and protein with the apex of expression around ZT5 and a nadir at ZT17 (74). This pattern is the inverse of that of miR-182 (Table 2) as expected if this miRNA contributes to circadian variation of Adcy6 expression ( Table 2, part A).…”

The role of microRNAs (miRNA) in circadian rhythmicity

“…It was found that the mRNA encoding adenylyl cyclase VI (Adcy6), which was shown earlier to be expressed rhythmically (Han et al 2005), is a predicted target (using PicTar and TargetScan) of two putative circadian miRNAs: miR-182 and miR-96. The expression of these miRNAs is in anti-phase to the Adcy6 transcript.…”