Characterisation of Human Adenylyl Cyclase IX Reveals Inhibition by Ca2+/Calcineurin and Differential mRNA Plyadenylation

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Abstract
The functional diversity of adenylyl cyclases provides for different modes of cyclic AMP signalling in mammals. This study reports the cloning and functional characterisation of a cDNA encoding human adenylyl cyclase IX (ACIX). The data show that human ACIX is a Ca2+/calcineurin‐inhibited adenylyl cyclase prominently expressed in vital organs, including brain, heart, and pancreas. ACIX mRNA was detected in several brain regions, including neocortex, hippocampus, striatum, and cerebellum. By in situ hybridisation, ACIX mRNA was localised to pyramidal and granule cells of the hippocampus, indicating that it is expressed predominantly in nerve cells. Further analysis of ACIX mRNA expression revealed two major forms of ACIX mRNA that arose through tissue‐specific differential mRNA polyadenylation. Taken together, the data show that (a) human ACIX is under inhibitory control by Ca2+ through calcineurin, (b) ACIX may be involved in higher brain functions, and (c) post‐transcriptional regulation of ACIX gene expression is a species‐specific control mechanism that may enhance the versatility of cyclic AMP signalling in humans.