TYPE-VIII ADENYLYL-CYCLASE - A CA2+ CALMODULIN-STIMULATED ENZYME EXPRESSED IN DISCRETE REGIONS OF RAT-BRAIN/

A cDNA that encodes type VIII adenylyl cyclase has been isolated from two rat brain libraries. The open reading frame encodes a 1248-amino a cid protein predicted to have two sets of six transmembrane spans and two putative nucleotide binding domains as is characteristic of other mammalian adenylyl cyclases. Two type VIII messages are detected in ra t brain with estimated sizes of 5.5 and 4.4 kilobases. In situ hybridi zation indicates that the type VIII messages are most abundantly expre ssed in the granule cells of the dentate gyrus, the pyramidal cells of hippocampal fields CA1-CA3, the entorhinal cortex, and the piriform c ortex. Hybridization is also detected in the neocortex, the amygdaloid complex, and regions of the thalamus and hypothalamus. Stable express ion of the type VIII cDNA in human embryonal kidney cells leads to the appearance of a novel 165-kDa glycoprotein in the membrane fraction. Stimulation of these cells with agents that increase intracellular Ca2 + results in up to 43-fold increases in cAMP accumulation over that of control cells transfected with the expression vector. Addition of iso proterenol alone does not lead to type VIII-specific effects in intact cells. Adenylyl cyclase activity in membranes prepared from type VIII -transformed cells is stimulated up to 40-fold by the addition of Ca2/calmodulin (EC(50) = 53 nM calmodulin). The addition of activated rec ombinant alpha subunit of G(s) synergistically increases the Ca2+/calm odulin-stimulated activity. A possible role for type VIII adenylyl cyc lase in long-term potentiation is discussed.