Characterization of novel regulatory properties of adenylate cyclase type nine

Medhane G Cumbay, Purdue University

Abstract

The cyclic AMP signaling pathway is present in nearly all cells and controls a number of cellular processes such as cell growth, differentiation, and neuronal plasticity. Adenylate cyclases (EC 4.6.1.1) produce the second messenger cyclic AMP in response to a wide range of signal transduction pathways. To date, nine membrane-bound members of the mammalian adenylate cyclase family (AC1–9) have been identified. Although all adenylate cyclase isoforms are activated by the GTP bound α subunit of Gs (Gαs), each isoform displays complex and distinctive regulatory features. AC9, the most recent of the membrane-bound adenylate cyclases to be identified, is a unique member of the mammalian adenylate cyclase family that exhibits relative insensitivity to forskolin stimulation and is the most divergent in sequence of all the isoforms. AC9 is expressed widely in the central nervous system as well as in other major organs. Of particular interest is the relative abundant expression of AC9 transcripts and protein in the hippocampus, an important region for some forms of learning and memory. Understanding the regulatory features of AC9 is essential to interpreting and manipulating cyclic AMP responses in these tissues. Two modes of regulation previously described for AC9 include stimulation by Gαs and inhibition of basal AC9 activity by Ca2+/calcineurin; however, it is likely that AC9 responds to wider range of regulatory factors in manner similar to that of other adenylate cyclase isoforms. This thesis addresses the hypothesis that AC9 regulation is complex and that additional modes of regulation exist for this isoform . The results of this work demonstrate that AC9 activity, as hypothesized, can be modulated by factors previously unrevealed. These novel regulatory features of AC9 include inhibition of Gαs-stimulated activity by Gi/o proteins and novel PKC isoforms, and CaM-kinase II potentiation of Gαs-stimulated activity. Additional studies also revealed that the glycosylation state of AC9 can selectively influence its regulation by Gαs without altering regulation by Gi/o or novel PKCs. Combined, the work reported in this thesis demonstrates the complex regulatory features of AC9, and identifies a regulatory feature of adenylate cyclases that is unique to AC9, CaM-kinase II potentiated activity.

Degree

Ph.D.

Advisors

Watts, Purdue University.

Subject Area

Pharmacology

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