Dexras1 is a novel modulator of adenylyl cyclase

Chau Huynh Nguyen, Purdue University

Abstract

Dexras1/AGS1/RasD1 is a novel member of the Ras superfamily of monomeric G proteins, Studies have implicated a regulatory role for Dexras1 in many pathological conditions including oncogenesis, fetal alcohol syndrome, and impairments of the circadian rhythm. Dexras1 has been shown to target both inhibitory Gαi/o subunits, as well as Gβγ subunits. These results suggest that Dexrasl may have a role in the regulation of adenylyl cyelase by way of the Gi/o subfamily of heterotrimeric G proteins. In the present studies, we examined the effects of Dexras1 on the signaling of two adenylyl cyelase isoforms, adenylyl cyelase type 1 (AC1) and adenylyl cyelase type 2 (AC2) in HEK293 cells. The results of our studies with AC1 suggested that Dexras1 may preferentially target receptor-stimulated Gβγ-dependent signaling pathways in intact cells. Dexras1 did not interfere with the inhibition of AC1 by Gαi/o subunits following the acute stimulation of a Gi/o-coupled receptor. In contrast, Dexras1 significantly impaired receptor-stimulated transactivation of ERK 1/2 and Gβγ-dependent heterologous sensitization of AC1. The ability of Dexras1 to block heterologous sensitization of AC1 was dependent on GTP binding, as a Dexras1 mutant deficient in guanine nucleotide binding (G31V) had no effect on sensitization of AC1. We also examined the effects of Dexras1 on AC2 signaling. Dexras1 was able to abolish Gi/o-coupled receptor-mediated potentiation of AC2 activity following the co-stimulation of a GS- and a G i/o-coupled receptor. These results are consistent with the ability of Dexras1 to interfere with receptor-mediated activation of Gβγ signaling effectors. We also identified a novel role for Dexras1 in modulating AC2 activity by negatively regulating protein kinase C (PKC) signaling. Using the AC2 activator, phorbol 12-myristate 13-acetate (PMA), we showed that Dexras1 abolished PMA-stimulated AC2 activity. The mechanism appeared to be through inhibition of PKC autophosphorylation. Moreover, the role for Dexras1 in regulating PKC was selective for the PKCδ isoform. Additional studies revealed that the effects of Dexras1 required membrane localization and appeared to involve a direct interaction with PKCδ. Collectively, these data provide evidence that Dexras1 may indirectly regulate adenylyl cyclase isofrm by inhibiting Gβγ and PKCδ activity.

Degree

Ph.D.

Advisors

Watts, Purdue University.

Subject Area

Pharmacology

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