Platelet Gs hypofunction and abnormal morphology resulting from a heterozygous RGS2 mutation

Abstract

Platelet Gs hypofunction and abnormal morphology resulting from a heterozygous RGS2 mutation. J Thromb Haemost 2010; 8: 1594-603.Summary. Background: Regulator of G-protein signaling (RGS) 2 negatively regulates Gs signaling by inhibiting the activation of adenylyl cyclase (AC). RGS2 mRNA contains four translation initiation sites, leading to four isoforms with different abilities to inhibit AC activity; the largest isoform is the most pronounced inhibitor. A role for RGS2 in platelets is not known. Objective: To describe a heterozygous RGS2 mutation (G23D) in three related patients, leading to Gs hypofunction in their platelets, and to study the mechanism behind the effect of the RGS2 mutation on platelet function and morphology. Methods: Gs signaling was studied ex vivo in platelets and in vitro in transfected cells. Translation initiation was evaluated in vitro, and the interaction of wild-type and G23D RGS2 with AC was unraveled via immunoprecipitation. Platelet granule content was analyzed with proteomics. Results: The mutation leads to reduced cAMP production after stimulation of Gscoupled receptors. The largest RGS2 isoforms, with strong AC inhibitor activity, are enriched when the mutation is present, as compared with wild-type RGS2. Moreover, the mutation results in a stronger interaction of RGS2 with AC. G23D RGS2 carriers have enlarged, round platelets with abnormal a-granules. Proteomics of the platelet releasate revealed altered expression of some proteins involved in actin assembly, and carriers seemed to have a reduced platelet shape change. Conclusions: We present the first platelet Gs signaling defect caused by a heterozygous RGS2 variant that results in a unique mutational mechanism, such as the differential use of translation initiation sites resulting in different functional RGS2 isoforms.

Proteolytic degradation of regulator of G protein signaling 2 facilitates temporal regulation of Gq/11 signaling and vascular contraction

“…We began by studying the degradation rates of RGS2 translated from four previously identified alternative in-frame initiation sites at methionine 1, 5, 16, and 33 (Met-1, Met-5, Met-16, Met-33) (Fig. 1, A and B) (31,(42)(43)(44) and to explore the role of the N-terminal region. Which of these alternative translation products are expressed endogenously in cells or tissues remains unclear because of low expression, rapid degradation, or limitations of antibodies used for detection.…”

Advances in our understanding of the molecular basis of disorders of platelet function

“…The complex imprinted gene cluster GNAS1 codes Gsα and genetic defects within this cluster (including an extra‐large stimulatory Gsα isoform (XL‐Gsα)) give rise to a range of disorders associated with a thrombotic phenotype and Gsα hyperfunction (data reviewed in [43]). Finally, platelet Gs hypofunction linked to a heterozygous mutation in a regulator of G‐protein signalling (RGS) protein 2 results in different functional RGS2 isoforms with a stronger (and inhibitory) interaction with AC [44].…”

RGS2: A multifunctional signaling hub that balances brown adipose tissue function and differentiation

“…Although RGS2 has strong selectivity for Gq signaling, it was also shown to regulate Gi and Gs signaling, the latter through a GAP-independent mechanism by directly inhibiting ACs [[32], [33], [34]]. The attenuation of Gs signaling by RGS2 plays a role in platelet formation and signal transduction in olfactory neurons [34,35]; however, the physiological significance of Gs inhibition by RGS2 in metabolism is still largely unknown. Human studies have shown that deregulation of RGS2 is associated with hypertension and susceptibility to metabolic syndrome [36,37].…”