Journal of Thrombosis and Haemostasis vol:8 issue:7 pages:1594-1603
Summary Background: Regulator of G protein signaling 2 (RGS2) negatively regulates Gs signaling by inhibiting 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 as most pronounced inhibitor. A role for RGS2 in platelets is not known. Objective: We describe a heterozygous RGS2 mutation (G23D) in three related patients, leading to a Gs hypofunction in their platelets. The mechanism behind the effect of the RGS2 mutation on platelet function and morphology was studied. 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 Gs-coupled receptors. The largest RGS2 isoforms with strong AC inhibitor activity are enriched when the mutation is present, compared to wild type RGS2. Moreover, the mutation results in a stronger interaction of RGS2 with AC. RGS2-G23D carriers have enlarged, round platelets with abnormal alpha granules. Proteomics of the platelet releasate revealed an 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 due to a heterozygous RGS2 variant that results in a unique mutational mechanism as the differential use of translation initiation sites resulting in different functional RGS2 isoforms.