Cloning and characterization of a novel regulator of G protein signalling in human platelets

In an effort to understand the modulation of G protein-coupled receptor (GPCR)-mediated signalling in platelets, we sought to identify which regulators of G protein signalling proteins (RGSs) are present in human platelets. Using degenerate oligonucleotides, we performed RT-PCR with human platelet and megakaryocytic cell line RNA. In addition to confirming the presence of several known RGS transcripts, we found a novel RGS domain-containing transcript in platelet RNA. Northern blot analysis of multiple human tissues indicates that this transcript is most abundantly expressed in platelets compared to other tissues examined. Full-length cloning of this novel RGS, which we now tern RGS 18, demonstrates that this transcript is predicted to encode a 235-amino acid protein that is most closely related to RGS5 (46% identity) and that has similar to 30-40% identity to other RGS proteins. RGS 18 is expressed in platelet, leukocyte, and megakaryocyte cell lines and binds to endogenous G(alphai1), G(alphai2), G(alphai3), and G(alphaq) but not G(alphaz), G(alphas) or G(alphai2) in vitro. (C) 2002 Elsevier Science Inc. All rights reserved