Additional 5′ Exons in the RGS3 Locus Generate Multiple mRNA Transcripts, One of Which Accounts for the Origin of Human PDZ-RGS3

Abstract

Regulators of G-protein signaling (RGS) proteins can be broadly divided into those that consist predominantly of an RGS domain and those that possess an RGS domain along with additional domains. RGS3 fits into both categories, as both short and longer forms exist. Recently, a novel form of mouse RGS3 that possesses a PDZ domain was identified. Here we show that the human PDZ-RGS3 isoform arises from 10 upstream exons along with 6 exons from the previously characterized RGS3. We found that 47,000 nucleotides span the last of the 10 upstream exons and the first exon used from the original cluster of RGS3 exons. These 10 upstream exons encode 398 amino acids, which show strong conservation with those from mouse PDZ-RGS3. In addition, another isoform exists that uses 17 upstream exons, 9 of which overlap with those in PDZ-RGS3, along with the same 6 downstream exons used in PDZ-RGS3. Finally, a short form of human RGS3 arises from an unrecognized RGS3 exon that encodes an amino-terminal 140 amino acids. For each RGS3 isoform, RT-PCR detected specific mRNA transcripts and immunoblot analysis identified specific bands for RGS3 and PDZ-RGS3. RGS3 provides an example of the complex origins of the coding regions of mammalian proteins.Key Words: RGS, RNA splicing, G-protein, genomic amino-terminal region that shares some similarity with a domain in synapsin [5]. Northern blot analysis revealed prominent 1.8-and 3.5-kb RGS3 mRNA transcripts, but also two lessprominent transcripts of 4.2 and 4.5 kb [5]. The 1.8-and 3.5-kb mRNA transcripts presumably encoded short and long versions of RGS3, but the larger transcripts had no protein-coding region assigned to them. An expression vector for a short form of RGS3 (RGS3T or RGS3CT) was created by arbitrarily choosing an internal ATG [5][6][7]. Both forms of RGS3 act as GAPs for G i␣ and G q␣ , but not G s␣ or G 12␣ [8]. Expression of either form of RGS3 inhibits signaling through a variety of GPCRs that use G i␣ and G q␣ to tranduce signals [5][6][7][8][9]. The shorter version of RGS3 in part localizes in the nucleus and its expression promotes apoptosis of Chinese hamster ovary (CHO) cells [10]. The introduction of RGS3 into B-cell lines inhibited CXCR1-and CXCR4-directed cell migration [11,12]. Perhaps accounting for the efficacy of RGS3 as an inhibitor of chemotaxis, it, in contrast to several other RGS proteins, also inhibits signaling by free G ␤1␥2 subunits [13]. Interference with G ␤␥ signaling blocks chemokine-directed migration [14,15]. 861Article doi:10.1006/geno.2002.6773, available online at http://www.idealibrary.com on IDEAL A partial cDNA for the mouse long form of RGS3 and for a short version of RGS3 with a unique N-terminal 21-amino-acid extension [12] have been identified, as well as a cDNA for the purported full-length version of the long form of mouse RGS3 (GenBank acc. no. AK004648). A partial cDNA clone for another isoform of mouse RGS3, which possesses a 398-amino-acid N-terminal extension containing a PDZ domain, was isolated by interaction cloning using t...

RGS3 mediates a calcium-dependent termination of G protein signaling in sensory neurons

“…Studies described here have used dorsal root ganglion (DRG) neurons from embryonic chick to study the mechanisms underlying the initiation of RGS3-dependent signaling (28)(29)(30)(31)(32)(33). In these neurons, the gene encoding RGS3 gives rise to several alternatively spliced transcripts, and we have cloned five variants using library screening methods (GenBank accession nos.…”

Regulation of Smad-Mediated Gene Transcription by RGS3

“…Several isoforms of RGS3 result from an alternative splicing and/or transcription from alternate promoters (Chatterjee et al, 1997;Kehrl et al, 2002). All RGS3 isoforms contain an identical RGS domain that functions as a GTPase-activating protein and an N-terminal region of various lengths, the functions of which are poorly understood.…”

Thinking Outside of the “RGS Box”: New Approaches to Therapeutic Targeting of Regulators of G Protein Signaling: Fig. 1.

“…RGS3 exists as three splice variants; the two longer forms, RGS3L and PDZ-RGS3, contain domains involved in protein-protein interactions (Kehrl et al, 2002). Despite the apparent lack of additional structured domains, several R4 family members have been shown to possess functions beyond GAP activity (for review, see Bansal et al, 2007).…”