title: Truncated IRAG variants modulate cGMP-mediated inhibition of human colonic smooth muscle cell contraction.
abstract: Nitric oxide (NO) induces relaxation of colonic smooth muscle cells predominantly by cGMP/cGMP-dependent protein kinase I (cGKI)-induced phosphorylation of the inositol 1,4,5-trisphosphate receptor (IP(3)R)-associated cGMP kinase substrate (IRAG), to block store-dependent calcium signaling. In the present study we analyzed the structure and function of the human IRAG/MRVI1 gene. We describe four unique first exon variants transcribed from individual promoters in diverse human tissues. Tissue-specific alternative splicing with exon skipping and alternative splice donor and acceptor site usage further increases diversity of IRAG mRNA variants that encode for NH(2)- and COOH-terminally truncated proteins. At the functional level, COOH-terminally truncated IRAG variants lacking both the cGKI phosphorylation and the IP(3)RI interaction site counteract cGMP-mediated inhibition of calcium transients and relaxation of human colonic smooth muscle cells. Since COOH-terminally truncated IRAG mRNA isoforms are widely expressed in human tissues, our results point to an important role of IRAG variants as negative modulators of nitric oxide/cGKI-dependent signaling. The complexity of alternative splicing of the IRAG gene impressively demonstrates how posttranscriptional processing generates functionally distinct proteins from a single gene.
authors.affiliation: II. Medizinische Klinik, Technische Universität München, Ismaninger Strasse 22, Munich, Germany.
authors.forename: Alexander von
authors.initials: Av
authors.lastname: Werder
authors.forename: Martina
authors.initials: M
authors.lastname: Mayr
authors.forename: Günter
authors.initials: G
authors.lastname: Schneider
authors.forename: Daniela
authors.initials: D
authors.lastname: Oesterle
authors.forename: Ralph M
authors.initials: RM
authors.lastname: Fritsch
authors.forename: Barbara
authors.initials: B
authors.lastname: Seidler
authors.forename: Jens
authors.initials: J
authors.lastname: Schlossmann
authors.forename: Franz
authors.initials: F
authors.lastname: Hofmann
authors.forename: Michael
authors.initials: M
authors.lastname: Schemann
authors.forename: Hans D
authors.initials: HD
authors.lastname: Allescher
authors.forename: Roland M
authors.initials: RM
authors.lastname: Schmid
authors.forename: Dieter
authors.initials: D
authors.lastname: Saur
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D015153:Blotting, Western; D002460:Cell Line; D003106:Colon / Q000378:metabolism*; D006152:Cyclic GMP / Q000378:metabolism; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism; D020869:Gene Expression Profiling; D006801:Humans; D047468:Immunoprecipitation; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D009119:Muscle Contraction / Q000235:genetics*; D009130:Muscle, Smooth / Q000378:metabolism*; D010750:Phosphoproteins / Q000235:genetics* / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D059368:RNA Isoforms / Q000235:genetics / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection
chemical_list: C485784:IRAG1 protein, human; D008565:Membrane Proteins; D010750:Phosphoproteins; D020033:Protein Isoforms; D059368:RNA Isoforms; D017869:Cyclic GMP-Dependent Protein Kinases; D006152:Cyclic GMP