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.     «

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-sp...     »

Base Sequence, Transfection, Blotting, Western, Amino Acid Sequence, Humans, Molecular Sequence Data, Cell Line, *Gene Expression Profiling, Colon/*metabolism, Cyclic GMP-Dependent Protein Kinases/metabolism, Cyclic GMP/metabolism, Immunoprecipitation, Membrane Proteins/*genetics/metabolism, Muscle Contraction/*genetics, Muscle, Smooth/*metabolism, Phosphoproteins/*genetics/metabolism, Protein Isoforms/genetics/metabolism, Real-Time Polymerase Chain Reaction, Reverse Transcriptase Polymerase Chain Reaction, RNA Isoforms/genetics/metabolism, RNA Processing, Post-Transcriptional     «

Base Sequence, Transfection, Blotting, Western, Amino Acid Sequence, Humans, Molecular Sequence Data, Cell Line, *Gene Expression Profiling, Colon/*metabolism, Cyclic GMP-Dependent Protein Kinases/metabolism, Cyclic GMP/metabolism, Immunoprecipitation, Membrane Proteins/*genetics/metabolism, Muscle Contraction/*genetics, Muscle, Smooth/*metabolism, Phosphoproteins/*genetics/metabolism, Protein Isoforms/genetics/metabolism, Real-Time Polymerase Chain Reaction, Reverse Transcriptase Polymerase Cha...     »