{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\n IRAG1 (also known as MRVI1) is a key effector of the nitric oxide/cGMP signaling cascade that modulates intracellular Ca²⁺ release by directly interacting with inositol 1,4,5‐trisphosphate receptors (IP₃Rs) and serving as a substrate for cGMP‐dependent protein kinase I (cGKI). In platelets, IRAG1 is abundantly expressed and is assembled together with cGKIβ and IP₃R1. Phosphorylation of IRAG1 by cGKIβ is essential for the nitric oxide (NO)/cGMP-dependent inhibition of IP₃-induced Ca²⁺ release, thereby restraining fibrinogen receptor activation and platelet aggregation to prevent arterial thrombosis."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "1"}]}, {"type": "t", "text": " In smooth muscle tissues, the interaction between IRAG1 and IP₃R1 is likewise critical; targeted disruption of this interaction abolishes NO/ANP- and cGMP-mediated inhibition of hormone-induced Ca²⁺ mobilization, resulting in impaired relaxation of vascular and gastrointestinal smooth muscles and altered blood pressure regulation."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "2", "end_ref": "4"}]}, {"type": "t", "text": " Moreover, alternative splicing of the IRAG1 gene generates multiple isoforms, some of which (lacking the cGKI phosphorylation and IP₃R1 interaction domains) antagonize cGMP-mediated Ca²⁺ signaling, highlighting the importance of posttranscriptional regulation in fine-tuning smooth muscle tone."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "5"}]}, {"type": "t", "text": " Genetic mutations in IRAG1 have also been implicated in human disease, as a homozygous nonsense mutation in this gene was identified in individuals with early-onset achalasia, thereby emphasizing its role in regulating IP₃R-mediated Ca²⁺ signaling in diverse tissues."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "6"}]}, {"type": "t", "text": " Finally, physical interactions between IRAG1 and cGKIβ, which are mediated by defined charged amino acid motifs, contribute to the correct subcellular localization and specificity of cGKI-dependent signal transduction."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "7"}]}, {"type": "t", "text": " Collectively, these studies demonstrate that IRAG1 is a pivotal modulator of NO/cGMP/cGKI signaling, orchestrating Ca²⁺ dynamics in platelets and smooth muscle cells with critical implications for thrombosis, vascular tone, gastrointestinal motility, and related pathophysiological conditions.\n "}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Melanie Antl, Marie-Luise von Brühl, Christina Eiglsperger, et al. 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"}, {"type": "b", "children": [{"type": "t", "text": "InsP3R-associated cGMP kinase substrate (IRAG) is essential for nitric oxide-induced inhibition of calcium signaling in human colonic smooth muscle."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "J Biol Chem (2004)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1074/jbc.M313365200"}], "href": "https://doi.org/10.1074/jbc.M313365200"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "14729908"}], "href": "https://pubmed.ncbi.nlm.nih.gov/14729908"}]}, {"type": "r", "ref": 5, "children": [{"type": "t", "text": "Alexander von Werder, Martina Mayr, Günter Schneider, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Truncated IRAG variants modulate cGMP-mediated inhibition of human colonic smooth muscle cell contraction."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Am J Physiol Cell Physiol (2011)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1152/ajpcell.00304.2010"}], "href": "https://doi.org/10.1152/ajpcell.00304.2010"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "21865585"}], "href": "https://pubmed.ncbi.nlm.nih.gov/21865585"}]}, {"type": "r", "ref": 6, "children": [{"type": "t", "text": "Katrin Koehler, Dorra Hmida, Jens Schlossmann, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Homozygous mutation in murine retrovirus integration site 1 gene associated with a non-syndromic form of isolated familial achalasia."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Neurogastroenterol Motil (2020)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1111/nmo.13923"}], "href": "https://doi.org/10.1111/nmo.13923"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "32573102"}], "href": "https://pubmed.ncbi.nlm.nih.gov/32573102"}]}, {"type": "r", "ref": 7, "children": [{"type": "t", "text": "Darren E Casteel, Gerry R Boss, Renate B Pilz "}, {"type": "b", "children": [{"type": "t", "text": "Identification of the interface between cGMP-dependent protein kinase Ibeta and its interaction partners TFII-I and IRAG reveals a common interaction motif."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "J Biol Chem (2005)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1074/jbc.M507021200"}], "href": "https://doi.org/10.1074/jbc.M507021200"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "16166082"}], "href": "https://pubmed.ncbi.nlm.nih.gov/16166082"}]}]}]}