| CIRP (cold-inducible RNA‑binding protein) is a small stress-responsive RBP containing an N‑terminal RNA recognition motif and a C‑terminal RG/RGG-rich regulatory domain, originally identified as a protein induced by mild hypothermia and now recognized as a general vertebrate stress factor that coordinates post-transcriptional control of survival, proliferation and inflammatory pathways. The modular structure allows specific binding to AU‑rich and other elements in 3′‑UTRs via the RRM, while the arginine–glycine–glycine domain undergoes phosphorylation and methylation that determine nuclear–cytoplasmic shuttling and recruitment into stress granules, gating access of CIRP to subsets of target transcripts under different stress conditions. Under cold shock, UV radiation, hypoxia and infection, CIRP expression increases through self-transcriptional activation of alternative promoters, and the protein relocates from nucleus to cytoplasm where it stabilizes specific mRNAs and can either repress or enhance their translation, acting as a fine-tuner of stress-responsive gene expression rather than a simple on/off switch. Identified targets include transcripts encoding DNA repair, redox and survival factors; for example, CIRP binds 3′‑UTRs of RPA2 and TXN to stabilize their mRNAs and support genotoxic stress responses and antioxidant capacity, contributing to suppression of apoptosis and preservation of cytoskeletal integrity under moderate stress. CIRP also promotes assembly of stress granules when overexpressed, joining stalled translation initiation complexes and other RBPs in cytoplasmic aggregates that transiently store and triage mRNAs during environmental challenges, and its RG domain is required for both nuclear export and efficient SG recruitment. In cell-cycle control, CIRP modulates translation of the CDK inhibitor p27^Kip1 via binding to AU‑rich elements, inducing p27 production and contributing to cold-induced suppression of cell proliferation and controlled cell-cycle exit. In the heart, CIRP acts as an mRNA stabilizer for phosphodiesterase 4B and 4D transcripts in sinoatrial node cells, maintaining PDE4 expression, restraining cAMP levels and preventing excessive heart rate acceleration in response to β‑adrenergic stress; CIRP knockout animals show exaggerated tachycardic responses, highlighting a role in cardiac electrophysiological plasticity and stress adaptation. In the central nervous system, CIRP has biphasic roles depending on localization: nuclear and cytoplasmic CIRP supports neuronal survival and synaptic function by stabilizing key transcripts, whereas extracellular CIRP released as a DAMP engages pattern-recognition receptors and drives neuroinflammation, contributing to pathology in conditions such as ischemia and neurodegeneration. Extracellular CIRP more broadly has emerged as a proinflammatory mediator in sepsis and cancer-related inflammation, where it binds receptors such as TLR4 or Mincle, amplifies cytokine production and modulates immune-cell recruitment, adding an immunomodulatory dimension to its intracellular RBP functions. |
