| Cold-inducible RNA-binding protein (CIRP), encoded by the CIRBP gene, belongs to the cold-shock protein group and contains an N-terminal RNA recognition motif together with a C-terminal arginine–glycine–glycine (RGG) rich domain that supports RNA binding and interaction with cytoplasmic ribonucleoprotein assemblies under stress. CIRP expression increases after exposure to moderate hypothermia, UV irradiation, hypoxia and oxidative or osmotic stress, and the protein initially localizes in the nucleus before undergoing methylation-dependent translocation to the cytoplasm, where it accumulates in stress granules containing stalled translation initiation complexes. Arginine methylation within the RGG motifs is required for exit from the nucleus and recruitment into stress granules, and both the RRM and RGG domains can independently drive migration to these granules, linking domain structure with spatial control of RNA–protein complexes during stress. CIRP binds specifically to motifs in the 3′-untranslated regions of target mRNAs, including stress-responsive transcripts such as RPA2 and TXN, and this interaction modulates mRNA stability and translation efficiency, with the C-terminal RG-rich domain carrying translational repression activity demonstrated by RNA-tethering experiments. Under genotoxic or environmental stress, CIRP stabilizes transcripts involved in cell survival and acts as a translational activator for selected mRNAs, while at the same time acting as a translational repressor when tethered to reporter mRNAs, indicating context-dependent regulation of protein synthesis that is determined by its binding position and association with stress granule components. Overexpression induces robust assembly of stress granules even without global changes in CIRP expression, and stress granule recruitment occurs independently of TIA-1, revealing a pathway in which CIRP nucleates or joins granules through mechanisms distinct from previously characterized SG scaffolds. Post-translational regulation includes phosphorylation by CK2, GSK3A and GSK3B, with GSK3B-mediated phosphorylation enhancing RNA-binding activity to the TXN 3′-UTR following UV exposure, integrating kinase signaling with selective targeting of stress-related transcripts. Through its effects on mRNA stability, translation and stress granule assembly, CIRP contributes to suppression of cell proliferation at low temperature and to protection in genotoxic stress responses, serving as a post-transcriptional regulator that adjusts protein output and survival pathways when cells encounter environmental or DNA damage stressors. Dysregulated CIRP activity and extracellular release, including exosome-derived CIRP described in broader literature, associate with inflammatory conditions and cancer, but the core mechanistic features that attract research interest are its cold-inducible expression, structured RRM–RGG architecture, methylation- and phosphorylation-dependent trafficking and its role in organizing stress granules to control translation of defined 3′-UTR-bearing survival and stress-response transcripts. |
