{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\nPirh2 is a p53‐induced RING-H2 ubiquitin ligase that plays a pivotal role in controlling cell growth by orchestrating the stability of key regulatory proteins. Acting independently of Mdm2, it physically interacts with p53 to promote its ubiquitination and consequent proteasomal degradation—thereby tempering p53-mediated anti‐proliferative responses—and similarly targets the cyclin-dependent kinase inhibitor p27(Kip1) to facilitate cell cycle progression. Elevated Pirh2 levels detected in lung tumors further underscore its impact on downregulating tumor suppressor functions, while studies of related RING-H2 proteins such as ARNIP emphasize the broader significance of this family in regulating transcription factor interactions and cellular proliferation."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "5"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nIn addition to its impact on tumor suppressor pathways, Pirh2 contributes crucially to the maintenance of genomic stability and the regulation of DNA damage responses. It monoubiquitinates translesion synthesis polymerase eta (PolH), impairing its association with PCNA and its capacity to bypass UV-induced DNA lesions. Pirh2 also mediates the polyubiquitination and degradation of checkpoint kinase CHK2—a modification that is finely tuned by deubiquitylating enzymes—to modulate cell cycle checkpoint activity. Moreover, by ubiquitinating the p53 family member p73 with intricate linkage patterns, Pirh2 regulates p73-dependent transcription and governs cell cycle arrest outcomes."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "6", "end_ref": "8"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nRecent investigations have expanded the functional repertoire of Pirh2 to include the modulation of chromatin and neuronal integrity. Its interaction with histone deacetylase HDAC2 inversely correlates with HDAC2 protein levels in tumors, suggesting an epigenetic dimension to its regulatory influence. In neuronal cells, stabilization of G-quadruplex DNA structures has been linked to increased Pirh2 expression that not only promotes the formation of DNA double-strand breaks but also disrupts the activity of helicases like DDX21. Furthermore, in experimental models of Alzheimer’s disease, elevated Pirh2 is associated with enhanced amyloid-β aggregation, dysregulated endoplasmic reticulum stress, impaired mitochondrial function, and consequent neuronal damage, whereas its silencing mitigates these pathological hallmarks."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "9", "end_ref": "12"}]}, {"type": "t", "text": "\n"}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Roger P Leng, Yunping Lin, Weili Ma, et al. 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