RGCC (regulator of cell cycle) is a multifunctional protein that modulates cell cycle progression and cellular responses across diverse tissue types. RGCC enhances CDK1 activity and regulates mitotic progression, with its deficiency causing abnormal spindle orientation and driving neural stem cells toward asymmetric division, ultimately affecting brain development 1. The protein demonstrates tissue-specific expression patterns, being highly expressed in choriocapillaris endothelial cells where it responds to complement activation and induces apoptosis 2. In cancer contexts, RGCC promotes metastasis by activating PLK1 kinase activity, which phosphorylates AMPKα2 to enhance oxidative phosphorylation and fatty acid oxidation, supporting tumor cell survival during metastasis 3. Notably, RGCC exhibits protective functions in fibrotic diseases, with decreased expression associated with pulmonary fibrosis development 4. RGCC overexpression attenuates TGF-β-induced collagen production by delaying Smad2/3 phosphorylation and modulating STAT1/STAT3 signaling pathways 4. Genetic variants affecting RGCC expression are linked to multiple sclerosis risk through oligodendrocyte-specific enhancer dysregulation 5. The protein's diverse roles span from cell cycle control to tissue homeostasis, making it clinically relevant across neurological, fibrotic, and neoplastic conditions.