RCCD1 (RCC1 domain containing 1) is a multi-functional protein with roles in nuclear and mitochondrial processes. In the nucleus, RCCD1 regulates transcriptional repression of satellite repeats through H3K36 methylation modulation with KDM8, and participates in mitotic spindle organization and chromosome 15 1. RCCD1 modulates cytoskeletal microtubule stability by regulating alpha-tubulin acetylation, promoting cell migration and TGF-β-induced epithelial-to-mesenchymal transition (EMT) 2. Notably, RCCD1 localizes to the mitochondrial matrix where it interacts with MICOS and mitochondrial DNA to regulate oxidative phosphorylation and reactive oxygen species production, with upregulation under hypoxic conditions favoring cancer cell survival 3. RCCD1 expression is transcriptionally regulated by E2F1 in colorectal cancer 4. Clinically, RCCD1 is dysregulated across multiple cancers: overexpression associates with poor prognosis in lung cancer 2, breast cancer 3, and colorectal cancer 4. Genetic variants regulating RCCD1 methylation show protective effects against pancreatic cancer 5, while genetically predicted RCCD1 expression associates with pancreatic cancer risk 6. RCCD1 is also identified as a biomarker in thin endometrium associated with abnormal immune infiltration 7, and altered in schizophrenia-related placental pathology 8.