Cytochrome P450 26C1 (UniProt Q6V0L0; also known as CYP26C1, Cytochrome P450, family 26, subfamily C, polypeptide 1) is encoded by the CYP26C1 (also known as FFDD4) gene (Gene ID 340665) in human. Cytochromes P450 (CYP) proteins are primarily membrane-associated oxidases located either in the inner membrane of mitochondria or in the endoplasmic reticulum where they function as the terminal enzymes in electron transfer chains. In addition to processing endogenous substrates, CYPs also function to metabolize exogenous drugs and potentially toxic chemicals. The human CYP superfamily consisits of 57 genes and more than 59 pseudogenes divided into 18 families and 43 subfamilies. The CYP26 subfamily of enzymes (CYP26A1, CYP26B1/CYP26A2, CYP26C1) are retinoic acid hydroxylases responsible for the inactivation of all-trans-retinoic acid (atRA) to hydroxylated forms, such as 4-oxo-, 4-OH-, and 18-OH-atRA, with 4-oxo-RA being the most common metabolite. All-trans-RA represents the most active form of RA and plays a crucial role in the development of multiple organs via its gene regulatory function. 4-oxo-9-cis-retinoic acid (9-cis-RA) and 4-oxo-13-cis-retinoic acid (13-cis-RA) are two atRA stereo-isomers that also play an important role in RA signalling. Immunohistochemistry staining reveals moderate to strong expression of CYP26A1 and CYP26B1 in colon cancer tissues when compared with normal colonic epithelium, while CYP26C1 was not expressed in either type of colon tissue samples. CYP26C1 gene mutations are linked to focal facial dermal dysplasia 4 (FFDD4), a group of developmental defects characterized by bitemporal or preauricular skin lesions resembling aplasia cutis congenita.
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