Keratin, type II cytoskeletal 8 (UniProt: P05787; also known as Cytokeratin-8, CK-8, Keratin-8, K8, Type-II keratin Kb8) is encoded by the KRT8 (also known as CYK8) gene (Gene ID: 3856) in human. Cytokeratins belong to a diverse group of intermediate filaments that participate in differentiation and maintain the structural integrity of epithelial cells. Cytokeratins share a common structural organization: a central alpha-helical rod domain flanked by head and tail domains. An important unique feature of cytokeratins is their epithelial cell-type-specific expression. CK8 is expressed in abundance in the epithelia of colon, bladder, ileum, and stomach. It is a type II, neutral to basic protein that together with cytokeratin-19 (KRT19) helps to link the contractile apparatus to dystrophin at the costameres of striated muscle. CK-8 can undergo phosphorylation on three major serine residues: Serine 23, 431, and 73. Serine 23 is shown to be highly conserved in all type II keratins. Phosphorylation at Serine 73 is reported to increase during cellular stress. However, under normal conditions serine 73 remains largely dephosphorylated. It can also undergo O-glycosylation in a cell cycle-dependent manner and glycosylation increases its solubility and reduces stability by inducing proteasomal degradation. CK8 expression has been correlated with malignancy in leukoplakia and carcinomas of the head and neck and its expression has been observed in all non-small-cell lung cancers.