Cytoskeleton Proteins

Cytokeratin-19 (Keratin, type I cytoskeletal 19) is involved in the organization of myofibers. Cytokeratin-19 together with KRT8, helps link the contractile apparatus to dystrophin at the costameres of striated muscle. Cytokeratin-19 is expressed in a defined zone of basal keratinocytes in the deep outer root sheath of hair follicles. Cytokerating-19 is also observed in sweat gland and mammary gland ductal and secretory cells, bile ducts, gastrointestinal tract, bladder urothelium, oral epithelia, esophagus, ectocervical epithelium.

Cytokeratin-18 (Type I cytoskeletal keratin 18) is involved in the uptake of thrombin-antithrombin complexes by hepatic cells. Defects in cytokeratin-18 are a cause of cirrhosis (CIRRH).

Cytokeratins are proteins of keratin-containing intermediate filaments found in the intracytoplasmic cytoskeleton of epithelial tissue. There are two types of cytokeratins: the acidic type I cytokeratins and the basic or neutral type II cytokeratins. Cytokeratins are usually found in pairs comprising a type I cytokeratin and a type II cytokeratin. Immunohistochemical detection of cytokeratins is of immense value in tumor cell diagnosis and identification.

Vimentin is the major subunit protein of the intermediate filaments of mesenchymal cells. Vimentin is involved in the intracellular transport of proteins between the nucleus and plasma membrane. Vimentin is also implicated in steroid synthesis via its role as a storage network for steroidogenic cholesterol containing lipid droplets. Immunohistochemical staining for vimentin is characteristic of sarcomas (or neural, muscle, and fibroblast origin) as compared to carcinomas which are generally negative.

CK1 (Cytokeratin-1) is an intermediate filament protein. CK1 regulates the activity of kinases such as PKC and SRC via binding to integrin beta-1 (ITB1) and the receptor of activated protein kinase C (RACK1/GNB2L1). Defects in CK1 are a cause of bullous congenital ichthyosiform erythroderma, also known as epidermolytic hyperkeratosis (EHK) or bullous erythroderma ichthyosiformis congenita of Brocq. BCIE is an autosomal dominant skin disorder characterized by widespread blistering and an ichthyotic erythroderma at birth that persists into adulthood.