Keratin, type I cytoskeletal 4 also known as cytokeratin-4 (CK-4) or keratin-4 (K4) is a protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

 that in humans is encoded by the KRT4 gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

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Keratin 4 is a type II cytokeratin

Type II cytokeratin

Type II keratins constitutes the Type II intermediate filaments of the intracytoplasmatic cytoskeleton, which is present in all mammalian epithelial cells...

s. It is specifically found in differentiated layers of the mucosal and esophageal epithelia together with keratin 13

Keratin 13

Keratin 13 is a protein that in humans is encoded by the KRT13 gene.Keratin 13 is a type I cytokeratin, it is paired with keratin 4 and found in the suprabasal layers of non-cornified stratified epithelia...

. Mutations in the genes encoding this protein have been associated with White Sponge Nevus

White sponge nevus

White sponge nevus , also known as Cannon's disease, Hereditary leukokeratosis of mucosa and White sponge nevus of Cannon, is an autosomal dominant skin condition...

, characterized by oral, esophageal

Esophageal

Esophageal can refer to:* The esophagus* Esophageal arteries* Esophageal glands...

, and anal

Anus

The anus is an opening at the opposite end of an animal's digestive tract from the mouth. Its function is to control the expulsion of feces, unwanted semi-solid matter produced during digestion, which, depending on the type of animal, may be one or more of: matter which the animal cannot digest,...

 leukoplakia

Leukoplakia

Leukoplakia is a clinical term used to describe patches of keratosis. It is visible as adherent white patches on the mucous membranes of the oral cavity, including the tongue, but also other areas of the gastro-intestinal tract, urinary tract and the genitals. The clinical appearance is highly...

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