Keratin 19
Keratin, type I cytoskeletal 19 also known as cytokeratin-19 (CK-19) or keratin-19 (K19) is a 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 KRT19 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...

. Keratin 19 is a type I keratin.


Keratin 19 is a member of the keratin
Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...

 family. The keratins are intermediate filament proteins responsible for the structural integrity of epithelial cells and are subdivided into cytokeratins and hair keratins.

Keratin 19 is a type I keratin. The type I cytokeratins consist of acidic proteins which are arranged in pairs of heterotypic keratin chains. Unlike its related family members, this smallest known acidic cytokeratin
Cytokeratins are proteins of keratin-containing intermediate filaments found in the intracytoplasmic cytoskeleton of epithelial tissue. The term "cytokeratin" began to be used in the late 1970s when the protein subunits of keratin intermediate filaments inside cells were first being identified and...

 is not paired with a basic cytokeratin in epithelial cells. It is specifically found in the periderm, the transiently superficial layer that envelops the developing epidermis. The type I cytokeratins are clustered in a region of chromosome 17q12-q21.

Use as biomarker

Due to its high sensitivity, KRT19 is the most used marker for the RT-PCR
Reverse transcription polymerase chain reaction
Reverse transcription polymerase chain reaction is a variant of polymerase chain reaction , a laboratory technique commonly used in molecular biology to generate many copies of a DNA sequence, a process termed "amplification"...

-mediated detection of tumor cells disseminated in lymph node
Lymph node
A lymph node is a small ball or an oval-shaped organ of the immune system, distributed widely throughout the body including the armpit and stomach/gut and linked by lymphatic vessels. Lymph nodes are garrisons of B, T, and other immune cells. Lymph nodes are found all through the body, and act as...

s, peripheral blood, and bone marrow
Bone marrow
Bone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg...

 of breast cancer
Breast cancer
Breast cancer is cancer originating from breast tissue, most commonly from the inner lining of milk ducts or the lobules that supply the ducts with milk. Cancers originating from ducts are known as ductal carcinomas; those originating from lobules are known as lobular carcinomas...

 patients. Depending on the assays, KRT19 has been shown to be both a specific and a non-specific marker. False positivity in such KRT19 RT-PCR studies include: illegitimate transcription (expression of small amounts of KRT19 mRNA by tissues in which it has no real physiological role), haematological disorders (KRT19 induction in peripheral blood cells by cytokine
Cytokines are small cell-signaling protein molecules that are secreted by the glial cells of the nervous system and by numerous cells of the immune system and are a category of signaling molecules used extensively in intercellular communication...

s and growth factor
Growth factor
A growth factor is a naturally occurring substance capable of stimulating cellular growth, proliferation and cellular differentiation. Usually it is a protein or a steroid hormone. Growth factors are important for regulating a variety of cellular processes....

s, which circulate at higher concentrations in inflammatory conditions and neutropenia), the presence of pseudogene
Pseudogenes are dysfunctional relatives of known genes that have lost their protein-coding ability or are otherwise no longer expressed in the cell...

s (two KRT19 pseudogenes, KRT19a and KRT19b, have been identified, which have significant sequence homology to KRT19 mRNA. Subsequently, attempts to detect the expression of the authentic KRT19 may result in the detection of either or both of these pseudogenes), sample contamination (introduction of contaminating epithelial cells during peripheral blood sampling for subsequent RT-PCR analysis).

Keratin 19 is often used together with keratin 8
Keratin 8
Keratin, type I cytoskeletal 8 also known as cytokeratin-8 or keratin-8 is a keratin protein that in human is encoded by the KRT8 gene. It is often paired with keratin 18.-Utility as an immunohistochemical stain:...

 and keratin 18
Keratin 18
Keratin 18 is a type I cytokeratin. It is, together with its filament partner keratin 8, perhaps the most commonly found products of the intermediate filament gene family. They are expressed in single layer epithelial tissues of the body. Mutations in this gene have been linked to cryptogenic...

 to differentiate cells of epithelial origin from hematopoietic cells in tests that enumerate circulating tumor cell
Circulating Tumor Cell
Circulating tumor cells are cells that have detached from a primary tumor and circulate in the bloodstream. CTCs may constitute seeds for subsequent growth of additional tumors in different tissues....

s in blood.


Keratin 19 has been shown to interact
Protein-protein interaction
Protein–protein interactions occur when two or more proteins bind together, often to carry out their biological function. Many of the most important molecular processes in the cell such as DNA replication are carried out by large molecular machines that are built from a large number of protein...

 with Pinin
Pinin is a protein that in humans is encoded by the PNN gene.-Interactions:Pinin has been shown to interact with Keratin 8, Keratin 18, Keratin 19, CTBP1, RNPS1, PRPF4B, SFRS4, PPIG, SRRM2 and SFRS18.-Further reading:...


Further reading

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