Keratin 19

Keratin, type I cytoskeletal 19 (Keratin-19)) also known as cytokeratin-19 (CK-19) is a 40 kDa protein that in humans is encoded by the KRT19 gene.^[5][6] Keratin-19 is a type I keratin.

KRT19
Identifiers
Aliases	KRT19, CK19, K19, K1CS, keratin 19
External IDs	OMIM: 148020; MGI: 96693; HomoloGene: 1713; GeneCards: KRT19; OMA:KRT19 - orthologs
Gene location (Human) Chr. Chromosome 17 (human)[1] Band 17q21.2 Start 41,523,617 bp[1] End 41,528,308 bp[1]
Gene location (Mouse) Chr. Chromosome 11 (mouse)[2] Band 11 D|11 63.42 cM Start 100,031,636 bp[2] End 100,039,491 bp[2]
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in palpebral conjunctiva mucosa of transverse colon nasal epithelium mucosa of sigmoid colon olfactory zone of nasal mucosa amniotic fluid epithelium of nasopharynx epithelium of bronchus gallbladder bronchial epithelial cell Top expressed in epithelium of stomach crypt of lieberkuhn of small intestine mucous cell of stomach transitional epithelium of urinary bladder pyloric antrum left colon duodenum conjunctival fornix ileum lactiferous gland More reference expression data BioGPS More reference expression data
Gene ontology Molecular function protein-containing complex binding structural constituent of muscle structural constituent of cytoskeleton protein binding structural molecule activity Cellular component terminal web plasma membrane sarcolemma costamere dystrophin-associated glycoprotein complex Z discdkac extracellular exosome intermediate filament cell periphery cytosol apicolateral plasma membrane Biological process Notch signaling pathway viral process sarcomere organization cell differentiation involved in embryonic placenta development response to estrogen keratinization cornification Sources:Amigo / QuickGO
Orthologs Species Human Mouse Entrez 3880 16669 Ensembl ENSG00000171345 ENSMUSG00000020911 UniProt P08727 P19001 RefSeq (mRNA) NM_002276 NM_008471 NM_001313963 RefSeq (protein) NP_002267 NP_001300892 NP_032497 Location (UCSC) Chr 17: 41.52 – 41.53 Mb Chr 11: 100.03 – 100.04 Mb PubMed search [3] [4]
Wikidata
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Function

Keratin-19 is a member of the keratin 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 is not paired with a basic cytokeratin in epithelial cells. It is specifically found in the embryonic periderm, the transiently superficial layer that envelops the developing epidermis. The type I cytokeratins are clustered in a region of chromosome 17 (q12-q21).^[6]

Use as biomarker

CYFRA 21-1, a soluble fragment of KRT19, is a tumor marker of various types of cancer, including lung, breast, stomach, pancreas, ovary. KRT19 is commonly expressed in carcinomas of these organs and CYFRA 21-1 is produced when KRT19 is cleaved during cell apoptosis.^[7][8]

Due to its high sensitivity, KRT19 is the most used marker for the RT-PCR-mediated detection of tumor cells disseminated in lymph nodes, peripheral blood, and bone marrow of breast cancer patients. Depending on the assays, KRT19 has been shown to be both a specific and a non-specific marker.

False positivity in CYFRA 21-1 / 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 cytokines and growth factors, which circulate at higher concentrations in inflammatory conditions and neutropenia)
• the presence of pseudogenes (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).^[9]
• trauma and stress (such as shear stress, heat shock, toxins, infection, aging and oxidative stress such as from smoking), which increase KRT19 expression and cell apoptosis^[7]
• weight loss and muscle wasting/apoptosis (KRT19 is expressed in muscle)^[7]

Moreover, Ck-19 is widely applied as post-operative diagnostic marker of papillary thyroid carcinoma.^[10]

Keratin-19 is often used together with keratin 8 and keratin 18 to differentiate cells of epithelial origin from hematopoietic cells in tests that enumerate circulating tumor cells in blood.^[11]

Interactions

Keratin-19 has been shown to interact with Pinin.^[12]