sialomucin

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/11/05 10:31:43」(JST)

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Micrograph showing cells with prominent mucin-containing intracytoplasmic vacuoles. Pap stain.

Mucins are a family of high molecular weight, heavily glycosylated proteins (glycoconjugates) produced by epithelial tissues in most metazoans. Mucins' key characteristic is their ability to form gels; therefore they are a key component in most gel-like secretions, serving functions from lubrication to cell signalling to forming chemical barriers. They often take an inhibitory role. Some mucins are associated with controlling mineralization, including nacre formation in molluscs, calcification in echinoderms and bone formation in vertebrates. They bind to pathogens as part of the immune system. Overexpression of the mucin proteins, especially MUC1 is associated with many types of cancer.

Although some mucins are membrane-bound due to the presence of a hydrophobic membrane-spanning domain that favors retention in the plasma membrane, most mucins are secreted onto mucosal surfaces or secreted to become a component of saliva.

Genes

At least 19 human mucin genes have been distinguished by cDNA cloning — MUC1, MUC2, MUC3A, MUC3B, MUC4, MUC5AC, MUC5B, MUC6, MUC7, MUC8, MUC12, MUC13, MUC15, MUC16, MUC17, MUC19, and MUC20.

The major secreted airway mucins are MUC5AC and MUC5B, while MUC2 is secreted mostly in the intestine but also in the airway.

Protein structure

Mature mucins are composed of two distinct regions:

• The amino- and carboxy-terminal regions are very lightly glycosylated, but rich in cysteines. The cysteine residues participate in establishing disulfide linkages within and among mucin monomers.

• A large central region formed of multiple tandem repeats of 10 to 80 residue sequences in which up to half of the amino acids are serine or threonine. This area becomes saturated with hundreds of O-linked oligosaccharides. N-linked oligosaccharides are also found on mucins, but in less abundance than O-linked sugars.

Glycosylation and aggregation

Mucin genes encode mucin monomers that are synthesized as rod-shape apomucin cores that are post-translationally modified by exceptionally abundant glycosylation.

The dense "sugar coating" of mucins gives them considerable water-holding capacity and also makes them resistant to proteolysis, which may be important in maintaining mucosal barriers.

Mucins are secreted as massive aggregates of proteins with molecular masses of roughly 1 to 10 million Da. Within these aggregates, monomers are linked to one another mostly by non-covalent interactions, although intermolecular disulfide bonds may also play a role in this process.

Secretion

Upon stimulation, MARCKS (myristylated alanine-rich C kinase substrate) protein coordinates the secretion of mucin from mucin filled vesicles within the specialized epithelial cells. Fusion of the vesicles to the plasma membrane causes release of the mucin, which as it exchanges Ca²⁺ for Na⁺ expands up to 600 fold. The result is a viscoelastic product of interwoven molecules which, combined with other secretions (e.g., from the airway epithelium and the submucosal glands in the respiratory system), is called mucus.

Clinical significance

Increased mucin production occurs in many adenocarcinomas, including cancers of the pancreas, lung, breast, ovary, colon and other tissues. Mucins are also overexpressed in lung diseases such as asthma, bronchitis, COPD or cystic fibrosis. Two membrane mucins, MUC1 and MUC4 have been extensively studied in relation to their pathological implication in the disease process. Mucins are under investigation as possible diagnostic markers for malignancies and other disease processes in which they are most commonly over- or mis-expressed.

Abnormal deposits of mucin are responsible for the non-pitting facial edema seen in untreated hypothryoidism. This edema is seen in the pretibial area as well.

References

• Ali M, Hutton D, Wilson J, Pearson J (September 2005). "Major Secretory Mucin Expression in Chronic Sinusitis". Otolaryngology - Head and Neck Surgery 133 (3): 423–428. doi:10.1016/j.otohns.2005.06.005. PMID 16143194. 

External links

• Mucins at the US National Library of Medicine Medical Subject Headings (MeSH)
• "Mucin" at Dorland's Medical Dictionary

UpToDate Contents

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• Kim S1, Guo J2,3, O'Sullivan MG3,4, Gallaher DD1, Turesky RJ2,3.
• Environmental and molecular mutagenesis.Environ Mol Mutagen.2016 Mar;57(2):125-36. doi: 10.1002/em.21993. Epub 2016 Jan 6.
• Considerable evidence suggests that environmental factors, including diet and cigarette smoke, are involved in the pathogenesis of colon cancer. Carcinogenic nitroso compounds (NOC), such as N-nitrosodimethylamine (NDMA), are present in tobacco and processed red meat, and NOC have been implicated in
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• The cell surface mucin podocalyxin regulates collective breast tumor budding.

• Graves ML1, Cipollone JA2, Austin P3, Bell EM4, Nielsen JS5, Gilks CB6, McNagny KM7, Roskelley CD8.
• Breast cancer research : BCR.Breast Cancer Res.2016 Jan 22;18(1):11. doi: 10.1186/s13058-015-0670-4.
• BACKGROUND: Overexpression of the transmembrane sialomucin podocalyxin, which is known to play a role in lumen formation during polarized epithelial morphogenesis, is an independent indicator of poor prognosis in a number of epithelial cancers, including those that arise in the breast. Therefore, we
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• Podocalyxin-like protein 1 functions as an immunomodulatory molecule in breast cancer cells.

• Amo L1, Tamayo-Orbegozo E1, Maruri N1, Buqué A2, Solaun M3, Riñón M1, Arrieta A1, Larrucea S4.
• Cancer letters.Cancer Lett.2015 Nov 1;368(1):26-35. doi: 10.1016/j.canlet.2015.06.029. Epub 2015 Aug 11.
• Podocalyxin-like protein 1 (PCLP1), a CD34-related sialomucin involved in the regulation of cellular morphology and adhesion, is expressed by a number of normal cells and various tumor cells. In breast malignancies PCLP1 overexpression has been associated with the most aggressive, metastatic cancers
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Japanese Journal

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• ウイルス 62(1), 121-128, 2012-06-01
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• Podoplanin promotes cell migration via the EGF-Src-Cas pathway in oral squamous cell carcinoma cell lines

• Journal of Oral Science 54(3), 241-250, 2012
• NAID 130002070047

• Immunohistochemical expression of podoplanin in so-called hard α-keratin-expressing tumors, including calcifying cystic odontogenic tumor, craniopharyngioma, and pilomatrixoma

• Journal of Oral Science 54(2), 165-175, 2012
• NAID 130002070030

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