Keratin 7 Explained

Keratin, type II cytoskeletal 7 also known as cytokeratin-7 (CK-7) or keratin-7 (K7) or sarcolectin (SCL) is a protein that in humans is encoded by the KRT7 gene.^{[1] [2] [3]} Keratin 7 is a type II keratin. It is specifically expressed in the simple epithelia lining the cavities of the internal organs and in the gland ducts and blood vessels.

Function

Keratin-7 is a member of the keratin gene family. The type II cytokeratins consist of basic or neutral proteins which are arranged in pairs of heterotypic keratin chains coexpressed during differentiation of simple and stratified epithelial tissues. This type II cytokeratin is specifically expressed in the simple epithelia lining the cavities of the internal organs and in the gland ducts and blood vessels. The genes encoding the type II cytokeratins are clustered in a region of chromosome 12q12-q13. Alternative splicing may result in several transcript variants; however, not all variants have been fully described.^[3]

Keratin-7 is found in simple glandular epithelia, and in transitional epithelium. Epithelial cells of the lung and breast both contain keratin-7, but some other glandular epithelia, such as those of the colon and prostate, do not.

Immunohistochemistry

Because the keratin-7 antigen is found in both healthy and neoplastic cells, antibodies to CK7 can be used in immunohistochemistry to distinguish ovarian and transitional cell carcinomas (staining positive) from colonic and prostate cancers (negative), respectively. It is commonly used together with CK20 when making such diagnoses.^[4]

Further reading

• Bouwens L . Cytokeratins and cell differentiation in the pancreas . The Journal of Pathology . 184 . 3 . 234–9 . Mar 1998 . 9614373 . 10.1002/(SICI)1096-9896(199803)184:3<234::AID-PATH28>3.0.CO;2-D . 19443756 .
• Glass C, Kim KH, Fuchs E . Sequence and expression of a human type II mesothelial keratin . The Journal of Cell Biology . 101 . 6 . 2366–73 . Dec 1985 . 2415537 . 2114014 . 10.1083/jcb.101.6.2366 .
• Ramaekers F, Huysmans A, Schaart G, Moesker O, Vooijs P . Tissue distribution of keratin 7 as monitored by a monoclonal antibody . Experimental Cell Research . 170 . 1 . 235–49 . May 1987 . 2436934 . 10.1016/0014-4827(87)90133-9 .
• Glass C, Fuchs E . Isolation, sequence, and differential expression of a human K7 gene in simple epithelial cells . The Journal of Cell Biology . 107 . 4 . 1337–50 . Oct 1988 . 2459129 . 2115265 . 10.1083/jcb.107.4.1337 .
• Maruyama K, Sugano S . Oligo-capping: a simple method to replace the cap structure of eukaryotic mRNAs with oligoribonucleotides . Gene . 138 . 1–2 . 171–4 . Jan 1994 . 8125298 . 10.1016/0378-1119(94)90802-8 .
• Gress TM, Müller-Pillasch F, Geng M, Zimmerhackl F, Zehetner G, Friess H, Büchler M, Adler G, Lehrach H . A pancreatic cancer-specific expression profile . Oncogene . 13 . 8 . 1819–30 . Oct 1996 . 8895530 .
• Suzuki Y, Yoshitomo-Nakagawa K, Maruyama K, Suyama A, Sugano S . Construction and characterization of a full length-enriched and a 5'-end-enriched cDNA library . Gene . 200 . 1–2 . 149–56 . Oct 1997 . 9373149 . 10.1016/S0378-1119(97)00411-3 .
• Alvarez Alvarez C, Sánchez Merino JM, Busto Castañón L, Pombo Felipe F, Arnal Monreal F . [Mucinous adenocarcinoma of the urachus synchronic with colorectal adenocarcinoma. Value of immunohistochemistry in the differential diagnosis] . Actas Urologicas Españolas . 22 . 6 . 515–8 . Jun 1998 . 9734130 .
• Kaba A, Jiang PH, Chany-Fournier F, Chany C . Sarcolectin (SCL): structure and expression of the recombinant molecule . Biochimie . 81 . 7 . 709–15 . Jul 1999 . 10492017 . 10.1016/S0300-9084(99)80128-X .
• Lin L, Holbro T, Alonso G, Gerosa D, Burger MM . Molecular interaction between human tumor marker protein p150, the largest subunit of eIF3, and intermediate filament protein K7 . Journal of Cellular Biochemistry . 80 . 4 . 483–90 . 2001 . 11169732 . 10.1002/1097-4644(20010315)80:4<483::AID-JCB1002>3.0.CO;2-B . 35848129 .
• Suzuki H, Fukunishi Y, Kagawa I, Saito R, Oda H, Endo T, Kondo S, Bono H, Okazaki Y, Hayashizaki Y . Protein-protein interaction panel using mouse full-length cDNAs . Genome Research . 11 . 10 . 1758–65 . Oct 2001 . 11591653 . 311163 . 10.1101/gr.180101 .
• Harris RA, Yang A, Stein RC, Lucy K, Brusten L, Herath A, Parekh R, Waterfield MD, O'Hare MJ, Neville MA, Page MJ, Zvelebil MJ . Cluster analysis of an extensive human breast cancer cell line protein expression map database . Proteomics . 2 . 2 . 212–23 . Feb 2002 . 11840567 . 10.1002/1615-9861(200202)2:2<212::AID-PROT212>3.0.CO;2-H . 44946014 .
• Bonvini P, Gastaldi T, Falini B, Rosolen A . Nucleophosmin-anaplastic lymphoma kinase (NPM-ALK), a novel Hsp90-client tyrosine kinase: down-regulation of NPM-ALK expression and tyrosine phosphorylation in ALK(+) CD30(+) lymphoma cells by the Hsp90 antagonist 17-allylamino,17-demethoxygeldanamycin . Cancer Research . 62 . 5 . 1559–66 . Mar 2002 . 11888936 .
• Jovanovic I, Tzardi M, Mouzas IA, Micev M, Pesko P, Milosavljevic T, Zois M, Sganzos M, Delides G, Kanavaros P . Changing pattern of cytokeratin 7 and 20 expression from normal epithelium to intestinal metaplasia of the gastric mucosa and gastroesophageal junction . Histology and Histopathology . 17 . 2 . 445–54 . Apr 2002 . 11962749 .
• Kanduc D . Translational regulation of human papillomavirus type 16 E7 mRNA by the peptide SEQIKA, shared by rabbit alpha(1)-globin and human cytokeratin 7 . Journal of Virology . 76 . 14 . 7040–8 . Jul 2002 . 12072504 . 136328 . 10.1128/JVI.76.14.7040-7048.2002 .
• Smith FJ, Porter RM, Corden LD, Lunny DP, Lane EB, McLean WH . Cloning of human, murine, and marsupial keratin 7 and a survey of K7 expression in the mouse . Biochemical and Biophysical Research Communications . 297 . 4 . 818–27 . Oct 2002 . 12359226 . 10.1016/S0006-291X(02)02288-X .
• Blagoev B, Kratchmarova I, Ong SE, Nielsen M, Foster LJ, Mann M . A proteomics strategy to elucidate functional protein-protein interactions applied to EGF signaling . Nature Biotechnology . 21 . 3 . 315–8 . Mar 2003 . 12577067 . 10.1038/nbt790 . 26838266 .

Notes and References

1. Rosenberg M, Fuchs E, Le Beau MM, Eddy RL, Shows TB . Three epidermal and one simple epithelial type II keratin genes map to human chromosome 12 . Cytogenetics and Cell Genetics . 57 . 1 . 33–8 . Aug 1991 . 1713141 . 10.1159/000133109 .
2. Schweizer J, Bowden PE, Coulombe PA, Langbein L, Lane EB, Magin TM, Maltais L, Omary MB, Parry DA, Rogers MA, Wright MW . New consensus nomenclature for mammalian keratins . The Journal of Cell Biology . 174 . 2 . 169–74 . Jul 2006 . 16831889 . 2064177 . 10.1083/jcb.200603161 .
3. Web site: Entrez Gene: KRT7 keratin 7.
4. Book: Leong, Anthony S-Y. Cooper, Kumarason. Leong, F Joel W-M. 2003. Manual of Diagnostic Cytology. 2. Greenwich Medical Media, Ltd.. 173. 978-1-84110-100-2.