The reference OMIM entry for this protein is 148059

Keratin 7, type ii; krt7
K7
Kb7
Keratin, simple epithelial
Keratin, type ii, cytoskeletal, 7; k2c7
Sarcolectin; scl

DESCRIPTION

Keratins are proteins that compose the 8-nm intermediate filaments in epithelial cells. KRT7 is a type II keratin of simple nonkeratinizing epithelia (Glass et al., 1985).

CLONING

By cross-hybridization with a K6A (148041) cDNA probe, Glass et al. (1985) cloned KRT7, which they designated K7, from a mesothelial cell cDNA library. The deduced 489-amino acid protein has a calculated molecular mass of about 54 kD. K7 contains 4 central alpha-helical segments with heptad repeats of hydrophobic residues characteristic of a coiled-coil region. Within this domain, K7 shares 73% homology with epidermal K6B (148042). The nonhelical N and C termini of K7 are substantially different in sequence and size from those of K6B and other epidermal type II keratins. K7 has an isoelectric point of 5.8, which is more acidic than those of other type II keratins. Northern blot analysis detected a 1.7-kb transcript in epidermis, bronchus, and mesothelium, but not in colon, exocervix, or liver. By screening a genomic library using probes to the 5-prime and 3-prime K7 cDNA reported by Glass et al. (1985), Glass and Fuchs (1988) isolated overlapping genomic clones for K7. They identified a 1-bp insertion in the K7 coding sequence that was inadvertently omitted by Glass et al. (1985). The change results in a deduced 468-amino acid K7 protein with a different N terminus than that reported by Glass et al. (1985). Smith et al. (2002) cloned K7 from human, mouse, and rat kangaroo libraries. The deduced human K7 protein contains 469 amino acids and has a calculated molecular mass of 51.4 kD. K7 shares 82% amino acid identity with mouse K7 and 76% identity with rat kangaroo K7. Western blot analysis of mouse tissues detected K7 expression in bladder, but not in epidermis. Smith et al. (2002) found K7 expression restricted to ducts and specific glands of simple epithelial tissues; examples included isolated cells in the acini of mammary gland, cells of lung alveoli and bronchiolar epithelium, kidney collecting duct, and Brunner glands of the duodenum.

GENE FUNCTION

Glass and Fuchs (1988) determined that expression of endogenous K7 in rat kangaroo kidney cells was upregulated by retinoic acid, although retinoic acid did not affect basal K7 expression.

GENE STRUCTURE

Glass and Fuchs (1988) determined that the KRT7 gene contains 8 exons. The 5-prime upstream region contains a TATA-like sequence and a CCAAT sequence. The promoter region contains binding sites for SP1 (189906), AP1 (see 165160), and FOS (164810). Smith et al. (2002) determined that the KRT7 gene contains 9 exons and spans more than 15.6 kb. They identified 4 CpG islands conserved in the human, mouse, and rat kangaroo KRT7 genes. The first island is located upstream of exon 1, the second is within exon 1, the third, a short island, is located toward the end of intron 4, and the fourth is downstream of exon 9.

MAPPING

By Southern blot analysis, Glass et al. (1985) determined that KRT7 is a single copy gene; however, Glass and Fuchs (1988) presented evidence that there may be other copies. Rosenberg et al. (1991) assigned the K7 gene to chromosome 12 using Southern blot analysis of somatic cell hybrids. They sublocalized the gene to chromosome 12q12-q14 by in situ hybridization of metaphase chromosomes. By genomic sequence analysis, Smith et al. (2002) determined that the human and mouse KRT7 genes map to the periphery of the type II keratin gene ... More on the omim web site

Subscribe to this protein entry history

Oct. 20, 2018: Protein entry updated
Automatic update: OMIM entry 148059 was added.

Oct. 19, 2018: Additional information
Initial protein addition to the database. This entry was referenced in Bryk and co-workers. (2017).