Simple epithelial keratins

Squamous cell carcinomas of different sites of origin are generally characterized by a predominance of stratified-epithelial/keratinocyte-type keratins but may coexpress certain simple-epithelial keratins (for details, see Moll 1998). Most of these... 

Owens DW, Lane EB (2003) The quest for the function of simple epithelial keratins. Bioessays 25(8) 748 758... 

The role of the IF, and particularly the keratin filament system, in resisting the forces of mechanical stress has been well established. However, IFs also play a role in countering metabolic stress. Perhaps the best example is the cytoprotective role played by the simple epithelial keratins, K8/18. However, vimentin, desmin, peripherin, GFAP, the lens proteins phakinin, and filensin and other keratins have also been shown to associate with members of the small heat shock protein (HSP) family, including HSP27 and aB-crystallin (reviewed in Coulombe and Wong, 2004 Marceau et al., 2001 Nicholl and Quinlan, 1994). 

Liao,J., and Omary, M. B. (1996). 14-3-3 proteins associate with phosphorylated simple epithelial keratins during cell cycle progression and act as a solubility cofactor. / Cell. Biol. 133, 345-357. 

Simple epithelial keratins are the first keratins to appear in embryonic development because they are expressed in virtually all simple (nonstratified), ductal, and pseudo-stratified epithelial tissuesd° >ii° Because these keratins... 

Gilbert, S., Loranger, A., and Marceau, N. (2004). Keratins modulate c-Flip/extracellu-lar signal-regulated kinase 1 and 2 antiapoptotic signaling in simple epithelial cells. Mol. Cell. Biol. 24, 7072-7081. 

Marceau, N., Loranger, A., Gilbert, S., Daigle, N., and Champetier, S. (2001). Keratin-mediated resistance to stress and apoptosis in simple epithelial cells in relation to health and disease. Biochem. Cell Biol. 79, 543-555. 

Rosenberg M, Fuchs E, Le Beau MM, et al. Three epidermal and one simple epithelial type II keratin genes map to human chromosome 12. Cytogenet Cell Genet. 1991 57 33-38. 

Albers K, Fuchs E (1987) The expression of mutant epidermal keratin cDNAs transfected in simple epithelial and squamous cell carcinoma lines. J Cell Biol 105(2) 791-806... 

A single layer of epithelial cells is termed simple epithelium, whereas those composed of more than one layer are termed stratified epithelia. Stratified epithelia are found in areas which have to withstand large amounts of wear and tear, for example the inside of the mouth, orthe skin. Epithelial cells may be, for example, squamous (flattened), columnar (tall), cuboidal (intermediate between squamous and columnar) and may contain surface specializations, such as cilia in the nasal epithelium and keratin in the skin. 

Epithelial cells contain keratins cytosolic, intermediate-sized filaments. Each acidic keratin (type I) is partnered with a basic keratin (type II) to form extended, intertwined alpha helices. These heterodimers extend longitudinally and laterally in staggered and/ or end-to-end arrays to form cytosolic intermediate filaments. Different keratin types account for the properties of different types of epithelia. A stratified epithelium provides a barrier consisting of multiple layers of cells in which the basal layer expresses K5-K14 but the supra-basal layers express K1-K10. Junctional epithelium has inner and outer basal layers that contain K5-K14. Its supra-basal layers possess K4 and K13, not K1 and K10 and it therefore has no granular layer. Desmosomes permit water and metabolite exchange beneath the granular layer, but they are mostly absent from junctional epithelium which is fluid-permeable like a simple epithelium. The cells of both basal layers of junctional epithelium proliferate and shed their progeny into the base of the sulcus. Junctional epithelium also secretes and activates TGF-pi, which prevents an inflammatory response to masticatory trauma. 

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