Type I keratin 16 forms relatively unstable tetrameric assembly subunits with various type II keratin partners: biochemical basis and functional implications.

Abstract

Type II keratin 6 (K6) and type I keratins 16 and 17 (K16 and K17) are intermediate-filament (IF) proteins that are induced in wound-edge keratinocytes as early as 4-6 h after injury to skin, either human or mouse. This induction occurs at the expense of the keratin proteins that are normally expressed in differentiating epidermal keratinocytes. Correlated with these changes in protein expression, keratinocytes-for 24 h following injuryundergo major cytoarchitectural alterations that affect their shape, intracellular organization, surface morphology, and adhesion properties. We recently proposed that the intrinsic properties of K16 are compatible with a direct role in keratinocyte activation at the wound edge (Paladini et al., 1996). Unlike K14, a related type I keratin that is constitutively expressed in epidermis, we found that K16 forms unstable heterotetramer subunits that polymerize into shorter filaments when paired with a variety of type II keratin partners (e.g., K5, K6b, K8). Such properties are of particular interest because it has been shown in a number of studies that the tetramer subunit predominates in the soluble pool of IF subunits in epithelial and nonepithelial cell lines in culture. The tetramer-forming properties of K16 may thus influence its dynamic parti-