Onset of re-epithelialization after skin injury correlates with a reorganization of keratin filaments in wound edge keratinocytes: defining a potential role for keratin 16

Injury to stratified epithelia causes a strong induction of keratins 6 (K6) and 16 (K16) in post-mitotic keratinocytes located at the wound edge. We show that induction of K6 and K16 occurs within 6 h after injury to human epidermis. Their subsequent accumulation in keratinocytes correlates with the profound reorganization of keratin filaments from a pan-cytoplasmic distribution to one in which filaments are aggregated in a juxtanuclear location, opposite to the direction of cell migration. This filament reorganization coincides with additional cytoarchitectural changes and the onset of re-epithelialization after 18 h post-injury. By following the assembly of K6 and K16 in vitro and in cultured cells, we find that relative to K5 and K14, a well- characterized keratin pair that is constitutively expressed in epidermis, K6 and K16 polymerize into short 10-nm filaments that accumulate near the nucleus, a property arising from K16. Forced expression of human K16 in skin keratinocytes of transgenic mice causes a retraction of keratin filaments from the cell periphery, often in a polarized fashion. These results imply that K16 may not have a primary structural function akin to epidermal keratins. Rather, they suggest that in the context of epidermal wound healing, the function of K16 could be to promote a reorganization of the cytoplasmic array of keratin filaments, an event that precedes the onset of keratinocyte migration into the wound site.