Defining a region of the human keratin 6a gene that confers inducible expression in stratified epithelia of transgenic mice.

Injury to the epidermis and other stratified epithelia triggers a repair response involving the rapid induction of several genes, including keratin 6 (K6). The signaling pathways and mechanisms presiding over this induction in keratinocytes at the wound edge remain to be defined. We reported previously that of the multiple genes encoding K6 isoforms in human, K6a is dominant in skin epithelia (Takahashi, K., Paladini, R., Coulombe, P. A. (1995) J. Biol. Chem. 270, 18581-18592). Using bacterial LacZ as a reporter gene in transgenic mice, we show that the proximal 5.2 kilobases of 5'-upstream sequence from the K6a gene fails to direct sustained expression in any adult tissue, including those where K6 is constitutively expressed (e.g. hair follicle, nail, oral mucosa, tongue, esophagus, forestomach). In contrast, the proximal 960 base pairs of 5'-upstream sequence suffice to mediate an induction of beta-galactosidase expression in a near-correct spatial and temporal fashion after injury to epidermis and other stratified epithelia. Transgene expression also occurs following topical application of phorbol esters, all-trans-retinoic acid, or 2-4-dinitro-1-fluorobenzene, all known to induce K6 expression in skin. Our data show that critical regulatory sequences for this inducibility are located between -960 and -550 bp in the 5'-upstream sequence of K6a and that their activity is influenced by enhancer element(s) located between -2500 and -5200 base pairs. These findings have important implications for the control of gene expression after injury to stratified epithelia.