ANALYSIS OF SEQUENCES CONTROLLING TISSUE-SPECIFIC AND HYPERPROLIFERATION-RELATED KERATIN-6 GENE-EXPRESSION IN TRANSGENIC MICE

Keratin 6 (K6) is an intermediate filament protein found in hair folli cles and in several internal stratified epithelia. This keratin has be en the focus of special attention because it is also strongly induced in epidermal interfollicular keratinocytes in hyperproliferative situa tions and in certain conditions leading to abnormal differentiation, T o localize and identify the sequences controlling this complex express ion pattern, and because of their potential use in transgenic mouse mo dels and gene therapy strategies for epidermal hyperproliferative diso rders, we have thoroughly analyzed a 9 kbp region of this gene previou sly shown to direct proper tissue-specific and inducible expression in transgenic mice, To reproduce the K6 constitutive expression pattern, cooperation is necessary between elements located in at least two dif ferent regions, one distal between -9 and -4 kbp and one proximal betw een -830 and -125 bp with respect to the CAP site. The ability to indu ce expression under hyperproliferative conditions resides in the 2.4 k bp fragment preceding the transcription start site, When this DNA frag ment was analyzed in more detail, we found that all subfragments teste d contained regulatory elements necessary for inducible expression, Th us, a complex organization of K6 regulatory elements emerges, as both the constitutive and the inducible expressions of this gene are under the control of multiple elements dispersed throughout relatively large 5' flanking DNA fragments, These findings will allow the expression o f cloned genes in transgenic mouse skin in response to pathological or applied hyperproliferative stimuli, avoiding the effects of their con stitutive expression in other epithelia.