Integration of tetracycline regulation into a cell-specific transcriptional enhancer

The pancreas-specific transcriptional enhancer of the rat elastase I gene was modified by substituting, in turn, each of its three individual constitutive elements with the tetO element, which confers regulation by exogenous tetracycline in the presence of the hybrid tetO binding transactivator (tTA). Whereas the unmodified enhancer was active in transfected acinar tumor cells, substitution of individual elements with the tet-responsive element abolished activity. The modified enhancers were reactivated in the presence of the tTA and, upon addition of tetracycline, were silenced. Thus, substitution of individual enhancer elements renders the enhancer responsive to regulation by tetracycline. Moreover, the tTA-activated levels were 2-8-fold greater than the unmodified enhancer. The acinar cell specificity of the unmodified enhancer was retained; none of the tetO-substituted enhancers were activated by tTA in a variety of nonacinar cell lines. These results show that a foreign and artificial transcriptional activator, tTA, can be incorporated into an enhancer to create a novel, efficient, and regulatable transcriptional control region whose cell specificity is retained.