INDUCIBLE EXPRESSION OF BCL-2 BY THE LAC OPERATOR REPRESSOR SYSTEM INMDCK CELLS/

The lac operator/repressor-inducible system was utilized to dissect th e biological consequences of human bcl-2 gene expression in Madin-Darb y canine kidney (MDCK) cells. Cells were made transgenic for a constit utively expressed lad gene, encoding lac repressor, and the bcl-2 gene that had been inserted downstream of a simian virus 40 (SV40) promote r containing the lac operator sequence. The expression of the bcl-2 ge ne could therefore be repressed to basal level by binding of lac repre ssor to the lac operator sequence in proximity to this SV40 regulatory region and be specifically activated by administration of the lactose analog isopropyl-beta-thiogalactoside (IPTG). We showed that expressi on of bcl-2 gene could be induced by 0.01 mM IPTG, and the maximal ind uction was obtained at 1 mM. With the treatment of IPTG, the Bcl-2 pro tein could be induced within 6 h. Moreover, the IPTG-inducible express ion of Bcl-2 protein is a reversible process. Finally, functional assa ys revealed that IPTG-induced expression of bcl-2 gene conferred parti al or complete resistance to homeless cell death or confluent cell dea th, respectively. The inducible expression system should be particular ly useful for dissecting the effect of bcl-2 in phenotypic or morpholo gical changes of MDCK cells.