Mediator caused induction of a human bradykinin B1 receptor minigene: Participation of c-Jun in the process

The bradykinin B1 receptor (BKB1R) gene is expressed in selected tissues su ch as lung and kidney. In these tissues it is expressed at a very low level until induced by inflammatory mediators. Our aim has been to understand th e mechanism of th is regulatory process. A human BKB1R minigene was constru cted. It contained a 1.8 kb promoter, the entire exon 1, 1.5 kb of intron I , the entire exon II and intron II, and the luciferase gene as a reporter. Transient transfection of the minigene into SV40-transformed IMR90 cells (I MRSV) resulted in a promoter activity which was activated by the mediators, lipopolysaccharide (FPS) and desArg(10)-kallidin. In contrast, these media tors did not induce the activity of the 1.8 kb promoter construct alone. Th us, motifs exclusive of the promoter such as 5'-UTR and/or intron regions a re required for mediator-induced expression of this gene. Promoter activiti es of both the minigene and the 1.8 kb promoter construct were enhanced in a dose-dependent manner upon cotransfection with c-Jun. Furthermore, cotran sfecting c-Jun with the minigene achieved the maximal promoter activity wit h no further increase in response to mediators. Conversely, the induction o f the minigene promoter activity by mediators was abolished upon cotransfec tion with a dominant negative mutant of c-Jun. Other experiments suggest th at multiple AP-1 sites are interactive with the c-Jun upregulation of this gene. Taken together, these results point to c-jun as a key intermediary in the activation of the expression of this gene by mediators. However, parti cipation of motifs outside of the promoter are necessary to obtain this ind ucible expression.