NF-IL6, A MEMBER OF THE C EBP FAMILY OF TRANSCRIPTION FACTORS, BINDS AND TRANS-ACTIVATES THE HUMAN MDR1 GENE PROMOTER/

Revealing the regulatory mechanisms involved in P-glycoprotein express ion is important to our understanding of multidrug resistance (MDR) in tumor cells. The MDR1 gene encoding P-glycoprotein contained a promot er sequence (-157 to -125) that was found to be hemologous with other mdr gene promoters and that specifically interacted with a nuclear pro tein. The nuclear protein was identified, using a HeLa lambda gt11 cDN A expression library, to be the transcriptional regulator nuclear fact or for interleukin-6 (NF-IL6), a member of the C/EBP family of transcr iption factors that bound an NF-IL-6-like concensus element 5'-TTTCGCA GT-3'. Furthermore, a glutathione S-transferase fusion protein (10.1-g lutathione S-transferase) containing the partial NF-ILG cDNA was also found to specifically interact with the MDR1 promoter sequence. Co-tra nsfection of an NF-ILG expression vector with a chloramphenicol acetyl transferase reporter gene driven by 1018 base pairs of MDR1 5'-flankin g sequences demonstrated that NF-ILG transactivated the MDR1 promoter. This trans-activation was significantly reduced when the NF-IL6 eleme nt in the reporter gene construct was deleted or mutated. Identificati on of NF-ILG as an important transcriptional regulator and the implica tions of its potential role in MDR1 gene induction in response to a va riety of stimuli are discussed.