cAMP-induced NF-kappaB (p50/relB) binding to a c-myb intronic enhancer correlates with c-myb up-regulation and inhibition of erythroleukemia cell differentiation.
During hexamethylene bisactamide (HMBA)-induced differentiation of murine erythroleukemia (MEL) cells erythroid genes are transcriptionally activated while c-myb and several other nuclear proto-oncogenes are down-regulated. Differentiation is inhibited by cAMP analogues and the adenyl cyclase-stimulating agent forskolin. We found that these drugs prevented the late down-regulation of c-myb which is known to be critical for MEL cell differentiation. Since the increase in c-myb mRNA levels was due to increased mRNA transcription, we examined the transcription factors NF-kappaB and AP-1 which have been implicated in the regulation of c-myb expression. Binding of MEL cell nuclear proteins to a NF-kappaB recognition sequence in c-myb intron I was strongly induced by 8-Br-cAMP or forskolin; induction was delayed and correlated with the up-regulation of c-myb. The cAMP-induced NF-kappaB complex contained p50 and RelB; in co-transfection assays, p50 and RelB transactivated a reporter construct containing the c-myb intronic NF-kappaB site upstream of a minimal promoter. 8-Br-cAMP and forskolin also increased the DNA binding activity of AP-1 complexes containing JunB, JunD and c-Fos in MEL cells which could cooperate with NF-kappaB. We conclude that inhibition of MEL cell differentiation by pharmacological doses of cAMP can be explained by the up-regulation of c-myb which is mediated, at least in part, by NF-kappaB p50/RelB heterodimers.
Suhasini
M
M
Department of Medicine and Cancer Centre, University of California, San Diego, La Jolla 92093, USA.
Reddy
C D
CD
Reddy
E P
EP
DiDonato
J A
JA
Pilz
R B
RB
D000818:Animals; D002454:Cell Differentiation / Q000235:genetics*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology*; D004742:Enhancer Elements, Genetic; D017930:Genes, Reporter; D007438:Introns; D004915:Leukemia, Erythroblastic, Acute / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D051379:Mice; D016328:NF-kappa B / Q000378:metabolism*; D009857:Oncogenes; D011485:Protein Binding; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013347:Subcellular Fractions / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D014407:Tumor Cells, Cultured
D016328:NF-kappa B; D012333:RNA, Messenger; D014157:Transcription Factors; D005576:Colforsin; D000242:Cyclic AMP