CAMP-INDUCED NF-KAPPA-B (P50 RELB) BINDING TO A C-MYB INTRONIC ENHANCER CORRELATES WITH C-MYB UP-REGULATION AND INHIBITION OF ERYTHROLEUKEMIA CELL-DIFFERENTIATION/
M. Suhasini et al., CAMP-INDUCED NF-KAPPA-B (P50 RELB) BINDING TO A C-MYB INTRONIC ENHANCER CORRELATES WITH C-MYB UP-REGULATION AND INHIBITION OF ERYTHROLEUKEMIA CELL-DIFFERENTIATION/, Oncogene, 15(15), 1997, pp. 1859-1870
During hexamethylene bisactamide (HMBA)-induced differentiation of mur
ine erythroleukemia (MEL) cells erythroid genes are transcriptionally
activated while c-myb and several other nuclear proto-oncogenes are do
wn-regulated. Differentiation is inhibited by cAMP analogues and the a
denyl cyclase-stimulating agent forskolin. We found that these drugs p
revented the late down-regulation of c-myb which is known to be critic
al for MEL cell differentiation. Since the increase in c-myb mRNA leve
ls was due to increased mRNA transcription, we examined the transcript
ion factors NF-kappa B and AP-1 which have been implicated in the regu
lation of c-myb expression. Binding of MEL cell nuclear proteins to a
NF-kappa B recognition sequence in c-myb intron 1 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-kappa B complex contai
ned p50 and RelB; in co-transfection assays, p50 and RelB transactivat
ed a reporter construct containing the c-myb intronic NF-kappa B 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-kappa B. We conclude
that inhibition of MEL cell differentiation by pharmacological doses o
f cAMP can be explained by the up-regulation of c-myb which is mediate
d, at least in part, by NF-kappa B p50/RelB heterodimers.