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

Oncogene. 1997 Oct 9;15(15):1859-70. doi: 10.1038/sj.onc.1201530.

Abstract

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.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Cell Differentiation / genetics*
  • Colforsin / pharmacology
  • Cyclic AMP / analogs & derivatives
  • Cyclic AMP / pharmacology*
  • Enhancer Elements, Genetic*
  • Genes, Reporter
  • Introns*
  • Leukemia, Erythroblastic, Acute / genetics*
  • Leukemia, Erythroblastic, Acute / metabolism
  • Leukemia, Erythroblastic, Acute / pathology
  • Mice
  • NF-kappa B / metabolism*
  • Oncogenes*
  • Protein Binding
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Subcellular Fractions / metabolism
  • Transcription Factors / metabolism
  • Tumor Cells, Cultured

Substances

  • NF-kappa B
  • RNA, Messenger
  • Transcription Factors
  • Colforsin
  • Cyclic AMP