Bcl-3 Expression and Nuclear Translocation Are Induced by Granulocyte-Macrophage Colony-Stimulating Factor and Erythropoietin in Proliferating Human Erythroid Precursors

Abstract

AbstractBcl-3 is a proto-oncogene involved in the chromosomal translocation t(14;19) found in some patients with chronic lymphocytic leukemia. It shares structural similarities with and is a member of the IκB family of proteins. In this report, involvement of Bcl-3in hematopoietic growth factor-stimulated erythroid proliferation and differentiation was examined. In TF-1 cells, an erythroleukemia cell line, granulocyte-macrophage colony-stimulating factor (GM-CSF) and erythropoietin (Epo) greatly enhanced Bcl-3 expression at both the protein and mRNA levels in association with stimulation of proliferation. Bcl-3 protein was also highly expressed in early burst-forming unit-erythroid (BFU-E)–derived erythroid precursors (day 7) and decreased during maturation (days 10 and 14), suggesting that Bcl-3 is involved in normal erythroid proliferation. In these hematopoietic cells, Bcl-3 was hyperphosphorylated. GM-CSF and Epo modulated the subcellular localization of Bcl-3. Upon stimulation of TF-1 cells with GM-CSF or Epo, the nuclear translocation ofBcl-3 was dramatically enhanced. Overexpression of Bcl-3 in TF-1 cells by transient transfection along with the NF-κB factors p50 or p52 resulted in significant induction of an human immunodeficiency virus–type 1 (HIV-1) κB-TATA-luceriferase reporter plasmid, demonstrating that Bcl-3 has a positive role in transactivation of κB-containing genes in erythroid cells. Stimulation with GM-CSF enhanced c-myb mRNA expression in these cells. Bcl-3 in nuclear extracts of TF-1 cells bound to a κB enhancer in the c-mybpromoter together with NF-κB2/p52 and this binding activity was enhanced by GM-CSF stimulation. Furthermore, cotransfection of Bcl-3 with p52 or p50 in TF-1 cells resulted in significant activation of ac-myb κB-TATA-luceriferase reporter plasmid. These findings suggest that Bcl-3 may participate in the transcriptional regulation of certain κB-containing genes involved in hematopoiesis, includingc-myb.© 1998 by The American Society of Hematology.