Differential expression of bcl-2 homologs in human CD34(+) hematopoietic progenitor cells induced to differentiate into erythroid or granulocytic cells.
The Bcl-2 family of proteins has been shown to play a central role in the regulation of apoptosis. We have examined the expression of several Bcl-2 homologs upon stimulation of CD34(+) human hematopoietic progenitor cells. CD34(+) cells were induced to differentiate into predominantly erythroid cells in the presence of erythropoietin (Epo) and stem cell factor (SCF), while the addition of G-CSF and SCF led to differentiation predominantly into granulocytic cells, as demonstrated by immunophenotyping and morphological examination of cultured cells. In Epo- and SCF-stimulated cells, we found a marked increase in the level of Bcl-x(L) protein expression and downregulation of Bax expression, apparent from day 4 and more pronounced on days 8 and 21. In contrast, Bcl-x(L) protein expression was downregulated in G-CSF- and SCF-stimulated cells compared with cells cultured in medium alone, whereas there was no sign of change in the level of Bax. Mcl-1 expression showed a biphasic expression pattern in both early erythropoiesis and early granulopoiesis, but with an inverse regulation. Thus, Mcl-1 levels initially decreased in granulocytic progenitor cells and increased in erythroid progenitor cells. Finally, Bcl-2 expression was significantly downregulated in both Epo and SCF and G-CSF- and SCF-stimulated cells. The role of the distinct upregulation of Bcl-x(L) in early erythroid differentiation was further examined by use of specific ribozymes against Bcl-x(L). Addition of Bcl-x(L) ribozymes promoted a clear increase in cell death of Epo- and SCF-stimulated cells, while erythroid differentiation was not affected. In conclusion, we found a distinct regulation of several Bcl-2 family members in CD34(+) cells dependent on the cytokine stimulation given. The use of Bcl-x(L)-specific ribozymes suggested that Bcl-x(L) is important for survival but not for differentiation of erythroid progenitor cells.
Josefsen
D
D
Department of Immunology, Institute for Cancer Research, The Norwegian Radium Hospital, Montebello, Oslo, Norway. dag.josefsen@labmed.uio.no
Myklebust
J H
JH
Lømo
J
J
Sioud
M
M
Blomhoff
H K
HK
Smeland
E B
EB
D000328:Adult; D018952:Antigens, CD34; D015415:Biomarkers; D002454:Cell Differentiation; D019070:Cell Lineage; D002470:Cell Survival; D002478:Cells, Cultured; D015672:Erythroid Precursor Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004921:Erythropoietin / Q000494:pharmacology; D016179:Granulocyte Colony-Stimulating Factor / Q000494:pharmacology; D006098:Granulocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000096:biosynthesis*; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis*; D016337:RNA, Catalytic; D019089:Stem Cell Factor / Q000494:pharmacology; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
D018952:Antigens, CD34; C494826:BAX protein, human; C494811:BCL2L1 protein, human; D015415:Biomarkers; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D016337:RNA, Catalytic; D019089:Stem Cell Factor; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D004921:Erythropoietin; D016179:Granulocyte Colony-Stimulating Factor