Differential Expression of Bcl‐2 Homologs in Human CD34+ Hematopoietic Progenitor Cells Induced to Differentiate into Erythroid or Granulocytic Cells

• Published in: Stem cells (Dayton, Ohio) Ohio), 2000-01, Vol.18 (4), p.261-272
• Main Authors: Josefsen, Dag, Myklebust, June H., Lømo, Jon, Sioud, Mouldy, Blomhoff, Heidi K., Smeland, Erlend B.
• Format: Article
• Language: English
• Subjects: Adult; Antigens, CD34; Apoptosis; bcl-2-Associated X Protein; bcl-X Protein; Bcl‐2; Bcl‐xL; Biomarkers; CD34+ cells; Cell Differentiation; Cell Lineage; Cell Survival; Cells, Cultured; Erythroid Precursor Cells - cytology; Erythroid Precursor Cells - drug effects; Erythroid Precursor Cells - metabolism; Erythropoiesis; Erythropoietin - pharmacology; Granulocyte Colony-Stimulating Factor - pharmacology; Granulocytes - cytology; Granulocytes - drug effects; Granulocytes - metabolism; Hematopoiesis; Hematopoietic Stem Cells - cytology; Hematopoietic Stem Cells - drug effects; Hematopoietic Stem Cells - metabolism; Human; Humans; Myeloid Cell Leukemia Sequence 1 Protein; Neoplasm Proteins - biosynthesis; Proto-Oncogene Proteins - biosynthesis; Proto-Oncogene Proteins c-bcl-2 - biosynthesis; RNA, Catalytic; Stem Cell Factor - pharmacology
• ISSN: 1066-5099; 1549-4918
• DOI: 10.1634/stemcells.18-4-261

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‐xL protein expression and downregulation of Bax expression, apparent from day 4 and more pronounced on days 8 and 21. In contrast, Bcl‐xL 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‐xL in early erythroid differentiation was further examined by use of specific ribozymes against Bcl‐xL. Addition of Bcl‐xL 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‐xL‐specific ribozymes suggested that Bcl‐xL is important for survival but not for differentiation of erythroid progenitor cells.