Transforming growth factor-beta(1) induces apoptosis in CD34(+)CD38(-/low) cells that express Bcl-2 at a low level

Exp Hematol. 2001 Sep;29(9):1098-108. doi: 10.1016/s0301-472x(01)00680-4.


Objective: Transforming growth factor-beta(1) (TGF-beta(1)) strongly inhibits the proliferation and differentiation of primitive CD34(+)CD38(-) hematopoietic cells. In contrast, Flt3 ligand (FL) is a positive effector of CD34(+)CD38(-/low) cell proliferation. Because apoptosis plays a critical role in hematopoietic development, TGF-beta(1) and FL were analyzed as possible modulators of apoptosis. Specifically, this report examined expression of apoptotic promoters Bax and Bad and apoptotic inhibitors Bcl-2 and Bcl-x (all members of the Bcl-2 protein family). Protein levels were determined in fresh and cultured CD34(+)CD38(+) cells and CD34(+)CD38(-/low) cells with and without treatment with TGF-beta(1) and FL.

Materials and methods: Cells fractions were purified by sorting CD34(+)-enriched mononuclear cells from mobilized peripheral blood. Expression of Bcl-2, Bcl-x, Bax, and Bad and the extent of apoptosis were determined by flow cytometric analysis of freshly isolated cells and cells cultured with TGF-beta(1) and FL effectors.

Results: TGF-beta(1) reduced CD34(+)CD38(+) cell expansion and arrested cell division. Inhibition of growth was not accompanied by an increase in apoptosis. In CD34(+)CD38(-)(/low) cells, serum TGF-beta(1) and added TGF-beta(1) inhibited cell growth and significantly increased apoptotic cell death. Freshly isolated CD34(+)CD38(+) and CD34(+)CD38(-/low) cells expressed Bcl-2 at similar low levels. However, after 3 days, Bcl-2 expression was markedly higher in cultured CD34(+)CD38(+) cells. TGF-beta(1) significantly increased Bax expression in both fractions after 3 days cultivation (p = 0.0034). Thus, addition of TGF beta-1 further reduced the already low Bcl-2:Bax ratio in CD34(+)CD38(-/low) cells.

Conclusions: Compared to CD34(+)CD38(+) cells, CD34(+)CD38(-/low) cells were slow to up-regulate expression of Bcl-2 during ex vivo culture. TGF-beta(1) up-regulated Bax expression by both CD34(+)CD38(+) and CD34(+)CD38(-)(/low) cells and promoted apoptosis in the latter fraction. This suggests that the preferential induction of apoptosis in primitive cells by TGF-beta(1) may be due to its further reduction of the Bcl-2:Bax ratio.

MeSH terms

  • ADP-ribosyl Cyclase
  • ADP-ribosyl Cyclase 1
  • Antigens, CD*
  • Antigens, CD34 / blood*
  • Antigens, Differentiation / blood*
  • Apoptosis / drug effects*
  • Carrier Proteins / drug effects
  • Carrier Proteins / metabolism
  • Cell Division / drug effects
  • Flow Cytometry
  • Hematopoietic Stem Cells / drug effects*
  • Hematopoietic Stem Cells / immunology
  • Hematopoietic Stem Cells / metabolism
  • Humans
  • Membrane Glycoproteins
  • Membrane Proteins / metabolism
  • Membrane Proteins / pharmacology
  • NAD+ Nucleosidase / blood*
  • Proto-Oncogene Proteins / drug effects
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins c-bcl-2 / drug effects
  • Proto-Oncogene Proteins c-bcl-2 / metabolism*
  • Transforming Growth Factor beta / pharmacology*
  • Transforming Growth Factor beta1
  • bcl-2-Associated X Protein
  • bcl-Associated Death Protein
  • bcl-X Protein


  • Antigens, CD
  • Antigens, CD34
  • Antigens, Differentiation
  • BAD protein, human
  • BAX protein, human
  • BCL2L1 protein, human
  • Carrier Proteins
  • Membrane Glycoproteins
  • Membrane Proteins
  • Proto-Oncogene Proteins
  • Proto-Oncogene Proteins c-bcl-2
  • TGFB1 protein, human
  • Transforming Growth Factor beta
  • Transforming Growth Factor beta1
  • bcl-2-Associated X Protein
  • bcl-Associated Death Protein
  • bcl-X Protein
  • flt3 ligand protein
  • ADP-ribosyl Cyclase
  • CD38 protein, human
  • NAD+ Nucleosidase
  • ADP-ribosyl Cyclase 1