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Transforming growth factor beta 1 inhibits expression of the gene products for steel factor and its receptor (c-kit)
M C Heinrich1, D C Dooley, W W Keeble
1Department of Medicine, Oregon Health Sciences University, Portland, USA.
Abstract:
Transforming growth factor beta 1 (TGF-beta 1), a product of marrow stromal cells, inhibits the proliferation and differentiation of hematopoietic progenitor cells within the hematopoietic microenvironment. Steel factor (SF), also a product of marrow stromal cells, is an essential positive regulator of hematopoiesis in vivo. TGF-beta 1 has been shown to repress human and murine leukemic cell and murine lin- bone marrow mononuclear cell expression of the receptor for SF (c-kit). We speculated that TGF-beta 1 might exert its inhibitory effect on hematopoiesis in part by decreasing SF/c-kit interactions. Therefore, we tested the hypothesis that TGF-beta 1 inhibits both stromal cell expression of SF and hematopoietic progenitor cell expression of c-kit. We measured stromal cell expression of SF protein and hematopoietic progenitor cell expression of membrane-bound c-kit before and after exposure to recombinant human TGF-beta 1. Both stromal cell expression of SF protein and hematopoietic progenitor cell expression of c-kit protein were inhibited 50% to 80% by TGF-beta 1. Using Northern blot and ribonuclease protection assays, we determined that TGF-beta 1 repressed stromal cell SF mRNA, but did not alter SF transcript stability. TGF-beta 1 was also found to repress c-kit mRNA in human leukemic myeloblasts as well as in normal lin- hematopoietic progenitor cells. In contrast with its effect on SF mRNA, TGF-beta 1 accelerated the degradation of c-kit mRNA. We conclude that TGF-beta 1 inhibits stromal cell production of SF by repression of SF gene transcription and represses hematopoietic progenitor cell expression of c-kit by decreasing the stability of c-kit transcripts. Taking into account the importance of SF and c-kit in maintaining steady-state hematopoiesis in vivo, the dual effect of TGF-beta 1 on both SF and c-kit gene expression is likely to be one of the major mechanisms by which TGF-beta 1 inhibits hematopoiesis in vivo.
Insights
Transforming growth factor beta 1 (TGF-beta 1) inhibits hematopoiesis by reducing Steel factor (SF) and c-kit expression. This growth factor impacts both stromal cell SF production and hematopoietic progenitor cell c-kit levels, affecting blood cell formation.
Area of Science:
- Hematology
- Molecular Biology
- Cell Biology
Background:
- Transforming growth factor beta 1 (TGF-beta 1) is a key regulator produced by marrow stromal cells that influences hematopoietic progenitor cell proliferation and differentiation.
- Steel factor (SF) is another critical stromal cell product essential for in vivo hematopoiesis.
- TGF-beta 1 has been observed to downregulate the expression of c-kit, the receptor for SF, on various cell types, including leukemic cells and hematopoietic progenitor cells.
Purpose of the Study:
- To investigate the hypothesis that TGF-beta 1 inhibits hematopoiesis by reducing the interaction between SF and c-kit.
- To determine if TGF-beta 1 affects the expression of SF by stromal cells and c-kit by hematopoietic progenitor cells.
- To elucidate the molecular mechanisms by which TGF-beta 1 modulates SF and c-kit expression.
Main Methods:
- Measurement of stromal cell SF protein and hematopoietic progenitor cell c-kit protein levels before and after exposure to recombinant human TGF-beta 1.
- Northern blot analysis and ribonuclease protection assays to assess SF and c-kit mRNA levels and stability in response to TGF-beta 1.
- Evaluation of TGF-beta 1's impact on SF gene transcription and c-kit transcript stability.
Main Results:
- TGF-beta 1 significantly inhibited both stromal cell SF protein (50-80%) and hematopoietic progenitor cell c-kit protein (50-80%) expression.
- TGF-beta 1 repressed SF mRNA in stromal cells, indicating an effect on gene transcription, but did not alter SF transcript stability.
- TGF-beta 1 repressed c-kit mRNA in both leukemic myeloblasts and normal hematopoietic progenitor cells, and accelerated c-kit mRNA degradation, suggesting an impact on transcript stability.
Conclusions:
- TGF-beta 1 inhibits stromal cell production of SF primarily by repressing SF gene transcription.
- TGF-beta 1 inhibits hematopoietic progenitor cell expression of c-kit by decreasing the stability of c-kit transcripts.
- The dual action of TGF-beta 1 on both SF and c-kit gene expression represents a significant mechanism contributing to its inhibitory effects on in vivo hematopoiesis.