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J. Exp. Med.,
Volume 188, Number 3, August 3, 1998 439-450
By


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From the * Clinical Research Institute of Montreal, Montréal, Quebec H2W 1R7, Canada; the In normal hemopoietic cells that are dependent on specific growth factors for cell survival, the
expression of the basic helix-loop-helix transcription factor SCL/Tal1 correlates with that of
c-Kit, the receptor for Steel factor (SF) or stem cell factor. To address the possibility that SCL
may function upstream of c-kit, we sought to modulate endogenous SCL function in the
CD34+ hemopoietic cell line TF-1, which requires SF, granulocyte/macrophage colony-stimulating factor, or interleukin 3 for survival. Ectopic expression of an antisense SCL cDNA (as-SCL) or a dominant negative SCL (dn-SCL) in these cells impaired SCL DNA binding activity, and prevented the suppression of apoptosis by SF only, indicating that SCL is required for
c-Kit-dependent cell survival. Consistent with the lack of response to SF, the level of c-kit
mRNA and c-Kit protein was significantly and specifically reduced in as-SCL- or dn-SCL-
expressing cells. c-kit mRNA, c-kit promoter activity, and the response to SF were rescued by
SCL overexpression in the antisense or dn-SCL transfectants. Furthermore, ectopic c-kit expression in as-SCL transfectants is sufficient to restore cell survival in response to SF. Finally,
enforced SCL in the pro-B cell line Ba/F3, which is both SCL and c-kit negative is sufficient to induce c-Kit and SF responsiveness. Together, these results indicate that c-kit, a gene that is
essential for the survival of primitive hemopoietic cells, is a downstream target of the transcription factor SCL.
Department of Pharmacology, the § Department of Biochemistry, the
Department of Microbiology-Immunology, and ¶ The Program of Molecular Biology, University of Montreal, Montreal, Quebec
H3C 3J7, Canada; ** The National Cancer Institute, Naval Medical Center, Bethesda, Maryland
20892; 
The Department of Medicine, McGill University, Montreal, Quebec H3A 2A7, Canada;
and §§ Institut National de la Santé et de la Recherche Médicale U.91, Hôpital Henri Mondor,
94010 Créteil, France
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