title: Transforming growth factor-beta regulates c-kit message stability and cell-surface protein expression in hematopoietic progenitors.
abstract: The cell-surface receptor c-kit and its cognate ligand stem-cell factor (SCF) or steel factor (SLF) are important for the maintenance of hematopoiesis both in vitro and in vivo. Transforming growth factor-beta (TGF-beta) has been shown to be a potent inhibitor of SLF-mediated synergistic growth of murine Lin-Sca-1+ progenitor cells, as well as more committed progenitors. In the present study, we examined the regulation of c-kit mRNA and cell-surface expression by TGF-beta. Among the murine hematopoietic progenitor cells tested, the myeloid cell line FDC-P1 and the mast-cell line MC-6, as well as progenitor-enriched bone marrow cells, constitutively expressed functional cell-surface c-kit. Treatment of these progenitor cell lines and primary progenitor cells with TGF-beta resulted in downregulation of cell-surface c-kit expression. This effect was not a secondary event of cell-cycle status. TGF-beta inhibition was dose- and time-dependent, with 50% inhibition seen between 0.3 to 3 ng/mL TGF-beta and maximal inhibition at 30 ng/mL. Using the FDC-P1 cell line, we observed that the inhibition of cell-surface c-kit expression by TGF-beta is preceded by a marked reduction in c-kit mRNA levels starting 2 hours after TGF-beta treatment, and reaches a maximum by 6 hours. The inhibition in steady-state c-kit mRNA levels is explained, in part, by a decrease in the half-life of c-kit transcripts (2 to 4 hours for control cells v 0.5 to 1.5 hours for TGF-beta-treated cells). These findings suggest that TGF-beta regulates the responsiveness of murine hematopoietic progenitors to SLF through a decrease in c-kit message stability leading to decreased cell-surface expression.
authors.affiliation: Faculty of Medicine, Department of Pediatrics, University of Sherbrooke, Québec, Canada.
authors.forename: C M
authors.initials: CM
authors.lastname: Dubois
authors.forename: F W
authors.initials: FW
authors.lastname: Ruscetti
authors.forename: J
authors.initials: J
authors.lastname: Stankova
authors.forename: J R
authors.initials: JR
authors.lastname: Keller
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000187:drug effects; D002460:Cell Line; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects*; D016298:Hematopoietic Cell Growth Factors / Q000494:pharmacology; D006412:Hematopoietic Stem Cells / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D011518:Proto-Oncogene Proteins / Q000032:analysis / Q000235:genetics*; D019009:Proto-Oncogene Proteins c-kit; D012333:RNA, Messenger / Q000378:metabolism*; D020794:Receptor Protein-Tyrosine Kinases / Q000032:analysis / Q000235:genetics*; D016184:Receptors, Colony-Stimulating Factor / Q000032:analysis / Q000235:genetics*; D019089:Stem Cell Factor; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
chemical_list: D016298:Hematopoietic Cell Growth Factors; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D016184:Receptors, Colony-Stimulating Factor; D019089:Stem Cell Factor; D016212:Transforming Growth Factor beta; D019009:Proto-Oncogene Proteins c-kit; D020794:Receptor Protein-Tyrosine Kinases