TGF-β1 Attenuates Mediator Release and De Novo Kit Expression by Human Skin Mast Cells through a Smad-Dependent Pathway

Abstract

TGF-beta has pleiotropic effects on many cell types at different stages of their development, including mast cells. The present study examines the effects of TGF-beta on human skin mast cells of the MC(TC) type. The expression of TGF-beta receptors (TGF-R) was verified at the mRNA and protein levels for TGF-RI and TGF-RII, and at the mRNA level for accessory molecules beta-glycan and endoglin. TGF-beta did not affect mast cell viability after 1 wk at concentrations < or = 10 ng/ml, but at 50 ng/ml caused significant cell death. TGF-beta inhibited surface and total expression of Kit in a dose-dependent manner, whereas the surface expression of Fc epsilonRI, Fc gammaRI, and Fc gammaRII was not affected. TGF-beta inhibited degranulation and cytokine production, but not PGD(2) production. TGF-beta diminished surface Kit expression through a TGF-RI kinase/Smad-dependent pathway by inhibiting new synthesis of Kit protein, which became evident following internalization and degradation of Kit after mast cells were exposed to the Kit ligand, stem cell factor. In contrast, addition of TGF-beta had no discernible effect on surface Kit expression when administered 3 days after stem cell factor, by which time surface Kit levels had returned to baseline. Although both transcription and translation are important for de novo expression of Kit, Kit mRNA levels were not affected by TGF-beta. Therefore, transcription of a gene other than Kit might be involved in Kit expression. Finally, activation of mast cells increased their susceptibility to TGF-beta-mediated apoptosis, a process that might regulate the survival of activated mast cells in vivo.