Transforming growth factor-β prevents stem cell factor-mediated rescue of mast cells from apoptosis after IL-3 deprivation

IL-3-dependent mast cells undergo apoptosis upon removal of IL-3, an event that is prevented by the addition of stem cell factor (SCF) acting through its receptor c-kit, suggesting that SCF provides a mechanism to allow mast cells to survive and to differentiate in tissues in the relative absence of IL-3. This observation is consistent with the thesis that the microenvironment, in part, controls mast cell number and viability by modulating SCF production and release. The purpose of the present study was to determine whether a second factor, TGF-β1, was capable of modifying the SCF-mediated survival pathway. TGF-β1 (1 and 10 ng/ml), known to be an important regulator of cell growth and function, did inhibit the SCF-mediated rescue from apoptosis in IL-3-deprived mast cells. TGF-β1 exerted its inhibitory effect on SCF-mediated rescue from apoptosis, even when added 4 h after the addition of SCF. In contrast, TGF-β1 had no substantial effect on the viability of mast cells that were grown in the presence of IL-3. TGF-β1 also had no noticeable effect on viability and proliferation of a growth factor-independent mast cell line. The inhibitory effect of TGF-β1 was neutralized by specific anti-TGF-β mAb. TGF-β1 did not affect the expression of c-kit, as determined by using flow cytometric analysis of mast cells labeled with FITC-conjugated anti-c-kit. These results demonstrate how 'SCF and TGF-β may act in concert to regulate mast cell numbers under physiologic or pathologic conditions.