Am. J. Respir. Cell Mol. Biol., Vol 15, No. 3, Sep 1996, 355-360.
Specific inhibition of beta-tryptase expression in a human mast cell line by granulocyte-macrophage colony-stimulating factor produced by airways structural cells
S Finotto, JS Marshall, JH Butterfield and JA Denburg
Department of Medicine, McMaster University, Hamilton, Ontario, Canada.
The growth and differentiation of mast cells are regulated by cytokines
produced in tissue microenvironments. We previously reported that mast
cells isolated from the epithelial compartment of nasal polyp tissue
contain significantly less tryptase when compared with mast cells isolated
from the stroma of the same tissue. In an attempt to explore this finding,
we analyzed the ability of supernatants obtained from cultured nasal polyp
epithelial cells (NP-EpCM) or nasal polyp fibroblasts (NP-FbCM) to regulate
the tryptase content of the immature human mast cell line HMC-1. HMC-1
cells were cultured for 7 days in Iscove's modified Dulbecco's medium
(IMDM) with 30% of either NP-FbCM or NP-EpCM or 20% MoCM (supernatant of a
leukemic T cell line). As assessed by radioimmunoassay and test for
enzymatic activity, all three conditioned media were shown to significantly
decrease tryptase protein expression in HMC-1, when compared with cultures
performed with IMDM alone (NP-EpCM P < 0.001; NP-FbCM P < 0.04; MoCM
P < 0.004). In addition, Northern blot analysis demonstrated lower
tryptase mRNA levels upon exposure to all three conditioned media tested,
suggesting that tryptase downregulation occurs at the transcriptional
level. In further studies we found that preincubation of MoCM with anti-
granulocyte-macrophage colony-stimulating factor (GM-CSF) completely
blocked the observed downregulation of tryptase expression mediated by this
conditioned medium. The findings suggest that GM-CSF has a suppressive
effect on expression of protease in mast cells, and may thus play a
modulatory role in determining the extent of tissue inflammation in
allergic airways disease.
