Stem cell factor is localized in, released from, and cleaved by human mastcells

Stem cell factor (SCF) is the most important cytokine regulating human mast cell growth and functions. The immunogold technique showed SCF in the secr etory granules of skin mast cells and in lung parenchymal mast cells (HLMC) , Immunoreactive SCF (iSCF) was detected in cell lysates of HLMC, but not i n basophils; iSCF and histamine were detected in supernatants of HLMC 3 min after challenge with anti-Fc epsilon RI or anti-IgE, and iSCF in snpernata nts rapidly declined after 30 min, whereas histamine remained unchanged for 120 min, HPLC and: electrospray mass spectrometry (ES/MS) analysis of reco mbinant human SCF1-166 (18,656.9 +/- 0.9 Da) treated with chymase showed a polypeptide of 17,977.1 +/- 0.6 Da and a minor component of 697.4 +/- 0.1 D a generated by specific cleavage at Phe159, SCF1-166 and SCF1-159 similarly activated HLMC, potentiated anti-IgE induced activation of these cells, an d stimulated HLMC chemotaxis. SCF159-166 had effect on mast cells. Western blot analysis of supernatants of anti-IgE-activated HLMC incubated with rec ombinant human SCF1-166 showed that SCF1-166 was rapidly cleaved to SCF1-15 9 and SCF1-144, Experiments with supernatants of anti-IgE-activated HLMC in cubated with SCF1-166 yielded similar results. In conclusion, SCF is stored in mast cell secretory granules and is immunologically released by human m ast cells. SCF1-166 is rapidly and specifically cleaved to SCF1-159 by chym ase, which retains its biological effect on mast cells, SCF is also cleaved by other proteases to several SCF species whose possible biological activi ties remain to be established.