Synaptotagmin I expression in mast cells of normal human tissues, systemicmast cell disease, and a human mast cell leukemia cell line

Synaptotagmin I (STG I) is a Ca2+ sensor and one of the synaptic Vesicle pr oteins that mediate exocytosis. To determine the mechanism of release of la rge granules from mast cells, we studied by immunohistochemistry the presen ce of STG I in mast cells in normal human tissues simultaneously with the m ast cell markers mast cell tryptase (tryptase) and c-kit. The tumor cells o f systemic mast cell disease (SMCD) and a human mast cell leukemia cell lin e (HMC-1) were also examined. Human mast cells in normal tissues and the tu mor cells of SMCD expressed STG I as well as mast cell tryptase (tryptase) and c-kit. STG I mRNA and its products in HMC-1 were examined by RT-PCR ana lysis and immunocytochemistry, respectively. STG I expression in HMC-1 cell s was compared with that in cells stimulated and non-stimulated by phorbol 12-myristate 13-acetate and also with that in NB-1 and PC12 cells, known to express STG I. STG I mRNA was detected in both non-stimulated and stimulat ed HMC-1 cells and in NB-1 and PC12 cells. STG I immunoreactivity was weake r than NB-1 or PC12 immunoreactivity. However, it increased in the stimulat ed HMC-1 cells. Mast cells expressed STG I in various states. STG I may med iate exocytosis of large granules in mast cells.