SELECTIVE REPORTER EXPRESSION IN MAST-CELLS USING A CHYMASE PROMOTER

Primate alpha-chymases are mast cell neutral proteases that are involv ed in regulating several regulatory peptides including angiotensin II. Because of significant substrate specificity differences among the ch ymase group of enzymes, animal models that overexpress primate chymase s are crucial for delineating the in vivo function of these enzymes. A ctivation of alpha-prochymase requires processing enzymes and proteogl ycans found in mast cell secretory granules. Thus, the development of models overexpressing active primate chymase requires a mast cell-spec ific promoter. We show that the 571-base pair (bp) 5'-upstream sequenc e of the baboon chymase gene, which encodes an alpha-chymase, coupled to the prokaryotic lacZ gene allows the targeting of beta-galactosidas e to mast cells in transgenic mice. Tissue expression of the transgene is similar to the expression of the endogenous mouse alpha-chymase mo use mast cell protease-5. A mouse mast cell line that endogenously exp resses mouse mast cell protease-5 (JKras mast cells) also selectively supports the expression of this transgene. In vitro transcription stud ies in JKras mast cells shows the critical role of a GATA cis-regulato ry motif in baboon chymase promoter, located similar to 430-bp upstrea m of the transcription start site. These results suggest that the 571- bp domain of the baboon chymase promoter contains most, if not all, of the mast cell-specific region of the promoter. We describe here for t he first time a promoter that directs expression of transgenes specifi cally to mouse mast cells. This promoter should be generally applicabl e for dominant expression of mast cell regulatory proteins.