Selective reporter expression in mast cells using a chymase promoter.

Primate alpha-chymases are mast cell neutral proteases that are involved in regulating several regulatory peptides including angiotensin II. Because of significant substrate specificity differences among the chymase group of enzymes, animal models that overexpress primate chymases are crucial for delineating the in vivo function of these enzymes. Activation of alpha-prochymase requires processing enzymes and proteoglycans found in mast cell secretory granules. Thus, the development of models overexpressing active primate chymase requires a mast cell-specific promoter. We show that the 571-base pair (bp) 5'-upstream sequence of the baboon chymase gene, which encodes an alpha-chymase, coupled to the prokaryotic lacZ gene allows the targeting of beta-galactosidase to mast cells in transgenic mice. Tissue expression of the transgene is similar to the expression of the endogenous mouse alpha-chymase mouse mast cell protease-5. A mouse mast cell line that endogenously expresses mouse mast cell protease-5 (JKras mast cells) also selectively supports the expression of this transgene. In vitro transcription studies in JKras mast cells shows the critical role of a GATA cis-regulatory motif in baboon chymase promoter, located approximately 430-bp upstream 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 the first time a promoter that directs expression of transgenes specifically to mouse mast cells. This promoter should be generally applicable for dominant expression of mast cell regulatory proteins.