MOUSE MAST-CELL PROTEASE-9, A NOVEL MEMBER OF THE CHROMOSOME-14 FAMILY OF SERINE PROTEASES THAT IS SELECTIVELY EXPRESSED IN UTERINE MAST-CELLS

Mouse mast cell protease (mMCP) 1, mMCP-2, mMCP-4, and mMCP-5 are memb ers of a family of related serine proteases whose genes reside within an similar to 850 kilobase (kb) complex on chromosome 14 that does not readily undergo crossover events, While mapping the mMCP-1 gene, we i solated a novel gene that encodes a homologous serine protease designa ted mMCP-9. The mMCP-9 and mMCP-1 genes are only similar to 7 kb apart on the chromosome and are oriented back to back, The proximity of the mMCP-1 and mMCP-9 genes now suggests that the low recombination frequ ency of the complex is due to the closeness of some of its genes, The mMCP-9 transcript and protein were observed in the jejunal submucosa o f Trichinella spiralis-infected BALB/c mice, However, in normal BALB/c mice, mMCP-9 transcript and protein were found only in those mast cel ls that reside in the uterus, Thus, the expression of mMCP-9 differs f rom that of all other chymases. The observation that BALB/c mouse bone marrow-derived mast cells developed with interleukin (IL) 10 and c-ki f ligand contain mMCP-9 transcript, whereas those developed with IL-3 do not, indicates that the expression of this particular chymase is re gulated by the cytokine microenvironment, Comparative protein structur e modeling revealed that mMCP-9 is the only known granule protease wit h three positively charged regions on its surface. This property may a llow mMCP-9 to form multimeric complexes with serglycin proteoglycans and other negatively charged proteins inside the granule, Although mMC P-9 exhibits a >50% overall amino acid sequence identity with its homo logous chymases, it has a unique substrate-binding cleft, This finding suggests that each member of the chromosome 14 family of serine prote ases evolved to degrade a distinct group of proteins.