Human mouse mast cell protease 7-like tryptase genes are pseudogenes

Background: alpha -Tryptase and beta -tryptase are important clinical marke rs for mast cell-dependent disorders. A third family of tryptase genes on h uman chromosome 16 has been identified and called human mouse mast cell pro tease 7 (hmMCP-7)-like tryptase. Objective: This study was designed to determine whether these tryptase gene s are expressed by human mast cells. Methods: A 2842-bp hmMCP-7-like tryptase gene was cloned and sequenced from a human placental genomic library. PCR and RT-PCR procedures, respectively , were used to determine whether this tryptase gene family was present in m ost genomes and whether it was expressed. Results: The tryptase clone was almost identical to the hmMCP-7-like trypta se II and I genes, and therefore it was called hmMCP-7-like tryptase III. A ll such genes encode a Gln(-3) like alpha -tryptase. They also terminate tr anslation after amino acid 235, whereas alpha- and beta -tryptase genes eac h encode a 275-amino acid protein. In this study, cell lines HMC-1, KU812, and Mono-Mac-6; mast cells derived in vitro from cord blood and fetal liver progenitors; and mast cell-enriched preparations of dispersed skin and lun g cells contained hmMCP-7-like tryptases in their genomes by PCR with gene- specific primers. To identify whether such genes were transcriptionally act ive, RT-PCR revealed alpha- or beta -tryptase products in all mast cell pre parations and cell lines and in activated skin-derived mast cells, but no h mMCP-7-like tryptase products. Conclusion: These results indicate hmMCP-7-like tryptase (I, II, III) genes are pseudogenes and unlikely to affect measurements of alpha- and beta -tr yptases.