Background: Alpha-tryptase and beta-tryptase are important clinical markers for mast cell-dependent disorders. A third family of tryptase genes on human chromosome 16 has been identified and called human mouse mast cell protease 7 (hmMCP-7)-like tryptase.
Objective: This study was designed to determine whether these tryptase genes 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 most genomes and whether it was expressed.
Results: The tryptase clone was almost identical to the hmMCP-7-like tryptase II and I genes, and therefore it was called hmMCP-7-like tryptase III. All such genes encode a Gln(-3) like alpha-tryptase. They also terminate translation after amino acid 235, whereas alpha- and beta-tryptase genes each 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 lung cells contained hmMCP-7-like tryptases in their genomes by PCR with gene-specific primers. To identify whether such genes were transcriptionally active, RT-PCR revealed alpha- or beta-tryptase products in all mast cell preparations and cell lines and in activated skin-derived mast cells, but no hmMCP-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-tryptases.