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

Abstract

Background: α-Tryptase and β-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 α-tryptase. They also terminate translation after amino acid 235, whereas α- and β-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 α- or β-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 α- and β-tryptases. (J Allergy Clin Immunol 2001;107:315-21.)