Structure and evolutionary origin of the human granzyme H gene

Abstract

Among the molecules proposed to be involved in cytotoxic T lymphocyte (CTL), natural killer (NK) and lymphokine activated killer (LAK) cell-mediated lysis are the granzymes, a family of serine proteases stored in the cytoplasmic granules of CTLs, NK and LAK cells. In addition to the granzymes A and B, a third member of this family has been cloned in man and designated granzyme H. We present the complete gene sequence including the 5' promoter region and demonstrate that the granzyme H sequence represents a functional gene expressed in activated T cells. Granzyme H shows the highest degree (>54%) of amino acid sequence homology with granzyme B and cathepsin G and, like these genes, consists of five exons separated by introns at equivalent positions. The evolutionary history of granzyme H has been analyzed by reconstructing an evolutionary tree for granzyme sequences. We provide evidence that interlocus recombination between the ancestral genes of granzyme B and granzyme H occurred about 21 million years ago, leading to a replacement of exon 3, intron 3 and part of exon 4 in human granzyme H by human granzyme B sequences. Our results suggest that the ancestral gene of granzyme H is more closely related to cathepsin G and granzyme B than to the murine granzymes C to G. Thus, granzyme H does not represent a human counterpart of the known murine granzymes A to G. It diverged from cathepsin G before mammalian radiation and should, therefore, exist in other mammalian lineages as well.

Discordant Regulation of Granzyme H and Granzyme B Expression in Human Lymphocytes

“…The cellular expression of gzm H has been reported in just one study that assessed gzm H mRNA expression in human T cells (10). This study concluded that like gzm B, gzm H is expressed at high levels in activated T cells.…”

“…Gzm M preferentially cleaves at residues with long, uncharged side chains (Met, Leu), and its gene is closely linked to the neutrophil elastase gene on human chromosome 19 (9). The genes for gzms B and H are located on chromosome 14, tightly linked with the gene encoding cathepsin G, another chymotrypsin-like protease ("chymase") that, unlike the gzms, is expressed in cells of the myeloid lineage but not in lymphocytes (7,10). These three genes all map to within 60 kb of one another.…”

“…Gzm H has a very high amino acid identity (Ͼ90%) with many portions of the gzm B sequence, particularly near the amino terminus of the molecule (10) despite performing a distinct enzymic function. It has been inferred from the high degree of sequence similarity that the gzmH gene arose by duplication of part of the 5Ј end of the gzmB gene (particularly exons 3 and 4) and fusion with the 3Ј end of an another primordial serine protease gene (10).…”

Neutrophils: Molecules, Functions and Pathophysiological Aspects

“…Genomic cloning has revealed that neutrophil elastase, proteinase 3, and azurocidin genes form a cluster of genes, located in the terminal region of the short arm of chromosome 19 and coordinately regulated in the promonocytic cell line U937 during induced terminal differentiation (Sturrock et al, 1992;Zimmer et al, 1992). The gene of cathepsin G belongs to another cluster of genes encoding hematopoietic serine proteases along with granzyme H and granzyme B genes on chromosome 14q11.2 (Haddad et al, 1991;Hanson et al, 1990).…”

Cleavage of La protein by granzyme H induces cytoplasmic translocation and interferes with La-mediated HCV-IRES translational activity

“…7 Although gzmB and cathepsin G are highly conserved between human and mice, the precise functional ortholog of human gzmH has not been determined. 8 Interestingly, gzmH is constitutively expressed in NK cells irrespective of the activation status, and in contrast to GzmB, it is not present in activated CD8 þ T cells, 9,10 suggesting that gzmH might play a critical role in the cytotoxic arm of the innate immune response. GzmH has chymotrypsin-like (chymase) activity and is capable of cleaving synthetic substrates with a clear preference of Phe and Tyr in the P 1 site.…”