Granzyme K (GrK) is a protein that is encoded by the GZMKgene on chromosome 5 in humans.[5][6]Granzymes are a family of serine proteases which have various intracellular and extracellular roles. GrK is found in granules of natural killer (NK) cells and cytotoxic T lymphocytes (CTLs), and is traditionally described as being cytotoxic towards targeted foreign, infected, or cancerous cells. NK cells and CTLs can induce apoptosis through the granule secretory pathway, which involves the secretion of granzymes along with perforin at immunological synapses.
Intracellularly, GrK may cleave a variety of substrates, such as the nucleosome assembly protein (NAP),[7] HMG2,[7] and Ape1[8] in the ER-associated SET complex, along with other targets that have downstream cytotoxic effects. Compared to in vitro studies of GrK cytotoxicity in rats and humans, in vitro mouse studies show no cytotoxic potential in the absence of perforin, making the role of GrK controversial.[9][10]In vitro studies show potential extracellular targets for GrK such as the cleavage and activation of protease activated receptors (PAR)-1[11][12] and PAR-2.[13] Grk binds lipopolysaccharides (LPS)in vitro separately from GrK's catalytic activity.[14] Both PAR and LPS activation by GrK induce cytokine production in human in vitro studies.
GrK is important in bacterial and viral[15] infection control. GrK-expressing CD8+ T cells may be associated with inflammation and aging.[16]
^ abZhao T, Zhang H, Guo Y, Zhang Q, Hua G, Lu H, Hou Q, Liu H, Fan Z (March 2007). "Granzyme K cleaves the nucleosome assembly protein SET to induce single-stranded DNA nicks of target cells". Cell Death and Differentiation. 14 (3): 489–499. doi:10.1038/sj.cdd.4402040. PMID17008916. S2CID6044972.
^Guo Y, Chen J, Zhao T, Fan Z (April 2008). "Granzyme K degrades the redox/DNA repair enzyme Ape1 to trigger oxidative stress of target cells leading to cytotoxicity". Molecular Immunology. 45 (8): 2225–2235. doi:10.1016/j.molimm.2007.11.020. PMID18179823.
^Susanto O, Trapani JA, Brasacchio D (December 2012). "Controversies in granzyme biology". Tissue Antigens. 80 (6): 477–487. doi:10.1111/tan.12014. PMID23137319.
Hameed A, Lowrey DM, Lichtenheld M, Podack ER (November 1988). "Characterization of three serine esterases isolated from human IL-2 activated killer cells". Journal of Immunology. 141 (9): 3142–3147. doi:10.4049/jimmunol.141.9.3142. PMID3262682.
Baker E, Sayers TJ, Sutherland GR, Smyth MJ (1994). "The genes encoding NK cell granule serine proteases, human tryptase-2 (TRYP2) and human granzyme A (HFSP), both map to chromosome 5q11-q12 and define a new locus for cytotoxic lymphocyte granule tryptases". Immunogenetics. 40 (3): 235–237. doi:10.1007/BF00167085. PMID8039831. S2CID37615055.
Sayers TJ, Lloyd AR, McVicar DW, O'Connor MD, Kelly JM, Carter CR, Wiltrout TA, Wiltrout RH, Smyth MJ (May 1996). "Cloning and expression of a second human natural killer cell granule tryptase, HNK-Tryp-2/granzyme 3". Journal of Leukocyte Biology. 59 (5): 763–768. doi:10.1002/jlb.59.5.763. PMID8656064. S2CID18065724.
Zhao T, Zhang H, Guo Y, Zhang Q, Hua G, Lu H, Hou Q, Liu H, Fan Z (March 2007). "Granzyme K cleaves the nucleosome assembly protein SET to induce single-stranded DNA nicks of target cells". Cell Death and Differentiation. 14 (3): 489–499. doi:10.1038/sj.cdd.4402040. PMID17008916. S2CID6044972.
