Blessing or curse? Proteomics in granzyme research

Abstract

Granzymes (gzms) are a group of serine proteases that play an important role in innate and adaptive immunity, blood coagulation, apoptosis, and inflammation, but are also connected to atherosclerosis, diabetes, cardiovascular and inflammatory lung diseases, cancer, and sepsis. Humans have five gzms (gzms A, B, H, K, and M), which differ in their substrate specificity. It is widely accepted that they are delivered from cytotoxic lymphocytes via perforin into the cytoplasm of target cells where they initiate cell death, modulate cytokine signaling, or inactivate pathogen proteins. However, more recent evidence indicates gzms also act extracellularly in noncytotoxic processes. Proteomic approaches are directed at mapping gzm cleavage specificity, identifying substrates, and unraveling the (patho-) physiological role of these proteases. These studies have refined our understanding of gzm species specificity, and collectively uncovered an enormous number of new substrates. However, with the exception of a very few human gzmB substrates supported by independent data (Bid, DNA-PK, PARP, ICAD, and procaspase 7), it is presently unclear which are physiologically relevant. This review aims to summarize and analyze the different proteomic approaches used and discuss both their convincing and controversial outcomes.

Antigen-specific primed cytotoxic T cells eliminate tumour cells in vivo and prevent tumour development, regardless of the presence of anti-apoptotic mutations conferring drug resistance

“…From in vitro studies, it seems clear that gzmB presents the highest cytotoxic potential among all gzms and readily induces apoptosis in most types of target cells [1][2][3][4]. Several gzmB substrates have been identified in vitro, but only a few of them have been confirmed to be relevant during Tc-mediated and/or NK cell-mediated cell death [3,5,6]. GzmB activates apoptosis in vitro by direct cleavage of procaspase 3 to generate the active effector enzyme [7], and by activating the intrinsic mitochondrial pathway, initiated after cleaving Bid to generate the truncated active form tBid [8,9].…”

Phenotypic and Functional Characteristics of Microvesicles Produced by Natural Killer Cells

“…Granzyme B (GrB) is a serine proteinase initiating the apoptosis in the target cell due to the activation of the mitochondrial pathway, the activation of effector caspases (the most common pathway for a mouse cell), or the splitting of intracellular substrates (ROCKI, α-tubulin, filamin, etc.) [22,24,61]. (Patho) physiological properties of GrB were also described: extracellular matrix breakdown (activity toward vitronectin, fibronectin, and laminin), participation in the proinflammatory reaction induction through IL-1α breakdown [24], splitting of C3 and C5 components of a complement [49], and modulation of coagulation processes due to the effect of the von Willebrand factor on the expression [24].…”

“…[22,24,61]. (Patho) physiological properties of GrB were also described: extracellular matrix breakdown (activity toward vitronectin, fibronectin, and laminin), participation in the proinflammatory reaction induction through IL-1α breakdown [24], splitting of C3 and C5 components of a complement [49], and modulation of coagulation processes due to the effect of the von Willebrand factor on the expression [24]. GrB can be stimulated by IL-1β, IL-18, TNFα, IFNα, IFNγ, PMA, and LPS.…”

Granzyme K‐deficient mice show no evidence of impaired antiviral immunity

“…Recent proteomic studies however show that the extended substrate specificity of GzmK is distinct from granzyme A, strongly suggesting it targets different substrates and has a distinct biological role 18 , 19 , 20 . Unfortunately, these studies do not identify candidate physiological substrates 21 …”

“…[18][19][20] Unfortunately, these studies do not identify candidate physiological substrates. 21 Here, we take an important step toward to resolving the biological role(s) of GzmK in immunity by generating and analyzing Gzmk-null mice. We find no evidence for a role in CTL cytotoxcity or antiviral immunity.…”