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Caspase, a family of cysteine proteases, serve as effectors in apoptosis. The ced3 gene in C.elegans was first identified to be involved in apoptosis. This gene encodes the ced-3 caspase that is similar to the interleukin-1-beta converting enzyme or ICE in mammals. In addition to apoptosis, caspases also function in the inflammatory response. Inflammatory caspases are essential in activating pro-inflammatory cytokines that recruit immune cells and block the replication of pathogens inside cells.
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G protein-coupled receptor (GPCR) signaling plays a crucial role in cell functioning. GPCR desensitization is an equally essential process. It allows cells to respond to changing environments and regain sensitivity to new stimuli while preventing unnecessary stimulation when no longer needed. Prolonged exposure to stimuli leads to GPCR desensitization. It involves blocking the receptors from binding and activating additional G proteins. This inhibits activation of downstream effectors, thereby...
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Related Experiment Video

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A Colorimetric Assay that Specifically Measures Granzyme B Proteolytic Activity: Hydrolysis of Boc-Ala-Ala-Asp-S-Bzl
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Granzyme K activates protease-activated receptor-1.

Dawn M Cooper1, Dmitri V Pechkovsky, Tillie L Hackett

  • 1Institute for Heart and Lung Health, St. Paul's Hospital, Vancouver, British Columbia, Canada.

Plos One
|July 16, 2011
PubMed
Summary

Granzyme K (GrK) activates protease-activated receptor-1 (PAR-1) in lung fibroblasts, driving the release of pro-inflammatory cytokines and increasing cell proliferation, revealing a novel non-cytotoxic role in inflammation.

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Area of Science:

  • Immunology
  • Cell Biology
  • Biochemistry

Background:

  • Granzyme K (GrK), a serine protease, is implicated in sepsis and acute lung inflammation.
  • Previously considered solely pro-apoptotic, GrK may have non-cytotoxic functions.
  • The role of extracellular GrK in initiating inflammatory responses via protease-activated receptors (PARs) is under investigation.

Purpose of the Study:

  • To investigate the non-cytotoxic effects of extracellular Granzyme K on human lung fibroblasts.
  • To determine if GrK activates PARs, leading to pro-inflammatory cytokine release and cellular signaling.
  • To elucidate the specific PARs and intracellular pathways involved in GrK-mediated responses.

Main Methods:

  • Cultured human lung fibroblasts were treated with purified extracellular Granzyme K.
  • Cytokine secretion (IL-6, IL-8, MCP-1) was measured using ELISA.
  • Intracellular signaling pathways (ERK1/2, p38 MAP kinase) were assessed.
  • Fibroblast proliferation was quantified.
  • Neutralizing antibodies against PAR-1 and PAR-2 were employed.

Main Results:

  • Extracellular Granzyme K induced dose- and time-dependent release of IL-6, IL-8, and MCP-1.
  • Protease activity of GrK was essential for cytokine release, as heat-inactivated GrK had no effect.
  • GrK activated ERK1/2 and p38 MAP kinase signaling pathways.
  • GrK significantly increased fibroblast proliferation, an effect abrogated by ERK1/2 inhibition.
  • PAR-1 activation was identified as essential for GrK-induced cytokine release.

Conclusions:

  • Extracellular Granzyme K acts as a non-cytotoxic mediator in acute lung inflammation.
  • GrK activates PAR-1 on lung fibroblasts, triggering pro-inflammatory cytokine secretion.
  • GrK also promotes fibroblast proliferation via MAP kinase signaling, highlighting its multifaceted role in inflammatory processes.