title: Bromelain, from pineapple stems, proteolytically blocks activation of extracellular regulated kinase-2 in T cells.
abstract: Recently, it has emerged that extracellular proteases have specific regulatory roles in modulating immune responses. Proteases may act as signaling molecules to activate the Raf-1/extracellular regulated kinase (ERK)-2 pathway to participate in mitogenesis, apoptosis, and cytokine production. Most reports on the role of protease-mediated cell signaling, however, focus on their stimulatory effects. In this study, we show for the first time that extracellular proteases may also block signal transduction. We show that bromelain, a mixture of cysteine proteases from pineapple stems, blocks activation of ERK-2 in Th0 cells stimulated via the TCR with anti-CD3epsilon mAb, or stimulated with combined PMA and calcium ionophore. The inhibitory activity of bromelain was dependent on its proteolytic activity, as ERK-2 inhibition was abrogated by E-64, a selective cysteine protease inhibitor. However, inhibitory effects were not caused by nonspecific proteolysis, as the protease trypsin had no effect on ERK activation. Bromelain also inhibited PMA-induced IL-2, IFN-gamma, and IL-4 mRNA accumulation, but had no effect on TCR-induced cytokine mRNA production. This data suggests a critical requirement for ERK-2 in PMA-induced cytokine production, but not TCR-induced cytokine production. Bromelain did not act on ERK-2 directly, as it also inhibited p21ras activation, an effector molecule upstream from ERK-2 in the Raf-1/MEK/ERK-2 kinase signaling cascade. The results indicate that bromelain is a novel inhibitor of T cell signal transduction and suggests a novel role for extracellular proteases as inhibitors of intracellular signal transduction pathways.
authors.affiliation: Department of Biochemistry, Imperial College of Science, Technology and Medicine, London, United Kingdom. t.mynott@ic.ac.uk
authors.forename: T L
authors.initials: TL
authors.lastname: Mynott
authors.forename: A
authors.initials: A
authors.lastname: Ladhams
authors.forename: P
authors.initials: P
authors.lastname: Scarmato
authors.forename: C R
authors.initials: CR
authors.lastname: Engwerda
mesh_terms: D000818:Animals; D001963:Bromelains / Q000378:metabolism / Q000494:pharmacology* / Q000633:toxicity; D002470:Cell Survival / Q000187:drug effects / Q000276:immunology; D004789:Enzyme Activation / Q000187:drug effects / Q000276:immunology; D004791:Enzyme Inhibitors / Q000378:metabolism / Q000494:pharmacology* / Q000633:toxicity; D005638:Fruit / Q000201:enzymology; D006801:Humans; D006825:Hybridomas; D006868:Hydrolysis / Q000187:drug effects; D007376:Interleukin-2 / Q000235:genetics / Q000378:metabolism; D019169:Jurkat Cells; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D015689:Oncogene Protein p21(ras) / Q000037:antagonists & inhibitors; D010766:Phosphorylation / Q000187:drug effects; D018547:Plant Stems / Q000201:enzymology; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000037:antagonists & inhibitors / Q000502:physiology; D013601:T-Lymphocytes / Q000187:drug effects / Q000201:enzymology*; D014443:Tyrosine / Q000037:antagonists & inhibitors
chemical_list: D004791:Enzyme Inhibitors; D007376:Interleukin-2; D012333:RNA, Messenger; D011948:Receptors, Antigen, T-Cell; D014443:Tyrosine; D001963:Bromelains; D019950:Mitogen-Activated Protein Kinase 1; D015689:Oncogene Protein p21(ras)