title: Perforin lytic activity is controlled by calreticulin.
abstract: The components within cytotoxic lymphocyte granules are responsible for a significant fraction of T and NK cell-mediated death. Perforin is stored in these granules together with calreticulin. Calreticulin has long been recognized as a chaperone protein of the endoplasmic reticulum (ER) and is the only resident ER protein to be found in the cytotoxic granules. Here we implicate a role for calreticulin in killing and report that it controls osmotic lysis mediated by purified perforin. Calreticulin, at a concentration of 2.2 x 10-7 M, completely blocked perforin-mediated lysis. Inhibition was stable and held over 5 h. Recombinant calreticulin, at a concentration of 8. 8 x 10-7 M, also blocked lysis, indicating the inhibition was due to calreticulin and not a copurifying protein in the native calreticulin preparations. Using calreticulin domain fragments (expressed as GST fusion proteins), we found inhibitory activity in the high-capacity calcium-binding C-domain, which does not bind perforin. The N- or P-domains, which can bind perforin, were unable to block lysis. The inhibition of lysis was independent of granzyme inactivation or the ability of calreticulin to sequester calcium. Our data indicate that calreticulin regulation of perforin-mediated lysis probably occurs without direct interaction with perforin. We propose a novel model in which calreticulin stabilizes membranes to prevent polyperforin pore formation.
authors.affiliation: Cell and Molecular Biology Program, School of Medicine and College of Agriculture, University of Nevada, Reno, NV 89557, USA. saf@scs.unr.edu
authors.forename: S A
authors.initials: SA
authors.lastname: Fraser
authors.forename: R
authors.initials: R
authors.lastname: Karimi
authors.forename: M
authors.initials: M
authors.lastname: Michalak
authors.forename: D
authors.initials: D
authors.lastname: Hudig
mesh_terms: D000818:Animals; D002118:Calcium / Q000037:antagonists & inhibitors / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D037282:Calreticulin; D002155:Calsequestrin / Q000494:pharmacology; D053818:Chymases; D003602:Cytotoxicity, Immunologic / Q000187:drug effects / Q000235:genetics / Q000276:immunology*; D004285:Dogs; D004306:Dose-Response Relationship, Immunologic; D008562:Membrane Glycoproteins / Q000037:antagonists & inhibitors* / Q000276:immunology / Q000633:toxicity*; D054353:Perforin; D052899:Pore Forming Cytotoxic Proteins; D017434:Protein Structure, Tertiary / Q000502:physiology; D051381:Rats; D011916:Rats, Inbred F344; D011994:Recombinant Proteins / Q000494:pharmacology; D012261:Ribonucleoproteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D012697:Serine Endopeptidases / Q000378:metabolism; D013997:Time Factors
chemical_list: D002135:Calcium-Binding Proteins; D037282:Calreticulin; D002155:Calsequestrin; D008562:Membrane Glycoproteins; D052899:Pore Forming Cytotoxic Proteins; D011994:Recombinant Proteins; D012261:Ribonucleoproteins; D054353:Perforin; D012697:Serine Endopeptidases; D053818:Chymases; D002118:Calcium