title: Activation of LFA-1 by ionomycin is independent of calpain-mediated talin cleavage.
abstract: Activation of calpains by calcium flux leading to talin cleavage is thought to be an important process of LFA-1 activation by inside-out signalling. Here, we tested the effects of the calcium ionophore ionomycin and calpain inhibitor calpeptin on LFA-1-mediated adhesion of a T cell hybridoma line, cytotoxic T cells and primary resting T cells. Ionomycin activated LFA-1-mediated adhesion of all three types of T cells, and calpeptin inhibited the effects of ionomycin. However, calpeptin also inhibited activation of LFA-1 by PMA, which did not induce calcium flux. Cleavage of talin was undetectable in ionomycin-treated T cells. Furthermore, treatment with ionomycin and calpeptin induced apoptosis of T cells. Inhibitors of phosphatidyl Inositol-3 kinase inhibited activation of LFA-1 by ionomycin, but not by PMA, whereas the protein kinase C inhibitor inhibited the effects of PMA, but not ionomycin. Thus, activation of LFA-1 by ionomycin is independent of calpain-mediated talin cleavage.
authors.affiliation: Terry Fox Laboratory, British Columbia Cancer Agency, Vancouver, BC, Canada V5Z 1L3.
authors.forename: Lisa
authors.initials: L
authors.lastname: Dreolini
authors.forename: Fumio
authors.initials: F
authors.lastname: Takei
mesh_terms: D000179:Acrylates / Q000494:pharmacology; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002448:Cell Adhesion / Q000187:drug effects / Q000502:physiology; D045744:Cell Line, Tumor; D002867:Chromones / Q000494:pharmacology; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004151:Dipeptides / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D006825:Hybridomas; D015759:Ionomycin / Q000494:pharmacology*; D007476:Ionophores / Q000494:pharmacology; D016169:Lymphocyte Function-Associated Antigen-1 / Q000502:physiology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009025:Morpholines / Q000494:pharmacology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011948:Receptors, Antigen, T-Cell / Q000235:genetics / Q000502:physiology; D013601:T-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D016608:Talin / Q000378:metabolism*; D000077191:Wortmannin
chemical_list: D000179:Acrylates; D000730:Androstadienes; D002867:Chromones; D015853:Cysteine Proteinase Inhibitors; D004151:Dipeptides; D004791:Enzyme Inhibitors; D007476:Ionophores; D016169:Lymphocyte Function-Associated Antigen-1; D009025:Morpholines; C100442:PD 150606; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011948:Receptors, Antigen, T-Cell; D016608:Talin; C071482:calpeptin; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D015759:Ionomycin; D011493:Protein Kinase C; D002154:Calpain; D000077191:Wortmannin