title: Calpain 4 is not necessary for LFA-1-mediated function in CD4+ T cells.
abstract: BACKGROUND
  T cell activation and immune synapse formation require the appropriate activation and clustering of the integrin, LFA-1. Previous work has reported that the calpain family of calcium-dependent proteases are important regulators of integrin activation and modulate T cell adhesion and migration. However, these studies have been limited by the use of calpain inhibitors, which have known off-target effects.
  
  
  RESULTS
  Here, we used a LoxP/CRE system to specifically deplete calpain 4, a small regulatory calpain subunit required for expression and activity of ubiquitously expressed calpains 1 and 2, in CD4+ T cells. CD4+ and CD8+ T cells developed normally in Capn4(F/F):CD4-CRE mice and had severely diminished expression of Calpain 1 and 2, diminished talin proteolysis and impaired casein degradation. Calpain 4-deficient T cells showed no difference in adhesion or migration on the LFA-1 ligand ICAM-1 compared to control T cells. Moreover, there was no impairment in conjugation between Capn4(F/F):CD4-CRE T cells and antigen presenting cells, and the conjugates were still capable of polarizing LFA-1, PKC-theta and actin to the immune synapse. Furthermore, T cells from Capn4(F/F):CD4-CRE mice showed normal proliferation in response to either anti-CD3/CD28 coated beads or cognate antigen-loaded splenocytes. Finally, there were no differences in the rates of apoptosis following extrinsic and intrinsic apoptotic stimuli.
  
  
  CONCLUSIONS
  Our findings demonstrate that calpain 4 is not necessary for LFA-1-mediated adhesion, conjugation or migration. These results challenge previous reports that implicate a central role for calpains in the regulation of T cell LFA-1 function.
authors.affiliation: University of Wisconsin, Madison, Wisconsin, United States of America.
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Wernimont
authors.forename: William T N
authors.initials: WT
authors.lastname: Simonson
authors.forename: Peter A
authors.initials: PA
authors.lastname: Greer
authors.forename: Christine M
authors.initials: CM
authors.lastname: Seroogy
authors.forename: Anna
authors.initials: A
authors.lastname: Huttenlocher
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology / Q000201:enzymology* / Q000276:immunology*; D002154:Calpain / Q000378:metabolism*; D002448:Cell Adhesion / Q000276:immunology; D002465:Cell Movement / Q000276:immunology; D049109:Cell Proliferation; D054992:Immunological Synapses / Q000276:immunology; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism*; D051379:Mice
chemical_list: D016169:Lymphocyte Function-Associated Antigen-1; D002154:Calpain; C410233:Capns1 protein, mouse