Involvement of Calpain in the Process of Jurkat T Cell Chemotaxis

T cell involvement in the disease process of multiple sclerosis (MS) (Hickey, 1991; McFarland and Martin, 2007) and its animal model experimental autoimmune encephalomyelitis (EAE) are well established (Waksman and Adams, 1962; Swanborg, 2001). T cell infiltration into the central nervous system (CNS) is greatly increased in the plaques of MS patients (Hickey, 1991) as well as of EAE animals immediately before the onset of pathological symptoms and during clinical course of the disease (Waksman and Adams, 1962). Increased activity and expression of the Ca2+-activated protease calpain has been demonstrated in inflammatory cells (Shields et al., 1998, 1999) during the disease state in EAE animals. Moreover, inhibition of calpain has been demonstrated to decrease the T cell infiltration during acute EAE (Hassen et al., 2006). Calpain has signaling functions and is involved in a multitude of cellular processes including apoptosis (Zhivotovsky et al., 1997), T cell activation (Penna et al., 1999; Schaecher et al., 2004), cell cycle (Janossy et al., 2004), and cell migration (Huttenlocher et al., 1997; Franco and Huttenlocher, 2005). T cell exclusion from the CNS is the therapeutic strategy used by the α4β1-integrin blocking monoclonal antibody natalizumab (Ransohoff, 2007), which has been approved by the U.S. Food and Drug Administration (FDA). However, use of the FDA-approved drug natalizumab has not been without problems including several patients on this medication developing progressive multi-focal leukoencephalopathy (Koralnik, 2006) leading to the temporary withdrawal of the drug from the market. In addition, alternative targets for MS therapy are urgently warranted as a result of the low effectiveness of many of the current standard therapies available (Kleinschnitz et al., 2007). Targeted exclusion of T cells from the CNS would be of great benefit not only to MS but also to many other autoimmune diseases that have a T cell component in their pathology, including rheumatoid arthritis (Cope et al., 2007) and amyotrophic lateral sclerosis (Graves et al., 2004). Inflammatory cells entering the CNS in MS and EAE have been shown to increase calpain levels (Shields et al., 1998). If calpain was indeed involved with T cell migration then calpain inhibition would provide an alternative method for reducing pathological T cell entry into the CNS. Calpain has been shown to be involved in the migration of numerous cell types including CHO cells (Huttenlocher et al., 1997), fibroblasts (Shiraha et al., 2002), myoblasts (Leloup et al., 2006), and neutrophils (Lokuta et al., 2003). The chemokine CCL2 (previously known as monocyte chemoattractant protein-1) and its predominant receptor CCR2, a G protein–coupled receptor, have been extensively associated with inflammatory pathologies (Jee et al., 2002; Mahad et al., 2006). CCL2 has been extensively shown as a specific chemoattractant for monocytes and T cells (Carr et al., 1994; Sanders et al., 2000). Even though the initiating stimulus for migration is well established, the downstream mechanism of T cell chemotaxis as of yet remains incomplete. In this study, our aim was to gather evidence for the involvement of calpain in the process of T cell migration. This analysis used the Jurkat E6-1 T cell line to model for T cells as well as the normal human peripheral blood mononuclear cells (PBMCs) to model for primary cells. We observed an increase in activity of calpain in response to the CCL2 stimulation as well as the restriction of role of calpain in involvement in the directed migration of chemotaxis. This is in contrast to other immune cell types where calpain has been demonstrated to play a role in the negative regulation of chemokinesis (Lokuta et al., 2003). Thus, our current study provides an evidence for the involvement of calpain in T cell chemotaxis. Further examination of calpain involvement in the chemotaxis of native T cells and pathological T cells from MS patients and EAE animals is supported by the findings of this study.