Defective mast cell effector functions in mice lacking the CRACM1 pore subunit of store-operated calcium release–activated calcium channels

Abstract

CRACM1 (Orai1) constitutes the pore subunit of CRAC channels that are crucial for many physiological processes 1-6 . A point mutation in CRACM1 has been associated with SCID disease in humans 2 . We have generated CRACM1 deficient mice using gene trap, where β-galactosidase (LacZ) activity identifies CRACM1 expression in tissues. We show here that the homozygous CRACM1 deficient mice are considerably smaller in size and are grossly defective in mast cell degranulation and cytokine secretion. FcεRI-mediated in vivo allergic reactions were also inhibited in CRACM1-/-mice. Other tissues expressing truncated CRACM1-LacZ fusion protein include skeletal muscles, kidney and regions in the brain and heart. Surprisingly, no CRACM1 expression was seen in the lymphoid regions of thymus. Accordingly, we found no defect in T cell development. Thus, our data reveal novel crucial roles for CRAC channels including a putative role in excitable cells.

STIM1 and STIM2 protein deficiency in T lymphocytes underlies development of the exocrine gland autoimmune disease, Sjögren's syndrome

“…Studies in mice have also led to similar conclusions. Whereas global deletion of Orai1, STIM1, or STIM2 in mice results in premature death (12,28,29), T-cell-targeted deletion of both STIM1 and STIM2 leads to autoimmune symptoms. Decreased numbers of Tregs as well as compromised suppressive function of Tregs on effector T cells were noted in these mice, suggesting that Treg development appears to be especially sensitive to the absence of STIM-dependent Ca 2+ influx (12).…”

Plasticity in Ca 2+ selectivity of Orai1/Orai3 heteromeric channel

“…T-cells of patients with a severe combined immunodeficiency lacked CRAC currents due to non-functional Orai1 channels, caused by a single point mutation (6,(10)(11)(12). In line, Orai1 deficiency in mice impaired Ca 2ϩ influx and cytokine production in T cells (6), degranulation in mast cells (7), and thrombus formation of platelets (13,14). Store-operated channels (SOCs) observed in various cell types such as endothelial, smooth muscle, or epidermal cells differ in Ca 2ϩ selectivity and cation permeability (1).…”

“…Upon store depletion, the endoplasmic reticulum resident Ca 2ϩ sensor Stim1 multimerizes, redistributes and activates the three Orai channels (also termed CRACM) in the plasma membrane leading to highly Ca 2ϩ -selective currents (2)(3)(4)(5). Orai1 is strongly expressed in lymphoid organs, skeletal muscle, liver, and skin (6,7). While Orai3 is detected in similar tissues as Orai1, Orai2 is predominantly found in murine brain (8) or human kidney, lung, and spleen (9).…”

Store-Operated Calcium Channels: New Perspectives on Mechanism and Function

“…The first hints for a function came from observations that CRAC-deficient SCID patients display a mild muscle myopathy with reduced strength and endurance (Partiseti et al 1994;McCarl et al 2009). STIM1 and Orai1 were later shown to be highly expressed in both human and mouse skeletal muscle (Williams et al 2001;Gwack et al 2008;Stiber et al 2008;Vig et al 2008;McCarl et al 2009), and STIM1-deficient mice exhibit reduced muscle mass and susceptibility to fatigue (Stiber et al 2008). The reduced mass is presumably caused by a defect in muscle development, as knockdown of STIM1, STIM2, or Orai1 or 3 inhibits the differentiation of myoblasts into myotubes and underlying gene activation events (Darbellay et al 2008(Darbellay et al , 2010.…”

“…These findings have triggered intense interest in developing specific pharmacologic inhibitors of the CRAC channel to treat a variety of autoimmune disorders. In mice, the absence of Orai1 or STIM1 function causes multiple defects of cytokine expression in T cells (interleukin (IL)-2, interferon-g, IL-4, IL-10) Oh-Hora et al 2008), and in mast cells, defective synthesis or release of inflammatory mediators (tumor necrosis factor-a, IL-6, serotonin, and leukotriene C 4 ) leads to a reduced anaphylaxis response in vivo (Baba et al 2008;Vig et al 2008). B-cell targeted deletion of STIM1 and STIM2 revealed a novel role for SOCE in enabling B cells to limit autoimmunity; in these animals reduced secretion of the anti-inflammatory cytokine IL-10 was linked to increased severity of experimental autoimmune encephalomyelitis, a model for multiple sclerosis (Matsumoto et al 2011).…”