CAML Is a p56Lck-Interacting Protein that Is Required for Thymocyte Development

Abstract

Calcium modulating cyclophilin ligand (CAML) is a ubiquitously expressed protein implicated in T cell signaling, although its mechanism and physiologic role in the immune system are unknown. We show here that CAML is essential for peripheral T cell development. Inactivation of CAML in mouse thymocytes lowered the numbers of double-positive and single-positive thymocytes, concomitant with reduced positive and enhanced negative selection. We found that CAML interacts with p56Lck and appears to regulate subcellular localization of the kinase in both resting and T cell receptor (TCR)-stimulated cells. CAML-deficient cells displayed enhanced p56lck and ZAP-70 phosphorylation and increased IL2 production and cell death after TCR stimulation, suggesting that CAML may act as a negative regulator of p56lck. Our data establish a novel role for CAML as an essential mediator of T cell survival during thymopoiesis and indicate that its loss deregulates p56Lck signaling.

Calcium-Modulating Cyclophilin Ligand Is Essential for the Survival of Activated T Cells and for Adaptive Immunity

“…The following Abs were used for Western blot: CAML-specific Ab was described previously (14) and actin (C4; Millipore). For the ER stress protein expression experiment, whole-cell lysates were extracted with radioimmunoprecipitation assay buffer (1% nonylphenoxypolyethoxyethanol, 0.25% sodium deoxycholate, 50 mM Tris [pH 7.5], 150 mM NaCl, and 5 mM EDTA).…”

Calcium-modulating cyclophilin ligand regulates membrane trafficking of postsynaptic GABAA receptors

“…Knock-out mice with a global deletion of CAML exhibit early embryonic lethality that precludes preparation and analyses of neurons cultured from corresponding embryos. Therefore, to further investigate the function of CAML biochemically, we took advantage of mice with a CAML locus that is flanked (floxed) by loxP sites (Tran et al, 2005). CAML-mutant neurons were prepared using 4-hydroxytamoxifen-induced conditional deletion of the CAML gene from differentiated neuron cultures derived from CAGGCre-ER™ × CAML f/f or CAGGCre-ER™ × CAML f/-embryos (for mating scheme to generate these embryos, see Experimental Methods).…”

“…Knockout mice with a deletion of the CAML gene in the germ line (CAML +/-or CAML -/-, Tran et al, 2003) and the mouse line containing a floxed CAML allele (CAML f/f , Tran et al, 2005) have been previously described. CAGGCre-ER™ transgenic mice (Hayashi and McMahon, 2002) were obtained from JAX mice (Bar Harbor, ME).…”

“…CAML was originally described as a cyclophilin B-binding protein whose overexpression in Jurkat T cells causes a rise in intracellular calcium, thus activating transcription factors responsible for the early immune response (Bram and Crabtree, 1994;Holloway and Bram, 1996). Subsequent work showed that CAML is involved in intracellular trafficking of diverse receptors and signaling proteins and essential for thymocyte development (Tran et al, 2005;Tran et al, 2003;von Bulow and Bram, 1997). CAML is an endoplasmic reticulum (ER)-resident integral membrane protein that contains a hydrophilic N-terminal cytoplasmic domain, followed by three putative transmembrane domains (Holloway and Bram, 1998).…”

Cancer-Induced Signaling Defects in Antitumor T Cells

“…For example, modification of target p56 lck to obviate accessibility to Shp-1 could prevent kinase inactivation in spite of activation and recruitment of Shp-1. Although such a function for known p56 lck -binding proteins (e.g., LIME (Brdickova et al, 2003;Hur et al, 2003), CAML (Tran et al, 2005)) has not been described, shielding from Shp-1 access by a non-p56 lck protein is conceivable. However, an induced conformational change in a Shp-1 binding domain (SH2) in p56 lck has been reported which results from phosphorylation of p56 lck Ser 59 by ERK (Stefanova et al, 2003).…”