Holloway M P, Bram R J
Department of Experimental Oncology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
J Biol Chem. 1998 Jun 26;273(26):16346-50. doi: 10.1074/jbc.273.26.16346.
The calcium-modulating cyclophilin ligand (CAML) protein activates Ca2+ influx signaling when overexpressed in Jurkat T cells. Although CAML appears to directly participate in Ca2+-dependent signaling initiated by the transmembrane activator and CAML interactor cell surface receptor, its mechanism of action is unknown. To address this issue, we have determined its membrane topology, subcellular localization, and ability to mobilize intracellular Ca2+ pools. Fractionation of cell extracts on discontinuous sucrose gradients and indirect immunofluorescence indicate that CAML co-localizes with sarcoplasmic/endoplasmic reticulum calcium/ATPase-2 and calreticulin at membrane-bound cytosolic vesicles. Limited trypsin digests indicate that the hydrophilic NH2-terminal domain of CAML is directed toward the cytoplasm. Functionally, CAML overexpression was shown to deplete thapsigargin-sensitive intracellular Ca2+ pools. These data suggest that CAML may initiate Ca2+ signaling through activation of a capacitative Ca2+ influx pathway.
钙调节亲环蛋白配体（CAML）蛋白在Jurkat T细胞中过表达时可激活Ca2+内流信号。尽管CAML似乎直接参与由跨膜激活剂和CAML相互作用细胞表面受体引发的Ca2+依赖性信号传导，但其作用机制尚不清楚。为了解决这个问题，我们确定了其膜拓扑结构、亚细胞定位以及动员细胞内Ca2+池的能力。在不连续蔗糖梯度上对细胞提取物进行分级分离和间接免疫荧光表明，CAML与肌浆网/内质网钙/ATP酶-2和钙网蛋白共定位于膜结合的胞质囊泡。有限的胰蛋白酶消化表明，CAML的亲水性NH2末端结构域指向细胞质。在功能上，CAML过表达被证明可耗尽毒胡萝卜素敏感的细胞内Ca2+池。这些数据表明，CAML可能通过激活容量性Ca2+内流途径来启动Ca2+信号传导。
