Mesaeli N, Nakamura K, Zvaritch E, Dickie P, Dziak E, Krause K H, Opas M, MacLennan D H, Michalak M
Medical Research Council Group in Molecular Biology of Membranes, Department of Biochemistry, University of Alberta, Canada.
J Cell Biol. 1999 Mar 8;144(5):857-68. doi: 10.1083/jcb.144.5.857.
Calreticulin is a ubiquitous Ca2+ binding protein, located in the endoplasmic reticulum lumen, which has been implicated in many diverse functions including: regulation of intracellular Ca2+ homeostasis, chaperone activity, steroid-mediated gene regulation, and cell adhesion. To understand the physiological function of calreticulin we used gene targeting to create a knockout mouse for calreticulin. Mice homozygous for the calreticulin gene disruption developed omphalocele (failure of absorption of the umbilical hernia) and showed a marked decrease in ventricular wall thickness and deep intertrabecular recesses in the ventricular walls. Transgenic mice expressing a green fluorescent protein reporter gene under the control of the calreticulin promoter were used to show that the calreticulin gene is highly activated in the cardiovascular system during the early stages of cardiac development. Calreticulin protein is also highly expressed in the developing heart, but it is only a minor component of the mature heart. Bradykinin-induced Ca2+ release by the InsP3-dependent pathway was inhibited in crt-/- cells, suggesting that calreticulin plays a role in Ca2+ homeostasis. Calreticulin-deficient cells also exhibited impaired nuclear import of nuclear factor of activated T cell (NF-AT3) transcription factor indicating that calreticulin plays a role in cardiac development as a component of the Ca2+/calcineurin/NF-AT/GATA-4 transcription pathway.
钙网蛋白是一种普遍存在的钙离子结合蛋白，位于内质网腔中，参与多种不同的功能，包括：调节细胞内钙离子稳态、伴侣活性、类固醇介导的基因调控以及细胞黏附。为了了解钙网蛋白的生理功能，我们利用基因打靶技术创建了钙网蛋白基因敲除小鼠。钙网蛋白基因破坏的纯合小鼠出现脐膨出（脐疝吸收失败），心室壁厚度显著降低，心室壁小梁间深陷。利用在钙网蛋白启动子控制下表达绿色荧光蛋白报告基因的转基因小鼠，表明钙网蛋白基因在心脏发育早期在心血管系统中高度激活。钙网蛋白在发育中的心脏中也高度表达，但它只是成熟心脏中的次要成分。缓激肽通过InsP3依赖性途径诱导的钙离子释放在crt-/-细胞中受到抑制，这表明钙网蛋白在钙离子稳态中起作用。钙网蛋白缺陷细胞还表现出活化T细胞核因子（NF-AT3）转录因子的核输入受损，这表明钙网蛋白作为Ca2+/钙调磷酸酶/NF-AT/GATA-4转录途径的一个组成部分在心脏发育中起作用。
