CALR

钙网蛋白是一种多功能蛋白，在内质网管腔内起主要钙（2+）结合（储存）蛋白的作用。它也在细胞核中发现，表明它可能在转录调节中起作用。钙网蛋白与合成肽klgfkr结合，后者几乎与核受体超家族的DNA结合域中的一个氨基酸序列相同。钙网蛋白与系统性狼疮和干燥病人的某些血清中的抗体结合，这些血清中含有抗Ro/SSA抗体，在物种间高度保守，位于内质和肌浆网中，可与钙结合。钙网蛋白的氨基末端与糖皮质激素受体的DNA结合域相互作用，阻止该受体与其特定的糖皮质激素反应元件结合。钙网蛋白能抑制雄激素受体与其激素反应性DNA元件的结合，抑制体内雄激素受体和维甲酸受体的转录活性，以及维甲酸诱导的神经元分化。因此，钙网蛋白可以作为调节核激素受体基因转录的重要调节剂。系统性红斑狼疮与对钙网蛋白的自身抗体滴度升高有关，但钙网蛋白不是一种RO/SS-A抗原。早先的论文提到钙网状蛋白是一种反渗透/反渗透-A抗原，但这后来被驳倒了。对人钙网蛋白的自身抗体滴度增加见于患有完全先天性心脏传导阻滞的婴儿，包括IgG和IgM两类。
Calreticulin is a multifunctional protein that acts as a major Ca(2+)-binding (storage) protein in the lumen of the endoplasmic reticulum. It is also found in the nucleus, suggesting that it may have a role in transcription regulation. Calreticulin binds to the synthetic peptide KLGFFKR, which is almost identical to an amino acid sequence in the DNA-binding domain of the superfamily of nuclear receptors. Calreticulin binds to antibodies in certain sera of systemic lupus and Sjogren patients which contain anti-Ro/SSA antibodies, it is highly conserved among species, and it is located in the endoplasmic and sarcoplasmic reticulum where it may bind calcium. The amino terminus of calreticulin interacts with the DNA-binding domain of the glucocorticoid receptor and prevents the receptor from binding to its specific glucocorticoid response element. Calreticulin can inhibit the binding of androgen receptor to its hormone-responsive DNA element and can inhibit androgen receptor and retinoic acid receptor transcriptional activities in vivo, as well as retinoic acid-induced neuronal differentiation. Thus, calreticulin can act as an important modulator of the regulation of gene transcription by nuclear hormone receptors. Systemic lupus erythematosus is associated with increased autoantibody titers against calreticulin but calreticulin is not a Ro/SS-A antigen. Earlier papers referred to calreticulin as an Ro/SS-A antigen but this was later disproven. Increased autoantibody titer against human calreticulin is found in infants with complete congenital heart block of both the IgG and IgM classes.