Winrow C J, Miyata K S, Marcus S L, Burns K, Michalak M, Capone J P, Rachubinski R A
Department of Anatomy and Cell Biology, University of Alberta, Edmonton, Canada.
Mol Cell Endocrinol. 1995 Jun;111(2):175-9. doi: 10.1016/0303-7207(95)03563-m.
Calreticulin is a ubiquitous calcium binding/storage protein found primarily in the endoplasmic reticulum. Calreticulin has been shown to inhibit DNA binding and transcriptional activation by glucocorticoid and androgen hormone receptors by binding to the conserved sequence KXFF(K/R)R, present in the DNA-binding domains of all known members of the steroid/nuclear hormone receptor superfamily. To determine whether calreticulin might be a general regulator of hormone-responsive pathways, we examined its effect on DNA binding in vitro and transcriptional activation in vivo by heterodimers of the peroxisome proliferator-activated receptor (PPAR) and the 9-cis retinoic acid receptor (RXR alpha). We show here that purified calreticulin inhibits the binding of PPAR/RXR alpha heterodimers and of other nuclear hormone receptors, to peroxisome proliferator-responsive DNA elements in vitro. However, overexpression of calreticulin in transiently transfected cultured cells had little or no effect on transactivation mediated by PPAR/RXR alpha. Therefore, while calreticulin inhibits the binding of both nuclear and steroid hormone receptors to cognate response elements in vitro, our findings suggest that calreticulin does not necessarily play an important role in the regulation of all classes of hormone receptors in vivo.
钙网蛋白是一种主要存在于内质网中的普遍存在的钙结合/储存蛋白。已表明钙网蛋白通过与存在于类固醇/核激素受体超家族所有已知成员的DNA结合域中的保守序列KXFF(K/R)R结合，来抑制糖皮质激素和雄激素受体的DNA结合及转录激活。为了确定钙网蛋白是否可能是激素反应途径的一般调节因子，我们检测了它对过氧化物酶体增殖物激活受体（PPAR）和9-顺式视黄酸受体（RXRα）异二聚体的体外DNA结合及体内转录激活的影响。我们在此表明，纯化的钙网蛋白在体外抑制PPAR/RXRα异二聚体及其他核激素受体与过氧化物酶体增殖物反应性DNA元件的结合。然而，在瞬时转染的培养细胞中过表达钙网蛋白对PPAR/RXRα介导的反式激活几乎没有影响。因此，虽然钙网蛋白在体外抑制核激素受体和类固醇激素受体与同源反应元件的结合，但我们的研究结果表明，钙网蛋白在体内不一定在所有类型激素受体的调节中发挥重要作用。
