癌症相关钙网蛋白突变体 CRT Del52 的钙结合分子与功能分析
Molecular and functional analysis of calcium binding by a cancer-linked calreticulin mutant
与骨髓增殖性肿瘤相关的钙网蛋白突变体 CRT Del52 保留了低亲和力钙结合能力。研究用重组 CRT 蛋白经等温滴定量热法（ITC）测定，野生型 CRT 与 CRT Del52 的低亲和力钙结合特征相似，两者共有的 340–349 残基参与结合。在 CRT 敲除（CRT-KO）细胞中回补野生型 CRT 或 CRT Del52 后，内质网与胞质钙水平及钙库操纵性钙内流（SOCE）相当。CRT-KO 还会诱导多种已知含低亲和力钙结合位点或调控内质网钙水平的 ER 蛋白表达，提示 CRT 缺失引发代偿性细胞变化以维持内质网钙稳态。
来源：eLife · doi.org
Calreticulin (CRT) is an endoplasmic reticulum (ER) chaperone with low-affinity calcium-binding sites in its C-terminal domain. This region is altered by somatic mutations in the CRT gene ( CALR ), which drive a subset of myeloproliferative neoplasms (MPNs). Perturbations in ER calcium storage and signaling are reported for the MPN type I mutant, CRT Del52 , and are linked to disease pathogenesis. Using recombinant CRT proteins, we found similar low-affinity calcium-binding characteristics for wild-type CRT and CRT Del52 , as determined by isothermal titration calorimetry (ITC). Residues 340–349, conserved in both wild-type CRT and CRT Del52 , contribute to binding. Furthermore, ER and cytosolic calcium levels, and store-operated calcium entry (SOCE), were comparable in CRT knockout (CRT-KO) cells reconstituted with wild-type CRT or CRT Del52 . Notably, the CRT-KO induces expression of multiple ER proteins known to contain low-affinity calcium-binding sites or regulate ER calcium levels. Overall, these findings indicate that CRT Del52 retains at least some low-affinity calcium-binding capacity and that CRT deficiency induces compensatory cellular changes that maintain ER calcium homeostasis.