Centre for Regenerative Medicine "Stefano Ferrari", Department of Life Sciences, University of Modena and Reggio Emilia, Modena, Italy.
CRIMM, Center for Research and Innovation for Myeloproliferative Neoplasms, Department of Experimental and Clinical Medicine, AOU Careggi, University of Florence, Florence, Italy.
Sci Rep. 2019 Jul 22;9(1):10558. doi: 10.1038/s41598-019-46843-z.
Somatic mutations of calreticulin (CALR) have been described in approximately 60-80% of JAK2 and MPL unmutated Essential Thrombocythemia and Primary Myelofibrosis patients. CALR is an endoplasmic reticulum (ER) chaperone responsible for proper protein folding and calcium retention. Recent data demonstrated that the TPO receptor (MPL) is essential for the development of CALR mutant-driven Myeloproliferative Neoplasms (MPNs). However, the precise mechanism of action of CALR mutants haven't been fully unraveled. In this study, we showed that CALR mutants impair the ability to respond to the ER stress and reduce the activation of the pro-apoptotic pathway of the unfolded protein response (UPR). Moreover, our data demonstrated that CALR mutations induce increased sensitivity to oxidative stress, leading to increase oxidative DNA damage. We finally demonstrated that the downmodulation of OXR1 in CALR-mutated cells could be one of the molecular mechanisms responsible for the increased sensitivity to oxidative stress mediated by mutant CALR. Altogether, our data identify novel mechanisms collaborating with MPL activation in CALR-mediated cellular transformation. CALR mutants negatively impact on the capability of cells to respond to oxidative stress leading to genomic instability and on the ability to react to ER stress, causing resistance to UPR-induced apoptosis.
钙网织蛋白（CALR）的体细胞突变已在大约 60-80%的 JAK2 和 MPL 未突变的原发性血小板增多症和原发性骨髓纤维化患者中被描述。CALR 是内质网（ER）伴侣蛋白，负责正确的蛋白质折叠和钙保留。最近的数据表明，TPO 受体（MPL）对于 CALR 突变驱动的骨髓增殖性肿瘤（MPN）的发展至关重要。然而，CALR 突变体的精确作用机制尚未完全阐明。在这项研究中，我们表明 CALR 突变体损害了对 ER 应激的反应能力，并降低了未折叠蛋白反应（UPR）促凋亡途径的激活。此外，我们的数据表明，CALR 突变诱导对氧化应激的敏感性增加，导致氧化 DNA 损伤增加。我们最后证明，CALR 突变细胞中 OXR1 的下调可能是突变 CALR 介导的氧化应激增加敏感性的分子机制之一。总之，我们的数据确定了与 MPL 激活协同作用的新机制，在 CALR 介导的细胞转化中。CALR 突变体对细胞应对氧化应激的能力产生负面影响，导致基因组不稳定，并对 ER 应激的反应能力产生负面影响，导致对 UPR 诱导的细胞凋亡产生抗性。
