Daitoku Shinya, Takenaka Katsuto, Yamauchi Takuji, Yurino Ayano, Jinnouchi Fumiaki, Nunomura Takuya, Eto Tetsuya, Kamimura Tomohiko, Higuchi Masakazu, Harada Naoki, Saito Noriyuki, Miyamoto Toshihiro, Iwasaki Hiromi, Akashi Koichi
Department of Medicine and Biosystemic Science, Kyushu University Graduate School of Medical Sciences, Fukuoka, Japan.
Department of Hematology, Hamanomachi Hospital, Fukuoka, Japan.
Exp Hematol. 2016 Sep;44(9):817-825.e3. doi: 10.1016/j.exphem.2016.05.001. Epub 2016 May 13.
Somatic mutations of calreticulin (CALR) have been observed in many cases of essential thrombocythemia (ET) or primary myelofibrosis that harbor non-mutated Janus kinase 2 (JAK2). CALR mainly localizes within the endoplasmic reticulum lumen, but a small fraction of the total CALR pool is distributed over the cell surface. Cell surface CALR is known to transduce prophagocytic "eat me" signals to macrophages and acts as one of the important regulators for macrophage engulfment. In this study, we attempted to clarify whether mutant CALR may affect the threshold for macrophage engulfment and play an integral role in the pathogenesis of CALR-mutated ET. First, we compared the surface expression levels of CALR on hematopoietic stem and progenitor cells (HSPCs) and mature blood cells in patients with myeloproliferative neoplasms and found that the surface expression of mutant CALR did not change. Next, we compared the threshold for macrophage phagocytosis of each HSPC fraction and mature blood cells and found no significant change in the efficiency of macrophage engulfment. Our data suggest that CALR mutation does not affect sensitivity to phagocytosis by macrophages. Finally, we analyzed the phosphorylation statuses of molecules downstream of JAK2 at each HSPC level in patients with ET and found that CALR mutations activated the JAK-STAT pathway in a manner similar to that associated with JAK2 mutations. These results indicate that mutant CALR causes myeloproliferation because of the activation of JAK-STAT pathway and not by the inhibition of phagocytosis, which is similar to the myeloproliferation caused by JAK2 V617F mutation.
在许多携带非突变型Janus激酶2（JAK2）的原发性血小板增多症（ET）或原发性骨髓纤维化病例中，已观察到钙网蛋白（CALR）的体细胞突变。CALR主要定位于内质网腔，但在整个CALR库中，有一小部分分布在细胞表面。已知细胞表面的CALR可将促吞噬的“吃我”信号传导至巨噬细胞，并作为巨噬细胞吞噬作用的重要调节因子之一。在本研究中，我们试图阐明突变型CALR是否会影响巨噬细胞吞噬的阈值，并在CALR突变型ET的发病机制中发挥不可或缺的作用。首先，我们比较了骨髓增殖性肿瘤患者造血干细胞和祖细胞（HSPC）以及成熟血细胞上CALR的表面表达水平，发现突变型CALR的表面表达没有变化。接下来，我们比较了每个HSPC组分和成熟血细胞的巨噬细胞吞噬阈值，发现巨噬细胞吞噬效率没有显著变化。我们的数据表明，CALR突变不会影响巨噬细胞对吞噬作用的敏感性。最后，我们分析了ET患者每个HSPC水平上JAK2下游分子的磷酸化状态，发现CALR突变以与JAK2突变相关的类似方式激活了JAK-STAT通路。这些结果表明，突变型CALR导致骨髓增殖是由于JAK-STAT通路的激活，而非通过抑制吞噬作用，这与JAK2 V617F突变引起的骨髓增殖相似。
