Crosby J S, Chefalo P J, Yeh I, Ying S, London I M, Leboulch P, Chen J J
Harvard-Massachusetts Institute of Technology, Division of Health Sciences and Technology, Cambridge MA, USA.
Blood. 2000 Nov 1;96(9):3241-8.
Protein synthesis in reticulocytes depends on the availability of heme. In heme deficiency, inhibition of protein synthesis correlates with the activation of heme-regulated eIF-2alpha kinase (HRI), which blocks the initiation of protein synthesis by phosphorylating eIF-2alpha. HRI is a hemoprotein with 2 distinct heme-binding domains. Heme negatively regulates HRI activity by binding directly to HRI. To further study the physiological function of HRI, the wild-type (Wt) HRI and dominant-negative inactive mutants of HRI were expressed by retrovirus-mediated transfer in both non-erythroid NIH 3T3 and mouse erythroleukemic (MEL) cells. Expression of Wt HRI in 3T3 cells resulted in the inhibition of protein synthesis, a loss of proliferation, and eventually cell death. Expression of the inactive HRI mutants had no apparent effect on the growth characteristics or morphology of NIH 3T3 cells. In contrast, expression of 3 dominant-negative inactive mutants of HRI in MEL cells resulted in increased hemoglobin production and increased proliferative capacity of these cells upon dimethyl-sulfoxide induction of erythroid differentiation. These results directly demonstrate the importance of HRI in the regulation of protein synthesis in immature erythroid cells and suggest a role of HRI in the regulation of the numbers of matured erythroid cells.
网织红细胞中的蛋白质合成依赖于血红素的可用性。在血红素缺乏时，蛋白质合成的抑制与血红素调节的真核起始因子2α激酶（HRI）的激活相关，HRI通过磷酸化真核起始因子2α来阻断蛋白质合成的起始。HRI是一种具有2个不同血红素结合结构域的血红素蛋白。血红素通过直接与HRI结合来负向调节HRI活性。为了进一步研究HRI的生理功能，野生型（Wt）HRI和HRI的显性负性失活突变体通过逆转录病毒介导的转移在非红系NIH 3T3细胞和小鼠红白血病（MEL）细胞中表达。Wt HRI在3T3细胞中的表达导致蛋白质合成受到抑制、增殖丧失并最终导致细胞死亡。失活的HRI突变体的表达对NIH 3T3细胞的生长特性或形态没有明显影响。相反，HRI的3个显性负性失活突变体在MEL细胞中的表达导致在二甲基亚砜诱导红系分化后这些细胞的血红蛋白产量增加和增殖能力增强。这些结果直接证明了HRI在未成熟红系细胞蛋白质合成调节中的重要性，并提示HRI在成熟红系细胞数量调节中发挥作用。
