Human cancer cells display extensive heterogeneity in their sensitivities to the proteasome inhibitor bortezomib (Velcade). The molecular mechanisms underlying this heterogeneity remain unclear, and strategies to overcome resistance are limited. Here, we discover that inherent differences in eIF2α phosphorylation among a panel of ten human pancreatic cancer cell lines significantly impacts bortezomib sensitivity, and implicate the HRI (heme-regulated inhibitor) eIF2α kinase as a novel therapeutic target. Within our panel, we identified a subset of cell lines with defective induction of eIF2α phosphorylation, conferring a high degree of sensitivity to bortezomib. These bortezomib-sensitive cells exhibited impaired translation attenuation followed by toxic accumulation of protein aggregates and reactive oxygen species (ROS), whereas the bortezomib-resistant cell lines displayed increased phosphorylation of eIF2α, decreased translation, few protein aggregates, and minimal ROS production. Importantly, we identified HRI as the primary bortezomib-activated eIF2α kinase, and demonstrated that HRI knockdown promoted cell death in the bortezomib-resistant cells. Overall, our data implicate inducible HRI-mediated phosphorylation of eIF2α as a central cytoprotective mechanism following exposure to bortezomib and provide proof-of-concept for the development of HRI inhibitors to overcome proteasome inhibitor resistance.

中文翻译：

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HRI介导的翻译抑制可降低人胰腺癌细胞中的蛋白毒性和对硼替佐米的敏感性。

人类癌细胞对蛋白酶体抑制剂硼替佐米（Velcade）的敏感性表现出广泛的异质性。造成这种异质性的分子机制仍然不清楚，克服耐药性的策略也受到限制。在这里，我们发现一组十个人类胰腺癌细胞系之间的eIF2α磷酸化固有差异显着影响硼替佐米的敏感性，并暗示HRI（血红素调节抑制剂）eIF2α激酶是一种新型治疗靶点。在我们的小组中，我们鉴定了eIF2α磷酸化诱导缺陷的细胞系的一个子集，从而赋予了对硼替佐米的高度敏感性。这些对硼替佐米敏感的细胞表现出受损的翻译减弱，随后蛋白聚集体和活性氧（ROS）发生有毒积累，而耐硼替佐米的细胞系显示eIF2α的磷酸化增加，翻译减少，蛋白质聚集很少，ROS产生最少。重要的是，我们将HRI确定为主要的硼替佐米激活的eIF2α激酶，并证明HRI抑制可促进耐硼替佐米的细胞死亡。总体而言，我们的数据表明，在暴露于硼替佐米后，eIF2α的可诱导HRI介导的磷酸化是一个中心的细胞保护机制，并为开发HRI抑制剂克服蛋白酶体抑制剂的耐药性提供了概念验证。并证明了HRI抑制可促进耐硼替佐米的细胞死亡。总体而言，我们的数据表明，在与硼替佐米接触后，eIF2α的可诱导HRI介导的磷酸化是主要的细胞保护机制，并为开发HRI抑制剂克服蛋白酶体抑制剂耐药性提供了概念验证。并证明敲除HRI可以促进耐硼替佐米的细胞死亡。总体而言，我们的数据表明，在与硼替佐米接触后，eIF2α的可诱导HRI介导的磷酸化是主要的细胞保护机制，并为开发HRI抑制剂克服蛋白酶体抑制剂耐药性提供了概念验证。