多发性骨髓瘤(MM)是典型的蛋白酶体抑制剂(PI)反应性癌症,但是很多病人没有反应.增强敏感性的一个有吸引力的目标是(宏观)自噬,最近发现骨髓浆细胞是必需的,MM的正常对应物。这里,将蛋白质组学与假设驱动的策略相结合,我们鉴定了自噬货物受体和衔接蛋白,SQSTM1/p62作为自噬储备的重要组成部分,不仅与蛋白酶体协同作用,维持蛋白质的稳定,但也介导了对PI的可塑性适应性反应,并忠实地报告固有的PI灵敏度。慢病毒工程揭示SQSTM1对于MM细胞存活是必需的并且提供特异性PI保护。在基础条件下,SQSTM1依赖性自噬通过组成型处置大量泛素化蛋白来减轻蛋白酶体的降解负担。的确,它的抑制或刺激非常敏感,或受到保护,PI诱导的蛋白质聚集和细胞死亡。此外,在蛋白酶体应激下,骨髓瘤细胞选择性增强SQSTM1从头表达并重置其巨大的内源性相互作用组,从信号伙伴转移SQSTM1,以最大化其与泛素化蛋白的关联。这种自噬储备的饱和度,如未消化的SQSTM1阳性聚集体的细胞内积累所示,特异性区分患者来源的骨髓瘤,对PI固有易感,与主要耐药的骨髓瘤。这些聚集体与内质网的积累有关,其中比较蛋白质组学鉴定为MM中自噬靶向的主要细胞区室。总之,这些数据将自噬整合到我们先前建立的蛋白酶体负荷与容量模型中,并揭示SQSTM1聚集是蛋白质停滞缺陷的忠实标记,为MM定义了一个新的预后和治疗框架。
Multiple myeloma (MM) is the paradigmatic proteasome inhibitor (PI) responsive cancer, but many patients fail to respond. An attractive target to enhance sensitivity is (macro)autophagy, recently found essential to bone marrow plasma cells, the normal counterpart of MM. Here, integrating proteomics with hypothesis-driven strategies, we identified the autophagic cargo receptor and adapter protein, SQSTM1/p62 as an essential component of an autophagic reserve that not only synergizes with the proteasome to maintain proteostasis, but also mediates a plastic adaptive response to PIs, and faithfully reports on inherent PI sensitivity. Lentiviral engineering revealed that SQSTM1 is essential for MM cell survival and affords specific PI protection. Under basal conditions, SQSTM1-dependent autophagy alleviates the degradative burden on the proteasome by constitutively disposing of substantial amounts of ubiquitinated proteins. Indeed, its inhibition or stimulation greatly sensitized to, or protected from, PI-induced protein aggregation and cell death. Moreover, under proteasome stress, myeloma cells selectively enhanced SQSTM1 de novo expression and reset its vast endogenous interactome, diverting SQSTM1 from signaling partners to maximize its association with ubiquitinated proteins. Saturation of such autophagic reserve, as indicated by intracellular accumulation of undigested SQSTM1-positive aggregates, specifically discriminated patient-derived myelomas inherently susceptible to PIs from primarily resistant ones. These aggregates correlated with accumulation of the endoplasmic reticulum, which comparative proteomics identified as the main cell compartment targeted by autophagy in MM. Altogether, the data integrate autophagy into our previously established proteasome load-versus-capacity model, and reveal SQSTM1 aggregation as a faithful marker of defective proteostasis, defining a novel prognostic and therapeutic framework for MM.