Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710, USA.
Oncogene. 2011 Apr 21;30(16):1855-67. doi: 10.1038/onc.2010.561. Epub 2010 Dec 13.
Hematopoietic cells normally require cell extrinsic signals to maintain metabolism and survival. In contrast, cancer cells can express constitutively active oncogenic kinases such as BCR-Abl that promote these processes independent of extrinsic growth factors. When cells receive insufficient growth signals or when oncogenic kinases are inhibited, glucose metabolism decreases and the self-digestive process of autophagy is elevated to degrade bulk cytoplasm and organelles. Although autophagy has been proposed to provide a cell-intrinsic nutrient supply for mitochondrial oxidative metabolism and to maintain cellular homeostasis through degradation of damaged organelles or protein aggregates, its acute role in growth factor deprivation or inhibition of oncogenic kinases remains poorly understood. We therefore developed a growth factor-dependent hematopoietic cell culture model in which autophagy can be acutely disrupted through conditional Cre-mediated excision of the autophagy-essential gene Atg3. Treated cells rapidly lost their ability to perform autophagy and underwent cell cycle arrest and apoptosis. Although Atg3 was essential for optimal upregulation of mitochondrial oxidative pathways in growth factor withdrawal, this metabolic contribution of autophagy did not appear critical for cell survival, as provision of exogenous pyruvate or lipids could not completely rescue Atg3 deficiency. Instead, autophagy suppressed a stress response that otherwise led to p53 phosphorylation and upregulation of p21 and the pro-apoptotic Bcl-2 family protein Puma. Importantly, BCR-Abl-expressing cells had low basal levels of autophagy, but were highly dependent on this process, and rapidly underwent apoptosis upon disruption of autophagy through Atg3 deletion or treatment with chemical autophagy inhibitors. This dependence on autophagy extended in vivo, as Atg3 deletion also prevented BCR-Abl-mediated leukemogenesis in a cell transfer model. Together these data demonstrate a critical role for autophagy to mitigate cell stress, and that cells expressing the oncogenic kinase BCR-Abl appear particularly dependent on autophagy for cell survival and leukemogenesis.
造血细胞通常需要细胞外信号来维持代谢和存活。相比之下，癌细胞可以表达组成性激活的致癌激酶，如 BCR-Abl，这些激酶可以独立于细胞外生长因子促进这些过程。当细胞接收到不足的生长信号或致癌激酶被抑制时，葡萄糖代谢减少，自噬的自我消化过程被提升以降解细胞质和细胞器。尽管自噬被认为可以为线粒体氧化代谢提供细胞内营养供应，并通过降解受损的细胞器或蛋白质聚集体来维持细胞内稳态，但它在生长因子剥夺或抑制致癌激酶中的急性作用仍知之甚少。因此，我们开发了一种依赖生长因子的造血细胞培养模型，其中自噬可以通过条件性 Cre 介导的自噬必需基因 Atg3 的切除而被急性破坏。经处理的细胞迅速丧失进行自噬的能力，并经历细胞周期停滞和细胞凋亡。尽管 Atg3 对于生长因子撤出时最佳上调线粒体氧化途径至关重要，但自噬的这种代谢贡献对于细胞存活似乎并不关键，因为提供外源性丙酮酸或脂质并不能完全挽救 Atg3 缺陷。相反，自噬抑制了应激反应，否则会导致 p53 磷酸化和 p21 以及促凋亡 Bcl-2 家族蛋白 Puma 的上调。重要的是，表达 BCR-Abl 的细胞自噬水平较低，但对该过程高度依赖，并且通过 Atg3 缺失或用化学自噬抑制剂处理破坏自噬后迅速发生细胞凋亡。这种对自噬的依赖性在体内延伸，因为 Atg3 缺失也阻止了 BCR-Abl 介导的白血病发生在细胞转移模型中。这些数据共同表明自噬在减轻细胞应激方面起着关键作用，并且表达致癌激酶 BCR-Abl 的细胞似乎特别依赖自噬来维持细胞存活和白血病发生。
