Role of Autophagy in Cancer

描述（由申请人提供）：细胞通过大自噬（以下称为自噬）过程捕获细胞内蛋白质和细胞器，将其递送至溶酶体并在溶酶体中降解。自噬货物的分解产物如氨基酸、糖、核苷和脂质从溶酶体释放到细胞质中，在细胞质中它们被重新使用。自噬从而使细胞内组分活化以维持细胞和生物体的代谢和在饥饿中的存活，这是从酵母到哺乳动物保守的功能。自噬也是一种消除细胞废物的机制，例如受损的蛋白质和细胞器，特别是线粒体，其积累是有毒的。这种蛋白质和细胞器的自噬质量控制功能也是高度保守的，是稳态所必需的。自噬水平通常较低，但饥饿和应激会显著诱导自噬，以促进细胞适应。癌细胞也依赖自噬，但比正常细胞更依赖自噬。这可能是由于癌细胞生长和驻留在应激微环境中所施加的高代谢需求。与正常细胞相反，癌细胞通常在进食条件下诱导自噬。例如，Ras驱动的癌症通常具有高水平的基础自噬，并且极其依赖于自噬来维持线粒体呼吸、在压力下存活和肿瘤发生。因此，与正常细胞相比，一些癌症可能对自噬上瘾，并且优先对自噬抑制敏感，从而促进了对抑制自噬以改善癌症治疗的兴趣。自噬究竟如何支持癌症的生长和存活，正常组织和肿瘤受到不同影响的程度，以及最有效的手段是在临床上实施这一概念，仍然是悬而未决的问题。为了解决这些问题，我们使用基因工程小鼠模型（GEMM）研究了自噬在K-rasG 12 D驱动的非小细胞肺癌（NSCLC）和B-rafV 600 E驱动的肺癌中的作用。我们发现，缺乏必要的自噬基因atg 7会导致肿瘤细胞积累大量有缺陷的线粒体并发生萎缩。atg 7缺陷也使肺腺瘤和癌的进展转向嗜酸细胞瘤。嗜酸细胞瘤是一种罕见的良性肿瘤，主要发生在上皮组织中，其特征是大量呼吸缺陷的突变线粒体的积累。这一发现首次揭示了自噬是癌症命运的决定因素，自噬缺陷可能是嗜酸细胞瘤发生的分子基础，并且当自噬受损时，嗜酸细胞瘤可以源自腺瘤和癌。我们将检验自噬缺陷是嗜酸细胞瘤发生的分子基础这一中心假设。我们将确定atg 7缺陷是否产生线粒体基因组突变，将癌转化为嗜酸细胞瘤，如果在必要的自噬基因突变导致人类嗜酸细胞瘤，如果通过敲除自噬产生嗜酸细胞瘤产生对代谢应激的敏感性，增强癌症治疗。

DESCRIPTION (provided by applicant): Cells capture intracellular proteins and organelles by the process of macroautophagy (autophagy hereafter), which delivers them to lysosomes where they are degraded. The breakdown products of autophagy cargo such as amino acids, sugars, nucleosides and lipids, are released from lysosomes into the cytoplasm where they are reused. Autophagy thereby recycles intracellular components to sustain cell and organism metabolism and survival in starvation, a function conserved from yeast to mammals. Autophagy is also a mechanism for eliminating cellular waste such as damaged proteins and organelles, particularly mitochondria, the accumulation of which is toxic. This protein and organelle quality control function of autophagy is also highly conserved and required for homeostasis. Autophagy levels are normally low, but are dramatically induced by starvation and stress to facilitate cellular adaptation. Cancer cells also rely on autophagy, but more so than normal cells. This may be due to high metabolic demand imposed by cancer cell growth and residence in a stressful microenvironment. In contrast to normal cells, cancer cells often have autophagy induced under fed conditions. For example, Ras-driven cancers commonly have high levels of basal autophagy and are extremely dependent on autophagy for sustaining mitochondrial respiration, for survival in stress and for tumorigenesis. Thus, in comparison to normal cells, some cancers may be addicted to autophagy and preferentially sensitive to autophagy inhibition, prompting interest in inhibiting autophagy to improve cancer therapy. Precisely how autophagy supports cancer growth and survival, the extent to which normal tissues and tumors are differentially affected, and the most effective means is to implement this concept in the clinic, remain open questions. To address these questions we examined the role of autophagy using genetically engineered mouse models (GEMMs) for K-rasG12D-driven non-small-cell lung cancer (NSCLC) and B-rafV600E- driven lung cancer. We found that deficiency in the essential autophagy gene atg7 causes tumor cells to accumulate large numbers of defective mitochondria and undergo atrophy. Atg7 deficiency also diverts progression of lung adenomas and carcinomas to oncocytomas. Oncocytomas are rare, predominantly benign neoplasms that arise in epithelial tissues that are characterized by the accumulation of large numbers of respiration-defective, mutant mitochondria. This discovery revealed for the first time that autophagy is a cancer fate determinant, that autophagy defects may be the molecular basis for the genesis of oncocytomas, and that oncocytomas can derive from adenomas and carcinomas when autophagy is impaired. We will test the central hypothesis that autophagy defects are the molecular basis for the genesis of oncocytomas. We will determine if atg7 deficiency produces mitochondrial genome mutations that convert carcinomas to oncocytomas, if mutations in essential autophagy genes cause human oncocytomas, and if producing oncocytomas by knocking out autophagy creates sensitivity to metabolic stress, enhancing cancer therapy.