Context-dependent roles for autophagy in myeloid cells in tumor progression [Atg5_Pymt]

Autophagy is known to suppress tumor initiation by removing genotoxic stresses in normal cells. Conversely, autophagy is also known to support tumor progression by alleviating metabolic stresses in neoplastic cells. Centered on this pro-tumor role of autophagy, there have been many clinical trials to treat cancers through systemic blocking of autophagy. Such systemic inhibition affects both tumor cells and non-tumor cells, and the consequence of blocked autophagy in non-tumor cells in the context of tumor microenvironment is relatively understudied. Here, we examined the effect of autophagy-deficient myeloid cells on the progression of autophagy-competent tumors. We found that blocking autophagy only in myeloid cells modulated tumor progression markedly but such effects were context dependent. In a tumor implantation model, the growth of implanted tumor cells was substantially reduced in mice with autophagy-deficient myeloid cells; T cells infiltrated deeper into the tumors and were responsible for the reduced growth of the implanted tumor cells. In an oncogene-driven tumor induction model, however, tumors grew faster and metastasized more in mice with autophagy-deficient myeloid cells. These data demonstrate that the autophagy status of myeloid cells plays a critical role in tumor progression, promoting or suppressing tumor growth depending on the context of tumor-myeloid cell interactions. This study indicates that systemic use of autophagy inhibitors in cancer therapy may have differential effects on rates of tumor progression in patients due to effects on myeloid cells and that this warrants more targeted use of selective autophagy inhibitors in a cancer therapy in a clinical setting. Overall design: Gene expression from Atg5 WT Tumor associated macrophages (TAMs) and Atg5 KO TAMs were analyzed by RNA-seq. PyMT tumor tissues were harvested from Atg5 WT (MMTV-PyMT + Atg5flox/flox) and Atg5 KO (MMTV-PyMT + Atg5flox/flox+LysMcre) female mice in FVB/NJ background at 65 days of age. TAMs, CD11b+ F4/80+ Ly6G- Ly6C-, were isolated by FACS from the tumor tissues.

已知细胞自噬（autophagy）可通过清除正常细胞内的遗传毒性应激，抑制肿瘤起始发生。反之，细胞自噬亦可通过缓解肿瘤细胞的代谢应激，促进肿瘤进展。鉴于细胞自噬的这一促肿瘤功能，已有多项通过系统性阻断自噬治疗癌症的临床试验。此类系统性抑制会同时作用于肿瘤细胞与非肿瘤细胞，但肿瘤微环境背景下，非肿瘤细胞自噬被阻断后的相关效应仍相对缺乏研究。
本研究聚焦自噬缺陷型髓系细胞对自噬功能完整的肿瘤进展的影响。我们发现，仅阻断髓系细胞的自噬可显著调控肿瘤进展，但该效应具有情境依赖性。在肿瘤移植模型中，髓系细胞自噬缺陷的小鼠体内，移植肿瘤细胞的生长显著受抑；此时T细胞可更深浸润至肿瘤实质内，这是移植肿瘤生长受抑的关键原因。而在癌基因驱动的肿瘤诱导模型中，髓系细胞自噬缺陷的小鼠体内，肿瘤生长速度更快且转移程度更高。
上述数据表明，髓系细胞的自噬状态在肿瘤进展中发挥关键作用，其可根据肿瘤-髓系细胞互作的具体情境，分别促进或抑制肿瘤生长。本研究提示，癌症治疗中系统性使用自噬抑制剂，可能通过影响髓系细胞而对患者的肿瘤进展速率产生差异化影响，因此临床场景中需更针对性地应用选择性自噬抑制剂。
整体实验设计：通过RNA测序（RNA-seq）分析野生型Atg5（Atg5 WT）肿瘤相关巨噬细胞（tumor associated macrophages, TAMs）与敲除型Atg5（Atg5 KO TAMs）的基因表达。于65日龄的FVB/NJ背景雌性小鼠中，分别采集野生型Atg5（MMTV-PyMT + Atg5flox/flox）与敲除型Atg5（MMTV-PyMT + Atg5flox/flox+LysMcre）小鼠的PyMT肿瘤组织。通过荧光激活细胞分选术（FACS）从肿瘤组织中分离出CD11b+ F4/80+ Ly6G- Ly6C-表型的TAMs。