Grasso Carole, Eccles David A, Boukalova Stepana, Fabre Marie-Sophie, Dawson Rebecca H, Neuzil Jiri, Herst Patries M, Berridge Michael V
Malaghan Institute of Medical Research, Wellington, New Zealand.
Institute of Biotechnology, Czech Academy of Sciences, Vestec, Czechia.
Front Physiol. 2020 Nov 24;11:543962. doi: 10.3389/fphys.2020.543962. eCollection 2020.
Tumor cells without mitochondrial (mt) DNA (ρ cells) are auxotrophic for uridine, and their growth is supported by pyruvate. While ATP synthesis in ρ cells relies on glycolysis, they fail to form tumors unless they acquire mitochondria from stromal cells. Mitochondrial acquisition restores respiration that is essential for pyrimidine biosynthesis and for mitochondrial ATP production. The physiological processes that underpin intercellular mitochondrial transfer to tumor cells lacking mtDNA and the metabolic remodeling and restored tumorigenic properties of cells that acquire mitochondria are not well understood. Here, we investigated the changes in mitochondrial and nuclear gene expression that accompany mtDNA deletion and acquisition in metastatic murine 4T1 breast cancer cells. Loss of mitochondrial gene expression in 4T1ρ cells was restored in cells recovered from subcutaneous tumors that grew from 4T1ρ cells following acquisition of mtDNA from host cells. In contrast, the expression of most nuclear genes that encode respiratory complex subunits and mitochondrial ribosomal subunits was not greatly affected by loss of mtDNA, indicating ineffective mitochondria-to-nucleus communication systems for these nuclear genes. Further, analysis of nuclear genes whose expression was compromised in 4T1ρ cells showed that immune- and stress-related genes were the most highly differentially expressed, representing over 70% of those with greater than 16-fold higher expression in 4T1 compared with 4T1ρ cells. The monocyte recruiting chemokine, Ccl2, and Psmb8, a subunit of the immunoproteasome that generates MHCI-binding peptides, were the most highly differentially expressed. Early monocyte/macrophage recruitment into the tumor mass was compromised in 4T1ρ cells but recovered before mtDNA could be detected. Taken together, our results show that mitochondrial acquisition by tumor cells without mtDNA results in bioenergetic remodeling and re-expression of genes involved in immune function and stress adaptation.
没有线粒体（mt）DNA的肿瘤细胞（ρ细胞）对尿苷是营养缺陷型的，其生长由丙酮酸支持。虽然ρ细胞中的ATP合成依赖糖酵解，但除非它们从基质细胞获得线粒体，否则无法形成肿瘤。线粒体的获得恢复了呼吸作用，这对嘧啶生物合成和线粒体ATP产生至关重要。细胞间线粒体转移到缺乏mtDNA的肿瘤细胞以及获得线粒体的细胞的代谢重塑和恢复的致瘤特性所依据的生理过程尚不清楚。在这里，我们研究了转移性小鼠4T1乳腺癌细胞中线粒体和核基因表达随mtDNA缺失和获得的变化。从皮下肿瘤中恢复的细胞中，4T1ρ细胞中线粒体基因表达的缺失在从宿主细胞获得mtDNA后从4T1ρ细胞生长而来的皮下肿瘤中得到恢复。相比之下，大多数编码呼吸复合物亚基和线粒体核糖体亚基核基因的表达并未受到mtDNA缺失的显著影响，这表明这些核基因的线粒体到细胞核的通讯系统效率低下。此外，对在4T1ρ细胞中表达受损的核基因的分析表明，免疫和应激相关基因的差异表达最为显著，占与4T1ρ细胞相比在4T1中表达高出16倍以上的基因的70%以上。单核细胞趋化因子Ccl2和参与产生MHC I结合肽的免疫蛋白酶体亚基Psmb8的差异表达最为显著。早期单核细胞/巨噬细胞募集到肿瘤块中在4T1ρ细胞中受损，但在检测到mtDNA之前恢复。总之，我们的结果表明，没有mtDNA的肿瘤细胞获得线粒体导致生物能量重塑以及参与免疫功能和应激适应的基因重新表达。
