Genetic Screen for Cell Fitness in High or Low Oxygen Highlights Mitochondrial and Lipid Metabolism.

Human cells are able to sense and adapt to variations in oxygen levels. Historically, much research in this field has focused on hypoxia-inducible factor (HIF) signaling and reactive oxygen species (ROS). Here, we perform genome-wide CRISPR growth screens at 21%, 5%, and 1% oxygen to systematically identify gene knockouts with relative fitness defects in high oxygen (213 genes) or low oxygen (109 genes), most without known connection to HIF or ROS. Knockouts of many mitochondrial pathways thought to be essential, including complex I and enzymes in Fe-S biosynthesis, grow relatively well at low oxygen and thus are buffered by hypoxia. In contrast, in certain cell types, knockout of lipid biosynthetic and peroxisomal genes causes fitness defects only in low oxygen. Our resource nominates genetic diseases whose severity may be modulated by oxygen and links hundreds of genes to oxygen homeostasis.

TMEM189 as a target gene of MiR-499a-5p regulates breast cancer progression through the ferroptosis pathway.

MicroRNA (miR)-499a-5p has been reported to regulate the progression of various tumours. However, the role of miR-499a-5p in breast cancer is unclear. The purpose of this study was to investigate the role and mechanism of miR-499a-5p in breast cancer. The growth effect of miR-499a-5p on breast cancer cells was investigated by the CCK-8 assay, wound healing assay and Transwell invasion assay. The luciferase activity assay was used to verify the downstream targets of miR-499a-5p. The levels of GSH, MDA, and ROS were detected by kits. Quantitative real-time PCR and Western blot were used to determine the expression levels of TMEM189, COX-2, GPX4, and other related genes in cells. miR-499a-5p was down-regulated in MDA-MB-231 cells and was shown to reduced the viability, migration and invasion of MDA-MB-231 cells. Further studies revealed that TMEM189 is a target of miR-499a-5p. miR-499a-5p inhibited breast cancer cell growth by downregulating TMEM189. Furthermore, the down-regulation of TMEM189 promotes ferroptosis in breast cancer cells. The low expression of TMEM189 inhibited the development of breast cancer through the ferroptosis pathway. We have demonstrated for the first time that miR-499a-5p inhibits breast cancer progression by targeting the TMEM189-mediated ferroptosis pathway.

TMEM189 promotes breast cancer through inhibition of autophagy-regulated ferroptosis.

Breast cancer is a leading cause of tumor-related death among women around the world, but its pathogenesis is still unclear. Transmembrane protein 189 (TMEM189) is widely expressed in many types of tissues and plays a critical role in tumorigenesis partly through mediating cell death. However, its regulatory function on breast cancer progression and particularly the underlying mechanisms have not been fully understood. In the present study, we found that TMEM189 knockdown significantly reduced the proliferation of breast cancer cells, while its over-expression facilitated the proliferative capacity of tumor cells. The effects of TMEM189 to promote breast cancer were validated in the constructed xenograft mouse models. RNA-sequencing studies subsequently showed that TMEM189 deletion was closely associated with ferroptosis signaling pathway, accompanied with elevated lipid reactive oxygen species (ROS) accumulation, cellular ROS production, malondialdehyde (MDA) and the intracellular iron releases. However, GSH levels in breast cancer cells were highly impeded upon TMEM189 inhibition. Intriguingly, we found that TMEM189 knockdown-induced ferroptotic cell death was considerably abolished after autophagy inhibitor 3-MA co-treatment, as evidenced by the markedly decreased ROS generation and intracellular iron accumulation. Moreover, TMEM189 ablation strongly up-regulated LC3BII and transferrin receptor 1 (TfR1) expression levels in breast cancer cells, whereas down-regulated p62 and GPX4. Importantly, the expression changes of these molecules related to autophagy and ferroptosis were almost diminished in response to 3-MA exposure, along with restored cell proliferation. These findings suggested that TMEM189 could inhibit autophagy to mediate ferroptosis in breast cancer cells. Collectively, all our findings revealed the therapeutic potential of TMEM189 in the treatment of breast cancer.

The presence of plasmenyl ether lipids in Capsaspora owczarzaki suggests a premetazoan origin of plasmalogen biosynthesis in animals.

Plasmalogens are glycerophospholipids with a vinyl ether bond, rather than an ester bond, at sn-1 position. These lipids were described in anaerobic bacteria, myxobacteria, animals and some protists, but not in plants or fungi. Anaerobic and aerobic organisms synthesize plasmalogens differently. The aerobic pathway requires oxygen in the last step, which is catalyzed by PEDS1. CarF and TMEM189 were recently identified as the PEDS1 from myxobacteria and mammals, which could be of valuable use in exploring the distribution of this pathway in eukaryotes. We show the presence of plasmalogens in Capsaspora owczarzaki, one of the closest unicellular relatives of animals. This is the first report of plasmalogens in non-metazoan opisthokontas. Analysis of its genome revealed the presence of enzymes of the aerobic pathway. In a broad BLAST search, we found PEDS1 homologs in Opisthokonta and some genera of Amoebozoa and Excavata, consistent with the restricted distribution of plasmalogens reported in eukaryotes. Within Opisthokonta, PEDS1 is limited to Filasterea (Capsaspora and Pigoraptor), Metazoa and a small group of fungi comprising three genera of ascomycetes. A phylogenetic analysis of PEDS1 traced the acquisition of plasmalogen synthesis in animals to a filasterean ancestor and suggested independent acquisition events for Amoebozoa, Excavata and Ascomycetes.

Decoding the Expressions, Immune Relevance, and Prognostic Values of Ferroptosis Gene TMEM189: A Pan-Cancer Analysis.

BACKGROUND: TMEM189 is a recently discovered transmembrane protein involved in ether glycerophospholipid synthesis and ferroptosis regulation. However, its role in tumors are not well understood. OBJECTIVE: To elucidate the oncogenic effects and prognostic values of TMEM189 in tumors. METHODS: We performed a pan-cancer analysis of TMEM189 using various databases, bioinformatics and statistical tools, and tissue microarray analysis. RESULTS: TMEM189 is generally upregulated in tumors compared to normal tissues. High TMEM189 expression is linked to reduced promoter methylation. TMEM189 exhibits a negative correlation with immunogenic markers, immune cell infiltration, and expression of immune checkpoint genes (ICGs) in most cancers, implicating its immunosuppressive role in tumor microenvironments (TME). The interacting and similar genes with TMEM189 were involved in hotspot signaling pathways in pan-cancer. TMEM189 overexpression is usually associated with poor prognosis, especially an independent prognostic risk factor for BLCA, BRCA, LUAD, MESO, LIHC and SKCM. CONCLUSION: TMEM189 is overexpressed and exerts immunosuppressive effects in many tumors with a significant association with poor prognosis, suggesting its potential as a therapeutic target in cancer treatment.

Plasmalogens and Photooxidative Stress Signaling in Myxobacteria, and How it Unmasked CarF/TMEM189 as the Δ1'-Desaturase PEDS1 for Human Plasmalogen Biosynthesis.

Plasmalogens are glycerophospholipids with a hallmark sn-1 vinyl ether bond that endows them with unique physical-chemical properties. They have proposed biological roles in membrane organization, fluidity, signaling, and antioxidative functions, and abnormal plasmalogen levels correlate with various human pathologies, including cancer and Alzheimer's disease. The presence of plasmalogens in animals and in anaerobic bacteria, but not in plants and fungi, is well-documented. However, their occurrence in the obligately aerobic myxobacteria, exceptional among aerobic bacteria, is often overlooked. Tellingly, discovery of the key desaturase indispensable for vinyl ether bond formation, and therefore fundamental in plasmalogen biogenesis, emerged from delving into how the soil myxobacterium Myxococcus xanthus responds to light. A recent pioneering study unmasked myxobacterial CarF and its human ortholog TMEM189 as the long-sought plasmanylethanolamine desaturase (PEDS1), thus opening a crucial door to study plasmalogen biogenesis, functions, and roles in disease. The findings demonstrated the broad evolutionary sweep of the enzyme and also firmly established a specific signaling role for plasmalogens in a photooxidative stress response. Here, we will recount our take on this fascinating story and its implications, and review the current state of knowledge on plasmalogens, their biosynthesis and functions in the aerobic myxobacteria.

Ether phospholipids govern ferroptosis.

Ferroptosis is a cell death modality triggered by excessive lipid peroxidation. Two recent studies (Zou et al., 2020; Cui et al., 2021) not only reveal critical roles of ether-linked phospholipids as an additional source for providing polyunsaturated fatty acid-containing phospholipids in driving ferroptosis but also suggest a context-dependent role of TMEM189-mediated vinyl-ether phospholipid (plasmalogen) synthesis in ferroptosis.