Lysophosphatidic acid reverses Temsirolimus-induced changes in lipid droplets and mitochondrial networks in renal cancer cells

The Emerging Role of LPA as an Oncometabolite

Lysophosphatidic acid (LPA) is a phospholipid that displays potent signalling activities that are regulated in both an autocrine and paracrine manner. It can be found both extra- and intracellularly, where it interacts with different receptors to activate signalling pathways that regulate a plethora of cellular processes, including mitosis, proliferation and migration. LPA metabolism is complex, and its biosynthesis and catabolism are under tight control to ensure proper LPA levels in the body. In cancer patient specimens, LPA levels are frequently higher compared to those of healthy individuals and often correlate with poor responses and more aggressive disease. Accordingly, LPA, through promoting cancer cell migration and invasion, enhances the metastasis and dissemination of tumour cells. In this review, we summarise the role of LPA in the regulation of critical aspects of tumour biology and further discuss the available pre-clinical and clinical evidence regarding the feasibility and efficacy of targeting LPA metabolism for effective anticancer therapy.

Deregulated expression of the 14q32 miRNA cluster in clear cell renal cancer cells

Clear cell renal cell carcinomas (ccRCC) are characterized by arm-wide chromosomal alterations. Loss at 14q is associated with disease aggressiveness in ccRCC, which responds poorly to chemotherapeutics. The 14q locus contains one of the largest miRNA clusters in the human genome; however, little is known about the contribution of these miRNAs to ccRCC pathogenesis. In this regard, we investigated the expression pattern of selected miRNAs at the 14q32 locus in TCGA kidney tumors and in ccRCC cell lines. We demonstrated that the miRNA cluster is downregulated in ccRCC (and cell lines) as well as in papillary kidney tumors relative to normal kidney tissues (and primary renal proximal tubule epithelial (RPTEC) cells). We demonstrated that agents modulating expression of DNMT1 (e.g., 5-Aza-deoxycytidine) could modulate 14q32 miRNA expression in ccRCC cell lines. Lysophosphatidic acid (LPA, a lysophospholipid mediator elevated in ccRCC) not only increased labile iron content but also modulated expression of a 14q32 miRNA. Through an overexpression approach targeting a subset of 14q32 miRNAs (specifically at subcluster A: miR-431-5p, miR-432-5p, miR-127-3p, and miR-433-3p) in 769-P cells, we uncovered changes in cellular viability and claudin-1, a tight junction marker. A global proteomic approach was implemented using these miRNA overexpressing cell lines which uncovered ATXN2 as a highly downregulated target. Collectively, these findings support a contribution of miRNAs at 14q32 in ccRCC pathogenesis.

Inhibitory Effect of Ursolic Acid on Proliferation and Migration of Renal Carcinoma Cells and Its Mechanism

Background

Renal carcinoma is one of the most common malignant tumors in the urinary system. Autophagy can be both activated and inhibited in renal carcinoma, and it plays a double-edged role in the development of renal carcinoma. In the early stage of cancer, autophagy can suppress tumors. In the late stage, autophagy contributes to the survival of tumor cells in an unfavorable environment, and some autophagy-related proteins P62, LC3B, and beclin-1 have become indicators of the prognosis of patients with renal carcinoma.

Aim

To demonstrate that ursolic acid activates autophagy in renal carcinoma 786-O cells by inhibiting the hedgehog signaling pathway.

Methods

The effect of ursolic acid on the viability of 786-O cells was determined by the MTT method; the effect of ursolic acid on the proliferation and migration of 786-O cells was examined by crystalline violet staining and scratch assay, respectively. For the study of autophagy, we firstly screened the time points. Western blot assay was used to detect the expression level of autophagic protein P62 at different time points of ursolic acid on 786-O. Then, the Cell MeterTM Autophagy Assay Kit was used to detect the effect of different doses of ursolic acid on the autophagic fluorescence intensity of 786-O cells; the Western blot method was used to detect the effect of different doses of ursolic acid on the expression levels of LC3II and P62 proteins in 786-O cells. Further, AdPlus-mCherry-GFP-LC3B adenovirus transfection was used to detect the effect of ursolic acid on the autophagic flow of 786-O cells; ursolic acid was combined with the autophagy inhibitor chloroquine (CQ) to detect the expression level of autophagy protein LC3II by Western blot. In terms of mechanism, the effect of ursolic acid on hedgehog signaling pathway-related proteins in 786-O cells was detected by Western blot.

Results

Ursolic acid inhibited the activity, proliferation, and migration of 786-O cells, enhanced the fluorescence intensity of autophagosomes in 786-O cells, increased the expression level of autophagy marker protein LC3II, and inhibited the expression level of P62 in a time and dose-dependent manner; ursolic acid activated the autophagic flow in 786-O cells, which showed that ursolic acid caused the accumulation of autophagic fluorescent spots and enhanced the fluorescence intensity of autophagosomes. Ursolic acid activated the autophagic flow in 786-O cells, as evidenced by the accumulation of autophagic fluorescent spots and enhanced fluorescence intensity of autophagosomes, and the combined use of the autophagy inhibitor CQ increased the expression level of LC3II compared to ursolic acid alone; ursolic acid decreased the expression levels of PTCH1, GLI1, SMO, SHH, and c-Myc and increased the expression level of Sufu in the hedgehog signaling pathway.

Conclusion

Ursolic acid activates autophagy in renal carcinoma 786-O cells, probably by inhibiting hedgehog signaling pathway activity.

Molecular Characterization, Tumor Microenvironment Association, and Drug Susceptibility of DNA Methylation-Driven Genes in Renal Cell Carcinoma

Accumulating evidence suggests that DNA methylation has essential roles in the development of renal cell carcinoma (RCC). Aberrant DNA methylation acts as a vital role in RCC progression through regulating the gene expression, yet little is known about the role of methylation and its association with prognosis in RCC. The purpose of this study is to explore the DNA methylation-driven genes for establishing prognostic-related molecular clusters and providing a basis for survival prediction. In this study, 5,198 differentially expressed genes (DEGs) and 270 DNA methylation-driven genes were selected to obtain 146 differentially expressed DNA methylation-driven genes (DEMDGs). Two clusters were distinguished by consensus clustering using 146 DEMDGs. We further evaluated the immune status of two clusters and selected 106 DEGs in cluster 1. Cluster-based immune status analysis and functional enrichment analysis of 106 DEGs provide new insights for the development of RCC. To predict the prognosis of patients with RCC, a prognostic model based on eight DEMDGs was constructed. The patients were divided into high-risk groups and low-risk groups based on their risk scores. The predictive nomogram and the web-based survival rate calculator (http://127.0.0.1:3496) were built to validate the predictive accuracy of the prognostic model. Gene set enrichment analysis was performed to annotate the signaling pathways in which the genes are enriched. The correlation of the risk score with clinical features, immune status, and drug susceptibility was also evaluated. These results suggested that the prognostic model might be a promising prognostic tool for RCC and might facilitate the management of patients with RCC.

Protection of Quiescence and Longevity of IgG Memory B Cells by Mitochondrial Autophagy

The development of long-lived immune memory cells against pathogens is critical for the success of vaccines to establish protection against future infections. However, the mechanisms governing the long-term survival of immune memory cells remain to be elucidated. In this article, we show that the maintenance mitochondrial homeostasis by autophagy is critical for restricting metabolic functions to protect IgG memory B cell survival. Knockout of mitochondrial autophagy genes, Nix and Bnip3, leads to mitochondrial accumulation and increases in oxidative phosphorylation and fatty acid synthesis, resulting in the loss of IgG⁺ memory B cells in mice. Inhibiting fatty acid synthesis or silencing necroptosis gene Ripk3 rescued Nix^-/-Bnip3^-/- IgG memory B cells, indicating that mitochondrial autophagy is important for limiting metabolic functions to prevent cell death. Our results suggest a critical role for mitochondrial autophagy in the maintenance of immunological memory by protecting the metabolic quiescence and longevity of memory B cells.

Lysophosphatidic Acid Signaling in Cancer Cells: What Makes LPA So Special?

Lysophosphatidic acid (LPA) refers to a family of simple phospholipids that act as ligands for G protein-coupled receptors. While LPA exerts effects throughout the body in normal physiological circumstances, its pathological role in cancer is of great interest from a therapeutic viewpoint. The numerous LPA receptors (LPARs) are coupled to a variety of G proteins, and more than one LPAR is typically expressed on any given cell. While the individual receptors signal through conventional GPCR pathways, LPA is particularly efficacious in stimulating cancer cell proliferation and migration. This review addresses the mechanistic aspects underlying these pro-tumorigenic effects. We provide examples of LPA signaling responses in various types of cancers, with an emphasis on those where roles have been identified for specific LPARs. While providing an overview of LPAR signaling, these examples also reveal gaps in our knowledge regarding the mechanisms of LPA action at the receptor level. The current understanding of the LPAR structure and the roles of LPAR interactions with other receptors are discussed. Overall, LPARs provide insight into the potential molecular mechanisms that underlie the ability of individual GPCRs (or combinations of GPCRs) to elicit a unique spectrum of responses from their agonist ligands. Further knowledge of these mechanisms will inform drug discovery, since GPCRs are promising therapeutic targets for cancer.