Acidosis-induced regulation of adipocyte G0S2 promotes crosstalk between adipocytes and breast cancer cells as well as tumor progression

Bidirectional interactions between cancer cells and their microenvironment govern tumor progression. Among the stromal cells in this microenvironment, adipocytes have been reported to upregulate cancer cell migration and invasion by producing fatty acids. Conversely, cancer cells alter adipocyte phenotype notably via increased lipolysis. We aimed to identify the mechanisms through which cancer cells trigger adipocyte lipolysis and evaluate the functional consequences on cancer progression. Here, we show that cancer cell-induced acidification of the extracellular medium strongly promotes preadipocyte lipolysis through a mechanism that does not involve lipophagy but requires adipose triglyceride lipase (ATGL) activity. This increased lipolysis is triggered mainly by attenuation of the G0/G1 switch gene 2 (G0S2)-induced inhibition of ATGL. G0S2-mediated regulation in preadipocytes affects their communication with breast cancer cells, modifying the phenotype of the cancer cells and increasing their resistance to chemotherapeutic agents in vitro. Furthermore, we demonstrate that the adipocyte-specific overexpression of G0S2 impairs mammary tumor growth and lung metastasis formation in vivo. Our results highlight the importance of acidosis in cancer cell-adipocyte crosstalk and identify G0S2 as the main regulator of cancer-induced lipolysis, regulating tumor establishment and spreading.

Loss of G0/G1 switch gene 2 (G0S2) promotes disease progression and drug resistance in chronic myeloid leukaemia (CML) by disrupting glycerophospholipid metabolism

Tyrosine kinase inhibitors (TKIs) targeting BCR::ABL1 have turned chronic myeloid leukaemia (CML) from a fatal disease into a manageable condition for most patients. Despite improved survival, targeting drug-resistant leukaemia stem cells (LSCs) remains a challenge for curative CML therapy. Aberrant lipid metabolism can have a large impact on membrane dynamics, cell survival and therapeutic responses in cancer. While ceramide and sphingolipid levels were previously correlated with TKI response in CML, the role of lipid metabolism in TKI resistance is not well understood. We have identified downregulation of a critical regulator of lipid metabolism, G0/G1 switch gene 2 (G0S2), in multiple scenarios of TKI resistance, including (1) BCR::ABL1 kinase-independent TKI resistance, (2) progression of CML from the chronic to the blast phase of the disease, and (3) in CML versus normal myeloid progenitors. Accordingly, CML patients with low G0S2 expression levels had a worse overall survival. G0S2 downregulation in CML was not a result of promoter hypermethylation or BCR::ABL1 kinase activity, but was rather due to transcriptional repression by MYC. Using CML cell lines, patient samples and G0s2 knockout (G0s2-/- ) mice, we demonstrate a tumour suppressor role for G0S2 in CML and TKI resistance. Our data suggest that reduced G0S2 protein expression in CML disrupts glycerophospholipid metabolism, correlating with a block of differentiation that renders CML cells resistant to therapy. Altogether, our data unravel a new role for G0S2 in regulating myeloid differentiation and TKI response in CML, and suggest that restoring G0S2 may have clinical utility.

G0S2 ameliorates oxidized low-density lipoprotein-induced vascular endothelial cell injury by regulating mitochondrial apoptosis

Background

Oxidative low-density lipoprotein (ox-LDL)-induced endothelial cell damage is a major risk factor for atherosclerosis and its related cardiovascular diseases. The G0/G1 switch gene 2 (G0S2) is a multifunctional protein which has been poorly studied in atherosclerosis.

Methods

In this study, ox-LDL was utilized to construct a human aortic endothelial cell (HAEC) injury model.

Results

It was found that ox-LDL impaired cell viability, augmented lactate dehydrogenase (LDH) release, and reduced G0S2 levels in HAECs in a dose-dependent manner. Further, G0S2 overexpression improved the viability and restrained apoptosis of HAECs treated by ox-LDL. Conversely, G0S2 depletion decreased the viability and aggravated apoptosis of HAECs treated by ox-LDL. At the molecular level, G0S2 overexpression significantly increased the secretion of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPH-Px), promoted intracellular reactive oxygen species (ROS) production and malondialdehyde (MDA) content in HAECs under either normal or ox-LDL conditions. Meanwhile, the ox-LDL-induced mitochondrial dysfunction, as demonstrated by decreased mitochondrial membrane potential, translocation of mitochondrial cytochrome c (Cyt-c) to the cytoplasm, and activation of caspase-3 and caspase-9, was significantly reversed by G0S2 overexpression. In addition, G0S2 overexpression promoted the activation of AMP-activated protein kinase (AMPK) and increased the expression of nuclear factor erythroid-2-related factor-2 (Nrf2), sirtuin 1 (SIRT1) and heme oxygenase 1 (HO-1) under normal and ox-LDL conditions.

Conclusions

This study demonstrated that G0S2 protects against ox-LDL-induced vascular endothelial cell injury by regulating oxidative damage and mitochondrial homeostasis and may be a promising target for the treatment of atherosclerosis.

Lipolytic inhibitor G0S2 modulates glioma stem-like cell radiation response

BACKGROUND

Ionizing radiation (IR) therapy is the standard first-line treatment for newly diagnosed patients with glioblastoma (GBM), the most common and malignant primary brain tumor. However, the effects of IR are limited due to the aberrant radioresistance of GBM.

METHODS

Transcriptome analysis was performed using RNA-seq in radioresistant patient-derived glioma stem-like cells (GSCs). Survival of glioma patient and mice bearing-brain tumors was analyzed by Kaplan-Meier survival analysis. Lipid droplet and γ-H2AX foci-positive cells were evaluated using immunofluorescence staining.

RESULTS

Lipolytic inhibitor G0/G1 switch gene 2 (G0S2) is upregulated in radioresistant GSCs and elevated in clinical GBM. GBM patients with high G0S2 expression had significantly shorter overall survival compared with those with low expression of G0S2. Using genetic approaches targeting G0S2 in glioma cells and GSCs, we found that knockdown of G0S2 promoted lipid droplet turnover, inhibited GSC radioresistance, and extended survival of xenograft tumor mice with or without IR. In contrast, overexpression of G0S2 promoted glioma cell radiation resistance. Mechanistically, high expression of G0S2 reduced lipid droplet turnover and thereby attenuated E3 ligase RNF168-mediated 53BP1 ubiquitination through activated the mechanistic target of rapamycin (mTOR)-ribosomal S6 kinase (S6K) signaling and increased 53BP1 protein stability in response to IR, leading to enhanced DNA repair and glioma radioresistance.

CONCLUSIONS

Our findings uncover a new function for lipolytic inhibitor G0S2 as an important regulator for GSC radioresistance, suggesting G0S2 as a potential therapeutic target for treating gliomas.

G0S2a1 (G0/G1 switch gene 2a1) is downregulated by TNF-α in grass carp (Ctenopharyngodon idellus) hepatocytes through PPARα inhibition

G0/G1 switch gene 2 plays an important role in the regulation of lipolysis in mammals, but little is known about its gene (G0S2) structure and function in fish. In the present study, two genes, G0S2a and G0S2b were isolated and characterized from grass carp Ctenopharyngodon idella, which encode peptides of 111 and 84 amino acids, respectively. Moreover, alternative multiple exon usage resulted in a significant variation in the 5'-region of G0S2a transcripts yielding two isoforms (G0S2a1 and G0S2a2). Phylogenetic and synteny analyses indicated that G0S2a and G0S2b could have originated from the teleost-specific genome duplication event. Analysis of the exon-intron structures clarified that G0S2a contained an extra intron compared with G0S2b. G0S2a1, G0S2a2 and G0S2b mRNAs were highly expressed in adipose tissue and liver. G0S2a was localized to the cytoplasm and nucleus, while G0S2b was mainly localized in cytoplasm, suggesting that G0S2a and G0S2b may have different functions in grass carp. PPARα agonist caused an increase in G0S2a1 and G0S2b expression, revealing that they are subject to transcriptional control by PPARα-mediated signals. TNF-α treatment decreased G0S2a1 and G0S2a2 transcripts that paralleled TNF-α downregulation of PPARα; however, only the effects of TNF-α on G0S2a1 were attenuated by treatment with PPARα agonist. Our findings identify G0S2a, not G0S2b, as a target gene for TNF-α and reveal that TNF-α suppresses G0S2a1 gene expression through a PPARα-dependent pathway in grass carp hepatocytes.

Tissue expression pattern and polymorphism of G0S2 gene in porcine

Adipose triglyceride lipase (ATGL), catalyzing the initial step of hydrolysis of triacylglycerol (TAG) in adipocytes, has been known to be inhibited by G0/G1 switch protein 2 (G0S2). In this study, we determined tissue expression pattern and polymorphism of G0S2 gene in porcine. The results showed that the G0S2 transcript levels were very high in the liver and, to a lesser degree, in adipose tissues of greater omentum and suet fat; and low G0S2 transcript levels were observed in other tissues. A comparative study on the transcript levels between ATGL and G0S2 genes showed that ATGL transcript levels were high in all six adipose tissues, but negligible in the liver. Higher transcript levels were obtained for sows in adipose tissues of the inner layer of subcutaneous fat and suet fat, but higher expression values were found for boars in the liver, spleen, and stomach. 19 single nucleotide polymorphisms (SNPs), including 4 nonsynonymous SNPs (g.-307A>T, g.-394C>G, g.-565G>A, and g.-566T>C), were found in porcine G0S2 genomic DNA. Association analyses showed that the g.-565G>A and g.-742T>A SNPs were associated with back fat thickness (BFT). In conclusion, G0S2 mRNAs are abundantly expressed in porcine liver and adipose tissues of greater omentum and suet fat, and sex affects porcine G0S2 tissue transcript levels; meanwhile, the genetic diversity of porcine G0S2 gene is abundant and 2 SNPs are a genetic factor affecting BFT.