Lactate dehydrogenase A promotes nasopharyngeal carcinoma progression through the TAK1/NF-κB Axis.

BACKGROUND: Nasopharyngeal carcinoma (NPC) is a malignant tumor that originates in the nasopharyngeal mucosa and is common in China and Southeast Asian countries. Cancer cells reprogram glycolytic metabolism to promote their growth, survival and metastasis. Glycolysis plays an important role in NPC development, but the underlying mechanisms remain incompletely elucidated. Lactate dehydrogenase A (LDHA) is a crucial glycolytic enzyme, catalyzing the last step of glycolysis. This study aims to investigate the exact role of LDHA, which catalyzes the conversion of pyruvate into lactate, in NPC development. METHODS AND RESULTS: The western blot and immunohistochemical (IHC) results indicated that LDHA was significantly upregulated in NPC cells and clinical samples. LDHA knockdown by shRNA significantly inhibited NPC cell proliferation and invasion. Further knockdown of LDHA dramatically weakened the tumorigenicity of NPC cells in vivo. Mechanistic studies showed that LDHA activated TGF-ß-activated kinase 1 (TAK1) and subsequent nuclear factor κB (NF-κB) signaling to promote NPC cell proliferation and invasion. Exogenous lactate supplementation restored NPC cell proliferation and invasion inhibited by LDHA knockdown, and this restorative effect was reversed by NF-κB inhibitor (BAY 11-7082) or TAK1 inhibitor (5Z-7-oxozeaenol) treatment. Moreover, clinical sample analyses showed that LDHA expression was positively correlated with TAK1 Thr187 phosphorylation and poor prognosis. CONCLUSIONS: Our results suggest that LDHA and its major metabolite lactate drive NPC progression by regulating TAK1 and its downstream NF-κB signaling, which could become a therapeutic target in NPC.

GFAT1-linked TAB1 glutamylation sustains p38 MAPK activation and promotes lung cancer cell survival under glucose starvation.

Reprogrammed cell metabolism is deemed as one of the hallmarks of cancer. Hexosamine biosynthesis pathway (HBP) acts as an "energy sensor" in cells to regulate metabolic fluxes. Glutamine-fructose-6-phosphate amidotransferase 1 (GFAT1), the rate-limiting enzyme of HBP, is broadly found with elevated expression in human cancers though its exact and concrete role in tumorigenesis still remains unknown and needs further investigation. P38 mitogen-activated protein kinase (MAPK) is an important component of stress-signaling pathway and plays a critical role in cell fate decision, whereas the underlying mechanism of its activation under nutrient stress also remains elusive. In this study, we show that glucose deprivation induces the interaction of GFAT1 with transforming growth factor ß-activated kinase 1 binding protein 1 (TAB1) in a TAB1 S438 phosphorylation-dependent manner. Subsequently, the binding of GFAT1 to TAB1 facilitates TTLL5-GFAT1-TAB1 complex formation, and the metabolic activity of GFAT1 for glutamate production further contributes to TTLL5-mediated TAB1 glutamylation. In consequence, TAB1 glutamylation promotes the recruitment of p38α MAPK and thus drives p38 MAPK activation. Physiologically, GFAT1-TAB1-p38 signaling promotes autophagy occurrence and thus protects tumor cell survival under glucose deficiency. Clinical analysis indicates that both GFAT1 and TAB1 S438 phosphorylation levels correlate with the poor prognosis of lung adenocarcinoma patients. These findings altogether uncover an unidentified mechanism underlying p38 MAPK signaling regulation by metabolic enzyme upon nutrient stress and provide theoretical rationality of targeting GFAT1 for cancer treatment.

FGFR/RACK1 interacts with MDM2, promotes P53 degradation, and inhibits cell senescence in lung squamous cell carcinoma.

OBJECTIVE: FGFR is considered an important driver gene of lung squamous cell carcinoma (LSCC). Thus, identification of the biological events downstream of FGFR is important for the treatment of this malignancy. Our previous study has shown that the FGFR/RACK1 complex interacts with PKM2 and consequently promotes glycolysis in LSCC cells. However, the biological functions of the FGFR/RACK1 complex remain poorly understood. METHODS: Anchorage-independent assays and in vivo tumorigenesis assays were performed to evaluate cancer cell malignancy. Distant seeding assays were performed to evaluate cancer cell metastasis. ß-gal staining was used to examine cell senescence, and immunoprecipitation assays were performed to examine the interactions among FGFR, RACK1, and MDM2. RESULTS: FGFR/RACK1 was found to regulate the senescence of LSCC cells. Treatment with PD166866, an inhibitor of FGFR, or knockdown of RACK1 induced senescence in LSCC cells (P < 0.01). A molecular mechanistic study showed that FGFR/RACK1/MDM2 form a complex that promotes the degradation of p53 and thus inhibits cell senescence. PD166866 and RG7112, an MDM2/p53 inhibitor, cooperatively inhibited the colony formation and distal seeding of LSCC cells (P < 0.01), and upregulated the expression of p53 and p21. CONCLUSIONS: Together, our findings revealed the regulatory roles and mechanisms of FGFR/RACK1 in cell senescence. This understanding should be important in the treatment of LSCC.

Upregulated METTL3 in nasopharyngeal carcinoma enhances the motility of cancer cells.

The roles of RNA m6A modification in carcinogenesis have attracted much interest recently. However, the dysregulation of RNA m6A regulators (writers, readers, and erasers) in nasopharyngeal carcinoma (NPC) has never been reported. In this study, we showed that METTL3, one of the writers, was upregulated in NPC. Functional studies revealed that METTL3 promoted the migration and invasion of NPC cells. However, METTL3 knockdown reversed this effect and inhibited the migration, invasion and metastasis of NPC cells. METTL3 activated the luciferase activity of TOPflash (a reporter for beta-catenin/TCF signaling), and downregulation of METTL3 inhibited the expression of beta-catenin/TCF target genes vimentin and N-cadherin, which are two regulators of epithelial-mesenchymal transition. Moreover, dominant negative beta-catenin blocked the migration and invasion of NPC cells. Further mechanistic studies showed that METTL3 silencing decreased the m6A methylation and total mRNA levels of Tankyrase, a negative regulator of axin. Moreover, Tankyrase overexpression abrogated the repressive effects of METTL3 silencing on the migration of NPC cells. Collectively, our study demonstrates the oncogenic roles of METTL3 in NPC, and suggests that METTL3 might be a therapeutic target for NPC.

Artesunate inhibits the mevalonate pathway and promotes glioma cell senescence.

Glioma is a common brain malignancy for which new drug development is urgently needed because of radiotherapy and drug resistance. Recent studies have demonstrated that artemisinin (ARS) compounds can display antiglioma activity, but the mechanisms are poorly understood. Using cell lines and mouse models, we investigated the effects of the most soluble ARS analogue artesunate (ART) on glioma cell growth, migration, distant seeding and senescence and elucidated the underlying mechanisms. Artemisinin effectively inhibited glioma cell growth, migration and distant seeding. Further investigation of the mechanisms showed that ART can influence glioma cell metabolism by affecting the nuclear localization of SREBP2 (sterol regulatory element-binding protein 2) and the expression of its target gene HMGCR (3-hydroxy-3-methylglutaryl coenzyme A reductase), the rate-limiting enzyme of the mevalonate (MVA) pathway. Moreover, ART affected the interaction between SREBP2 and P53 and restored the expression of P21 in cells expressing wild-type P53, thus playing a key role in cell senescence induction. In conclusion, our study demonstrated the new therapeutic potential of ART in glioma cells and showed the novel anticancer mechanisms of ARS compounds of regulating MVA metabolism and cell senescence.

PAK4 Phosphorylates Fumarase and Blocks TGFß-Induced Cell Growth Arrest in Lung Cancer Cells.

The metabolic activity of fumarase (FH) participates in gene transcription linking to tumor cell growth. However, whether this effect is implicated in lung cancer remains unclear. Here, we show TGFß induces p38-mediated FH phosphorylation at Thr 90, which leads to a FH/CSL (also known as RBP-Jκ)/p53 complex formation and FH accumulation at p21 promoter under concomitant activation of Notch signaling; in turn, FH inhibits histone H3 Lys 36 demethylation and thereby promotes p21 transcription and cell growth arrest. In addition, FH is massively phosphorylated at the Ser 46 by PAK4 in non-small cell lung cancer (NSCLC) cells, and PAK4-phosphorylated FH binds to 14-3-3, resulting in cytosolic detention of FH and prohibition of FH/CSL/p53 complex formation. Physiologically, FH Ser 46 phosphorylation promotes tumorigenesis through its suppressive effect on FH Thr 90 phosphorylation-mediated cell growth arrest in NSCLC cells and correlates with poor prognosis in patients with lung cancer. Our findings uncover an uncharacterized mechanism underlying the local effect of FH on TGFß-induced gene transcription, on which the inhibitory effect from PAK4 promotes tumorigenesis in lung cancer. SIGNIFICANCE: Fumarase counteracts CSL via its metabolic activity to facilitate TGFß-induced cell growth arrest, an effect largely blocked by PAK4-mediated phosphorylation of fumarase.