The microRNA-182-PDK4 axis regulates lung tumorigenesis by modulating pyruvate dehydrogenase and lipogenesis

Inhibition of Pyruvate Dehydrogenase Kinase 4 Protects Cardiomyocytes from lipopolysaccharide-Induced Mitochondrial Damage by Reducing Lactate Accumulation

Mitochondrial dysfunction is considered one of the major pathogenic mechanisms of sepsis-induced cardiomyopathy (SIC). Pyruvate dehydrogenase kinase 4 (PDK4), a key regulator of mitochondrial metabolism, is essential for maintaining mitochondrial function. However, its specific role in SIC remains unclear. To investigate this, we established an in vitro model of septic cardiomyopathy using lipopolysaccharide (LPS)-induced H9C2 cardiomyocytes. Our study revealed a significant increase in PDK4 expression in LPS-treated H9C2 cardiomyocytes. Inhibiting PDK4 with dichloroacetic acid (DCA) improved cell survival, reduced intracellular lipid accumulation and calcium overload, and restored mitochondrial structure and respiratory capacity while decreasing lactate accumulation. Similarly, Oxamate, a lactate dehydrogenase inhibitor, exhibited similar effects to DCA in LPS-treated H9C2 cardiomyocytes. To further validate whether PDK4 causes cardiomyocyte and mitochondrial damage in SIC by promoting lactate production, we upregulated PDK4 expression using PDK4-overexpressing lentivirus in H9C2 cardiomyocytes. This resulted in elevated lactate levels, impaired mitochondrial structure, and reduced mitochondrial respiratory capacity. However, inhibiting lactate production reversed the mitochondrial dysfunction caused by PDK4 upregulation. In conclusion, our study highlights the pathogenic role of PDK4 in LPS-induced cardiomyocyte and mitochondrial damage by promoting lactate production. Therefore, targeting PDK4 and its downstream product lactate may serve as promising therapeutic approaches for treating SIC.

circFTO from M2 macrophage-derived small extracellular vesicles (sEV) enhances NSCLC malignancy by regulation miR-148a-3pPDK4 axis

BACKGROUND

Accumulation studies found that tumor-associated macrophages (TAMs) are a predominant cell in tumor microenvironment (TME), which function essentially during tumor progression. By releasing bioactive molecules, including circRNA, small extracellular vesicles (sEV) modulate immune cell functions in the TME, thereby affecting non-small cell lung cancer (NSCLC) progression. Nevertheless, biology functions and molecular mechanisms of M2 macrophage-derived sEV circRNAs in NSCLC are unclear.

METHODS

Cellular experiments were conducted to verify the M2 macrophage-derived sEV (M2-EV) roles in NSCLC. Differential circRNA expression in M0 and M2-EV was validated by RNA sequencing. circFTO expression in NSCLC patients and cells was investigated via real-time PCR and FISH. The biological mechanism of circFTO in NSCLC was validated by experiments. Our team isolated sEV from M2 macrophages (M2Ms) and found that M2-EV treatment promoted NSCLC CP, migration, and glycolysis.

RESULTS

High-throughput sequencing found that circFTO was highly enriched in M2-EV. FISH and RT-qPCR confirmed that circFTO expression incremented in NSCLC tissues and cell lines. Clinical studies confirmed that high circFTO expression correlated negatively with NSCLC patient survival. Luciferase reporter analysis confirmed that miR-148a-3p and PDK4 were downstream targets of circFTO. circFTO knockdown inhibited NSCLC cell growth and metastasis in in vivo experiments. Downregulating miR-148a-3p or overexpressing PDK4 restored the malignancy of NSCLC, including proliferation, migration, and aerobic glycolysis after circFTO silencing.

CONCLUSION

The study found that circFTO from M2-EV promoted NSCLC cell progression and glycolysis through miR-148a-3p/PDK4 axis. circFTO is a promising prognostic and diagnostic NSCLC biomarker and has the potential to be a candidate NSCLC therapy target.

The Implication of Growth Arrest-Specific 5 rs145204276 Polymorphism and Serum Expression of Sirtuin 1, Transforming Growth Factor-Beta, and microRNA-182 in Breast Cancer

Background

Breast cancer (BC) patients have a higher chance of survival if it is diagnosed at an early stage, which is essential for efficient treatment of the condition. The results of an elevated risk of cancer, including BC, previously associated with the ins/del polymorphism rs145204276 in the promoter region of growth arrest-specific 5 (GAS5) are still up for debate. Thus, this study aimed to appraise the frequency of the GAS5 rs145204276 variant with BC risk and demonstrate the potential impact of the sirtuin 1 (SIRT-1), transforming growth factor-beta (TGF-β), and microRNA-182 (miR-182) expression and their diagnostic value in BC.

Methods

Blood samples of 155 patients with BC and fibroadenoma and 80 healthy controls were analyzed for GAS5 rs145204276 single nucleotide polymorphism (SNP), SIRT-1, TGF-β, and miRNA-182 expression levels.

Results

Ins/ins genotype and ins allele frequencies for GAS5 rs145204276 were considerably higher in BC patients compared with controls. Patients with BC had significantly greater serum levels of TGF-β, miR-182, and SIRT-1 expression.

Conclusions

The SIRT-1, TGF-β, and miR-182 genes provide novel, noninvasive diagnostic biomarkers for BC.

PDK4-dependent hypercatabolism and lactate production of senescent cells promotes cancer malignancy

Senescent cells remain metabolically active, but their metabolic landscape and resulting implications remain underexplored. Here, we report upregulation of pyruvate dehydrogenase kinase 4 (PDK4) upon senescence, particularly in some stromal cell lines. Senescent cells display a PDK4-dependent increase in aerobic glycolysis and enhanced lactate production but maintain mitochondrial respiration and redox activity, thus adopting a special form of metabolic reprogramming. Medium from PDK4+ stromal cells promotes the malignancy of recipient cancer cells in vitro, whereas inhibition of PDK4 causes tumor regression in vivo. We find that lactate promotes reactive oxygen species production via NOX1 to drive the senescence-associated secretory phenotype, whereas PDK4 suppression reduces DNA damage severity and restrains the senescence-associated secretory phenotype. In preclinical trials, PDK4 inhibition alleviates physical dysfunction and prevents age-associated frailty. Together, our study confirms the hypercatabolic nature of senescent cells and reveals a metabolic link between cellular senescence, lactate production, and possibly, age-related pathologies, including but not limited to cancer.

High glucose promotes benign prostatic hyperplasia by downregulating PDK4 expression

As men age, a growing number develop benign prostatic hyperplasia (BPH). According to previous research, diabetes may be a risk factor. Pyruvate dehydrogenase kinase 4 (PDK4) is closely related to glucose metabolism and plays a role in the onset and progression of numerous illnesses. This study aimed to determine the direct effects of high glucose environment on prostate epithelial cells, in particular by altering PDK4 expression levels. In this investigation, normal prostatic epithelial cells (RWPE-1) and human benign prostatic hyperplasia epithelial cells (BPH-1) were treated with 50 mM glucose to show the alteration of high glucose in prostate cells. PDK4-target siRNA, PDK4-expression plasmid were used to investigate the effects of PDK4. Rosiglitazone (RG), a PPARγ agonist, with the potential to up-regulate PDK4 expression was also used for treating prostate cells. The expression of PDK4 in human prostate samples was also analyzed. The effects of high glucose therapy on BPH-1 and RWPE-1 cells were demonstrated to enhance proliferation, epithelial-mesenchymal transition (EMT), suppress apoptosis, and down-regulate PDK4 expression. Additionally, diabetes-related BPH patients had reduced PDK4 expression. Following the application of PDK4-target siRNA, a comparable outcome was seen. The PDK4-expression plasmid therapy, however, produced the opposite results. RG with the ability to elevate PDK4 expression might be used to treat BPH. Changes in the metabolism of lipids and glucose may be the cause of these consequences. These findings showed that high glucose treatment might facilitate BPH development, and may be related to the down-regulation of PDK4. PDK4 might be a potential therapeutic target of BPH.

Huangqi-Danshen decoction reshapes renal glucose metabolism profiles that delays chronic kidney disease progression

Huangqi-Danshen decoction (HDD), a Chinese herbal preparation, is effective in clinical treatment of chronic kidney disease (CKD). However, the underlying mechanism remains to be clarified. In this study, we aimed to investigate the role of HDD in the regulation of renal glucose metabolism in a CKD mouse model. The 0.2% adenine-induced CKD mouse model was administered HDD extract at a dose of 6.8 g/kg/day for 4 weeks. Detection of renal glucose metabolites was performed by ultra-performance liquid chromatography-tandem mass spectrometry. The expression of renal fibrosis and glucose metabolism-related proteins was tested by Western blotting, immunohistochemistry, and immunofluorescence. The results showed that HDD treatment could significantly reduce serum creatinine (0.36 ± 0.10 mg/dL vs. 0.51 ± 0.07 mg/dL, P < 0.05) and blood urea nitrogen (40.02 ± 3.73 mg/dL vs. 62.91 ± 10 mg/dL, P < 0.001) levels, and improve renal pathological injury and fibrosis. Aberrant glucose metabolism was found in the kidneys of CKD mice, manifested by enhanced glycolysis and pentose phosphate pathway, and tricarboxylic acid cycle inhibition, which could be partially restored by HDD treatment. Furthermore, HDD regulated the expression of hexokinase 2, phosphofructokinase, pyruvate kinase M2, pyruvate dehydrogenase E1, oxoglutarate dehydrogenase, and glucose-6-phosphate dehydrogenase in CKD mice. In conclusion, HDD protected against adenine-induced CKD, reshaped glucose metabolism profiles, and restored the expression of key enzymes of glucose metabolism in the kidneys of CKD mice. This study sheds light on targeting glucose metabolism for the treatment of CKD and screening small molecule compounds from herbal medicine to slow CKD progression.

Identification of Basement Membrane-Related Signatures in Gastric Cancer

BACKGROUND

The basement membrane (BM) serves as a major barrier to impede tumor cell invasion and extravasation during metastasis. However, the associations between BM-related genes and GC remain unclear.

METHODS

RNA expression data and corresponding clinical information of STAD samples were downloaded from the TCGA database. We identified BM-related subtypes and constructed a BM-related gene prognostic model using lasso-Cox regression analysis. We also investigated the single-cell properties of prognostic-related genes and the TME characteristic, TMB status, and chemotherapy response in high- and low-risk groups. Finally, we verified our results in the GEPIA database and human tissue specimens.

RESULTS

A six-gene lasso Cox regression model (APOD, CAPN6, GPC3, PDK4, SLC7A2, SVEP1) was developed. Activated CD4+ T cells and follicular T cells were shown to infiltrate more widely in the low-risk group. The low-risk group harbored significantly higher TMB and better prognosis, favoring immunotherapy.

CONCLUSIONS

We constructed a six-gene BM-related prognostic model for predicting GC prognosis, immune cell infiltration, TMB status, and chemotherapy response. This research provides new ideas for developing more effective individualized treatment of GC patients.

Pyruvate Dehydrogenase Kinase 4 Deficiency Increases Tumorigenesis in a Murine Model of Bladder Cancer

Pyruvate dehydrogenase kinase 4 (PDK4) is a mitochondrial isozyme in the PDK family (PDK1-4) partially responsible for phosphorylation of pyruvate dehydrogenase (PDH). Phosphorylation of PDH is thought to result in a pro-proliferative shift in metabolism that sustains growth of cancer cells. Previous data from our lab indicate the pan-PDK inhibitor dichloroacetate (DCA) or acute genetic knockdown of PDK4 blocks proliferation of bladder cancer (BCa) cells. The goal of this study was to determine the role of PDK4 in an in vivo BCa model, with the hypothesis that genetic depletion of PDK4 would impair formation of BCa. PDK4-/- or WT animals were exposed to N-Butyl-N-(4-hydroxybutyl) nitrosamine (BBN) for 16 weeks, and tumors were allowed to develop for up to 7 additional weeks. PDK4-/- mice had significantly larger tumors at later time points. When animals were treated with cisplatin, PDK4-/- animals still had larger tumors than WT mice. PDK4 expression was assessed in human tissue and in mice. WT mice lost expression of PDK4 as tumors became muscle-invasive. Similar results were observed in human samples, wherein tumors had less expression of PDK4 than benign tissue. In summary, PDK4 has a complex, multifunctional role in BCa and may represent an underrecognized tumor suppressor.

The pyruvate dehydrogenase complex: Life's essential, vulnerable and druggable energy homeostat

Found in all organisms, pyruvate dehydrogenase complexes (PDC) are the keystones of prokaryotic and eukaryotic energy metabolism. In eukaryotic organisms these multi-component megacomplexes provide a crucial mechanistic link between cytoplasmic glycolysis and the mitochondrial tricarboxylic acid (TCA) cycle. As a consequence, PDCs also influence the metabolism of branched chain amino acids, lipids and, ultimately, oxidative phosphorylation (OXPHOS). PDC activity is an essential determinant of the metabolic and bioenergetic flexibility of metazoan organisms in adapting to changes in development, nutrient availability and various stresses that challenge maintenance of homeostasis. This canonical role of the PDC has been extensively probed over the past decades by multidisciplinary investigations into its causal association with diverse physiological and pathological conditions, the latter making the PDC an increasingly viable therapeutic target. Here we review the biology of the remarkable PDC and its emerging importance in the pathobiology and treatment of diverse congenital and acquired disorders of metabolic integration.

PDK1- and PDK2-mediated metabolic reprogramming contributes to the TGFβ1-promoted stem-like properties in head and neck cancer

BACKGROUND

Resistance to chemotherapeutic drugs is a key factor for cancer recurrence and metastases in head and neck cancer (HNC). Cancer stem cells (CSCs) in tumors have self-renewal, differentiation, and higher drug resistance capabilities, resulting in a poor prognosis for patients. In glucose metabolism, pyruvate dehydrogenase kinase (PDK) inhibits pyruvate dehydrogenase and impedes pyruvate from being metabolized into acetyl-CoA and entering the tricarboxylic acid cycle to generate energy. Studies have reported that PDK1 and PDK2 inhibition suppresses the growth, motility, and drug resistance of cancer cells. Furthermore, while TGFβ1 levels are persistently elevated in HNC patients with poor prognosis, the role of PDK isoforms in the TGFβ1-promoted progression and stem-like properties of HNC is unclear.

METHODS

Levels of PDK1 and PDK2 were evaluated in HNC tissue microarrays by immunohistochemistry to explore potential clinical relevance. PDK1 and PDK2 were knocked down by the lentivirus shRNA system to investigate their role in TGFβ1-promoted tumor progression in vitro.

RESULTS

We found that PDK2 levels were increased in the later stage of HNC tissues compared to constant PDK1 expression. After PDK1 and PDK2 knockdown, we discovered increased ATP production and decreased lactate production in TGFβ1-treated and untreated HNC cells. However, only PDK2 silencing significantly inhibited the clonogenic ability of HNC cells. We subsequently found that TGFβ1-promoted migration and invasion capabilities were decreased in PDK1 and PDK2 knockdown cells. The tumor spheroid-forming capability, motility, CSC genes, and multidrug-resistant genes were downregulated in PDK1 and PDK2 silencing CSCs. PDK1 and PDK2 inhibition reversed cisplatin and gemcitabine resistance of CSCs, but not paclitaxel resistance.

CONCLUSION

The results demonstrated that the PDK1- and PDK2-mediated Warburg effect contributes to the TGFβ1-enhanced stemness properties of HNC. Therefore, PDK1 and PDK2 may serve as molecular targets for the combination therapy of HNC.

Elevated Level of Cerebrospinal Fluid Pyruvate Dehydrogenase Kinase 4 Is a Predictive Biomarker of Clinical Outcome after Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is a central nervous system disease with high mortality and morbidity. Some independent factors valuable for prognosis prediction in patients with SAH are still lacking. In our earlier study, we found that PDK4 exerts a protective effect after SAH, primarily by reducing oxidative stress and neuronal death via the ROS/ASK1/p38 signaling pathway. Therefore, we investigated the changes in the level of pyruvate dehydrogenase kinase 4 (PDK4) in patients after subarachnoid hemorrhage (SAH) and analyzed the value of the cerebrospinal fluid (CSF) PDK4 level in predicting the prognoses of patients with SAH after interventional embolization surgery. Some knee arthritis subjects who needed surgery were recruited as a control group. The results showed that PDK4 expression was elevated in the CSF of SAH patients compared with that of controls. PDK4 levels in CSF (OR = 4.525; 95% CI: 1.135-18.038; p = 0.032), time to surgery (OR = 0.795; 95% CI: 0.646-0.977; p = 0.029), and initial GCS scores (OR = 2.758; 95% CI: 0.177-43.106; p = 0.469) were independent prognostic risk factors for SAH patients after surgery. The receiver operating characteristic (ROC) curve showed PDK4 levels in CSF had a higher predictive value. Thus, PDK4 in CSF could be an independent prognostic risk factor for SAH patients after surgery. PDK4 has the potential to serve as a new therapeutic target and biomarker for use in the diagnosis of SAH severity and the prediction of recovery.

Anti-Metastatic Effect of Pyruvate Dehydrogenase Kinase 4 Inhibition in Bladder Cancer via the ERK, SRC, and JNK Pathways

Bladder cancer is a common global cancer with a high percentage of metastases and high mortality rate. Thus, it is necessary to identify new biomarkers that can be helpful in diagnosis. Pyruvate dehydrogenase kinase 4 (PDK4) belongs to the PDK family and plays an important role in glucose utilization in living organisms. In the present study, we evaluated the role of PDK4 in bladder cancer and its related protein changes. First, we observed elevated PDK4 expression in high-grade bladder cancers. To screen for changes in PDK4-related proteins in bladder cancer, we performed a comparative proteomic analysis using PDK4 knockdown cells. In bladder cancer cell lines, PDK4 silencing resulted in a lower rate of cell migration and invasion. In addition, a PDK4 knockdown xenograft model showed reduced bladder cancer growth in nude mice. Based on our results, PDK4 plays a critical role in the metastasis and growth of bladder cancer cells through changes in ERK, SRC, and JNK.

miR-182 targeting reprograms tumor-associated macrophages and limits breast cancer progression

The protumor roles of alternatively activated (M2) tumor-associated macrophages (TAMs) have been well established, and macrophage reprogramming is an important therapeutic goal. However, the mechanisms of TAM polarization remain incompletely understood, and effective strategies for macrophage targeting are lacking. Here, we show that miR-182 in macrophages mediates tumor-induced M2 polarization and can be targeted for therapeutic macrophage reprogramming. Constitutive miR-182 knockout in host mice and conditional knockout in macrophages impair M2-like TAMs and breast tumor development. Targeted depletion of macrophages in mice blocks the effect of miR-182 deficiency in tumor progression while reconstitution of miR-182-expressing macrophages promotes tumor growth. Mechanistically, cancer cells induce miR-182 expression in macrophages by TGFβ signaling, and miR-182 directly suppresses TLR4, leading to NFκb inactivation and M2 polarization of TAMs. Importantly, therapeutic delivery of antagomiR-182 with cationized mannan-modified extracellular vesicles effectively targets macrophages, leading to miR-182 inhibition, macrophage reprogramming, and tumor suppression in multiple breast cancer models of mice. Overall, our findings reveal a crucial TGFβ/miR-182/TLR4 axis for TAM polarization and provide rationale for RNA-based therapeutics of TAM targeting in cancer.

The Role of MiRNA in Cancer: Pathogenesis, Diagnosis, and Treatment

Cancer is also determined by the alterations of oncogenes and tumor suppressor genes. These gene expressions can be regulated by microRNAs (miRNA). At this point, researchers focus on addressing two main questions: "How are oncogenes and/or tumor suppressor genes regulated by miRNAs?" and "Which other mechanisms in cancer cells are regulated by miRNAs?" In this work we focus on gathering the publications answering these questions. The expression of miRNAs is affected by amplification, deletion or mutation. These processes are controlled by oncogenes and tumor suppressor genes, which regulate different mechanisms of cancer initiation and progression including cell proliferation, cell growth, apoptosis, DNA repair, invasion, angiogenesis, metastasis, drug resistance, metabolic regulation, and immune response regulation in cancer cells. In addition, profiling of miRNA is an important step in developing a new therapeutic approach for cancer.

Lipid metabolism in cancer progression and therapeutic strategies

Dysregulated lipid metabolism represents an important metabolic alteration in cancer. Fatty acids, cholesterol, and phospholipid are the three most prevalent lipids that act as energy producers, signaling molecules, and source material for the biogenesis of cell membranes. The enhanced synthesis, storage, and uptake of lipids contribute to cancer progression. The rewiring of lipid metabolism in cancer has been linked to the activation of oncogenic signaling pathways and cross talk with the tumor microenvironment. The resulting activity favors the survival and proliferation of tumor cells in the harsh conditions within the tumor. Lipid metabolism also plays a vital role in tumor immunogenicity via effects on the function of the noncancer cells within the tumor microenvironment, especially immune‐associated cells. Targeting altered lipid metabolism pathways has shown potential as a promising anticancer therapy. Here, we review recent evidence implicating the contribution of lipid metabolic reprogramming in cancer to cancer progression, and discuss the molecular mechanisms underlying lipid metabolism rewiring in cancer, and potential therapeutic strategies directed toward lipid metabolism in cancer. This review sheds new light to fully understanding of the role of lipid metabolic reprogramming in the context of cancer and provides valuable clues on therapeutic strategies targeting lipid metabolism in cancer.

Role of miR-182/PDCD4 axis in aggressive behavior of prostate cancer in the African Americans

Background

Prostate cancer is one of the most commonly diagnosed cancers among men. African Americans (AA) are at an increased risk of developing prostate cancer compared to European Americans (EA). miRNAs play a critical role in these tumors, leading to tumor progression. In this study, we investigated the role of miR-182 in racial disparity in prostate cancer.

Results

We found significantly increased levels of miR-182 in prostate cancer tissues compared to BPH. Also, miR-182 shows increased expression in AA prostate cancer cell line and tissue samples compared to EA. We performed biochemical recurrence (BCR) - free survival time in AA and EA patients and found that high miR-182 expression had significantly shorter BCR-free survival than patients with low miR-182 expression (P = 0.031). To elucidate the role of miR-182, we knocked down miR-182 in EA (DU-145 and LNCaP) and AA (MDA-PCa-2b) cell lines and found an increase in apoptosis, arrest of the cell cycle, and inhibition of colony formation in the AA cell line to a greater extent than EA cell lines.

Conclusions

Our results showed that PDCD4 is a direct miR-182 target and its inhibition is associated with aggressiveness and high Gleason grade in prostate cancer among AA. These findings show that miR-182 is highly expressed in AA patients and miR-182 may be a target for effective therapy in AA patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-08723-6.

Analysis of microRNA Expression in Liquid-Based Cytology Samples May Be Useful for Primary Lung Cancer Diagnosis

OBJECTIVES

Bronchoscopy is frequently performed for patients suspected of having lung cancer; however, we sometimes fail to make a definitive diagnosis, resulting in additional invasive testing. Many studies indicate that microRNAs (miRs) are abnormally expressed in cancers. We examined the diagnostic value of 4 miRs (miR-21, miR-31, miR-182, and miR-183) extracted from liquid-based cytology (LBC) samples and validated whether they were diagnostically useful.

METHODS

We collected 18 surgically resected tissue samples and 136 LBC specimens obtained during bronchoscopic examination at Hiroshima University Hospital. We extracted RNA from these samples and compared the expression of 4 miRs by reverse transcription-quantitative polymerase chain reaction.

RESULTS

We confirmed that expression of the 4 miRs was significantly higher in cancer tissues than in tumor-adjacent normal tissues. We examined the expression of these miRs in 125 (cancer cases, 83; noncancer cases, 42) of 136 cytologic samples. Expression of all 4 miRs was significantly higher in patients with lung cancer than in those without lung cancer. Among samples judged as benign or indeterminate, levels of these miRs were also significantly higher in patients with lung cancer than in those without lung cancer.

CONCLUSIONS

The analysis of miR expression in LBC samples might be helpful for primary lung cancer diagnosis.

Pyruvate dehydrogenase kinase 4-mediated metabolic reprogramming is involved in rituximab resistance in diffuse large B-cell lymphoma by affecting the expression of MS4A1/CD20

Diffuse large B cell lymphoma (DLBCL) heterogeneity promotes recurrence and anti‐CD20‐based therapeutic resistance. Previous studies have shown that downregulation of MS4A1/CD20 expression after chemoimmunotherapy with rituximab leads to rituximab resistance. However, the mechanisms of CD20 loss remain unknown. We identified that pyruvate dehydrogenase kinase 4 (PDK4) is markedly elevated in DLBCL cells derived from both patients and cell lines with R‐CHOP (rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone) resistance. We found that overexpression of PDK4 in DLBCL cells resulted in cell proliferation and resistance to rituximab in vitro and in vivo. Furthermore, loss of PDK4 expression or treatment with the PDK4 inhibitor dichloroacetate was able to significantly increase rituximab‐induced cell apoptosis in DLBCL cells. Further studies suggested PDK4 mediates a metabolic shift, in that the main energy source was changed from oxidative phosphorylation to glycolysis, and the metabolic changes could play an important role in rituximab resistance. Importantly, by knocking down or overexpressing PDK4 in DLBCL cells, we showed that PDK4 has a negative regulation effect on MS4A1/CD20 expression. Collectively, this is the first study showing that targeting PDK4 has the potential to overcome rituximab resistance in DLBCL.

Increased Expression of PDK4 Was Displayed in Gastric Cancer and Exhibited an Association With Glucose Metabolism

Previous studies reported that pyruvate dehydrogenase kinase 4 (PDK4) is closely related to diabetes, heart disease, and carcinomas. Nevertheless, the role of PDK4 in gastric cancer (GC) occurrence and development is yet poorly understood. Our experiments were taken to evaluate PDK4's function in GC. The Cancer Genome Atlas tumor genome map database was employed to validate the levels of PDK family in different grades and stages of GC. The survival ratio of PDK families in GC was detected by the Kaplan-Meier plotter database. The links existing in the expression of PDK family and the level of tumor-infiltrating immune cells were investigated by tumor immunity assessment resource (TIMER). PDK4-associated signal pathways in GC were analyzed by the Kyoto Encyclopedia of Genes and Genomes pathway analysis. PDK4 mRNA level in the GC cells was measured by qRT-PCR. Cell counting kit-8 and Transwell assays were separately carried out to evaluate PDK4-induced influence on GC cell proliferation, migration, and invasion. Our data suggested that GC cells highly expressed PDK4, and PDK4 expression presented a significant relation with the staging, grade, and survival rate of GC. PDK4 expression presented a positive correlation with the types of different infiltrating immune cells, comprising B cells, CD4+ T cells, and dendritic cells. Meanwhile, PDK4 expression exhibited a strong association with macrophages. Survival analysis revealed that the expression of PDK4 displayed a relationship with the prognosis of patients. Therefore, PDK4 was liable to be a biomarker for prognosis. Our results further displayed that PDK4 might modulate the glycolysis level in GC cells, and its expression was associated with GC cell proliferation, migration, and invasion. These data may provide insights into designing a new treatment strategy for GC.

Targeting pyruvate dehydrogenase kinase signaling in the development of effective cancer therapy

Pyruvate is irreversibly decarboxylated to acetyl coenzyme A by mitochondrial pyruvate dehydrogenase complex (PDC). Decarboxylation of pyruvate is considered a crucial step in cell metabolism and energetics. The cancer cells prefer aerobic glycolysis rather than mitochondrial oxidation of pyruvate. This attribute of cancer cells allows them to sustain under indefinite proliferation and growth. Pyruvate dehydrogenase kinases (PDKs) play critical roles in many diseases because they regulate PDC activity. Recent findings suggest an altered metabolism of cancer cells is associated with impaired mitochondrial function due to PDC inhibition. PDKs inhibit the PDC activity via phosphorylation of the E1a subunit and subsequently cause a glycolytic shift. Thus, inhibition of PDK is an attractive strategy in anticancer therapy. This review highlights that PDC/PDK axis could be implicated in cancer's therapeutic management by developing potential small-molecule PDK inhibitors. In recent years, a dramatic increase in the targeting of the PDC/PDK axis for cancer treatment gained an attention from the scientific community. We further discuss breakthrough findings in the PDC-PDK axis. In addition, structural features, functional significance, mechanism of activation, involvement in various human pathologies, and expression of different forms of PDKs (PDK1-4) in different types of cancers are discussed in detail. We further emphasized the gene expression profiling of PDKs in cancer patients to prognosis and therapeutic manifestations. Additionally, inhibition of the PDK/PDC axis by small molecule inhibitors and natural compounds at different clinical evaluation stages has also been discussed comprehensively.

Glioma glycolipid metabolism: MSI2-SNORD12B-FIP1L1-ZBTB4 feedback loop as a potential treatment target

Abnormal energy metabolism, including enhanced aerobic glycolysis and lipid synthesis, is a well-established feature of glioblastoma (GBM) cells. Thus, targeting the cellular glycolipid metabolism can be a feasible therapeutic strategy for GBM. This study aimed to evaluate the roles of MSI2, SNORD12B, and ZBTB4 in regulating the glycolipid metabolism and proliferation of GBM cells. MSI2 and SNORD12B expression was significantly upregulated and ZBTB4 expression was significantly low in GBM tissues and cells. Knockdown of MSI2 or SNORD12B or overexpression of ZBTB4 inhibited GBM cell glycolipid metabolism and proliferation. MSI2 may improve SNORD12B expression by increasing its stability. Importantly, SNORD12B increased utilization of the ZBTB4 mRNA transcript distal polyadenylation signal in alternative polyadenylation processing by competitively combining with FIP1L1, which decreased ZBTB4 expression because of the increased proportion of the 3' untranslated region long transcript. ZBTB4 transcriptionally suppressed the expression of HK2 and ACLY by binding directly to the promoter regions. Additionally, ZBTB4 bound the MSI promoter region to transcriptionally suppress MSI2 expression, thereby forming an MSI2/SNORD12B/FIP1L1/ZBTB4 feedback loop to regulate the glycolipid metabolism and proliferation of GBM cells. In conclusion, MSI2 increased the stability of SNORD12B, which regulated ZBTB4 alternative polyadenylation processing by competitively binding to FIP1L1. Thus, the MSI2/SNORD12B/FIP1L1/ZBTB4 positive feedback loop plays a crucial role in regulating the glycolipid metabolism of GBM cells and provides a potential drug target for glioma treatment.

The Role of MicroRNAs in Lung Cancer Metabolism

MicroRNAs (miRNAs) are short-strand non-coding RNAs that are responsible for post-transcriptional regulation of many biological processes. Their differential expression is important in supporting tumorigenesis by causing dysregulation in normal biological functions including cell proliferation, apoptosis, metastasis and invasion and cellular metabolism. Cellular metabolic processes are a tightly regulated mechanism. However, cancer cells have adapted features to circumvent these regulations, recognizing metabolic reprogramming as an important hallmark of cancer. The miRNA expression profile may differ between localized lung cancers, advanced lung cancers and solid tumors, which lead to a varying extent of metabolic deregulation. Emerging evidence has shown the relationship between the differential expression of miRNAs with lung cancer metabolic reprogramming in perpetuating tumorigenesis. This review provides an insight into the role of different miRNAs in lung cancer metabolic reprogramming by targeting key enzymes, transporter proteins or regulatory components alongside metabolic signaling pathways. These discussions would allow a deeper understanding of the importance of miRNAs in tumor progression therefore providing new avenues for diagnostic, therapeutic and disease management applications.

MiR-122-5p suppresses neuropathic pain development by targeting PDK4

The complex pathogenesis and limited efficacy of available treatment make neuropathic pain difficult for long periods of time. Several findings suggested the regulatory role of microRNA in the development of neuropathic pain. This study aims to investigate the functional role of miR-122-5p in the development of neuropathic pain. Down-regulation of miR-122-5p was observed in spinal cords of rats with neuropathic pain. We also found that overexpressing miR-122-5p by intrathecal injection of miR-122-5p lentivirus in a mouse model of chronic sciatic nerve injury (CCI) prevented neuropathic pain behavior. In HEK-293 T cells, luciferase activity was significantly decreased in the transfection group with mimic-miR-122-5p in wild-type PDK4 reporter, compared with mutant PDK4 reporter. Increased PDK4 expression was also observed during the progression of neuropathic pain. Intrathecal injection of both mimic-miR-122-5p and shPDK4 in CCI mice downregulated PDK4 expression to a lower level when compared with injected with shPDK4. In CCI mice, transfection of shPDK4 suppressed mechanical allodynia and thermal hyperalgesia, while co-transfection of shPDK4 and LV-miR-122-5p resulted in stronger levels of mechanical allodynia and thermal hyperalgesia inhibition. Taken together, the data suggest that miR-122-5p inhibits PDK4 expression, attenuating neuropathic pain. This result suggests the potential role of miR-122-5p acting as a target for the treatment of neuropathic pain.

Role of Aberrant Lipid Metabolism of Cancer Stem Cells in Cancer Progression

Cancer stem cells (CSCs) represent a small population of cancer cells that are able to self-renew and initiate tumors, which undergo epigenetic, epithelial-mesenchymal, immunological, and metabolic reprogramming to adapt to the tumor microenvironment as well as survive host defense or therapeutic insults. The metabolic reprogramming that accompanies cancer onset is known to be critical for the disease pathogenesis. A coordinated dysregulation of lipid metabolism is observed in nearly all cancer types. In addition to fulfilling basic requirements of structural lipids for membrane synthesis, lipids function importantly as signaling molecules and contribute to energy homeostasis. In this review, we summarize the current progress in the attractive research field of aberrant lipid metabolism regarding CSCs in cancer progression, which provides insights into therapeutic agents targeting CSCs based upon their modulation of lipid metabolism.

Inhibition of lipogenesis and induction of apoptosis by valproic acid in prostate cancer cells via the C/EBPα/SREBP-1 pathway

Lipid metabolism reprogramming is now accepted as a new hallmark of cancer. Hence, targeting the lipogenesis pathway may be a potential avenue for cancer treatment. Valproic acid (VPA) emerges as a promising drug for cancer therapy; however, the underlying mechanisms are not yet fully understood. In this study, we aimed to investigate the effects and mechanisms of VPA on cell viability, lipogenesis, and apoptosis in human prostate cancer PC-3 and LNCaP cells. The results showed that VPA significantly reduced lipid accumulation and induced apoptosis of PC-3 and LNCaP cells. Moreover, the expression of CCAAT/enhancer-binding protein α (C/EBPα), as well as sterol regulatory element-binding protein 1 (SREBP-1) and its downstream effectors, including fatty acid synthase (FASN), acetyl CoA carboxylase 1 (ACC1), and anti-apoptotic B-cell lymphoma 2 (Bcl-2), was markedly decreased in PC-3 and LNCaP cells after VPA administration. Mechanistically, the overexpression of C/EBPα rescued the levels of SREBP-1, FASN, ACC1, and Bcl-2, enhanced lipid accumulation, and attenuated apoptosis of VPA-treated PC-3 cells. Conversely, knockdown of C/EBPα by siRNA further decreased lipid accumulation, enhanced apoptosis, and reduced the levels of SREBP-1, FASN, ACC1, and Bcl-2. In addition, SREBP-1a and 1c enhanced the expressions of FASN and ACC1, but only SREBP-1a had a significant effect on Bcl-2 expression in VPA-treated PC-3 cells. Based on the results, we concluded that VPA significantly inhibits cell viability via decreasing lipogenesis and inducing apoptosis via the C/EBPα/SREBP-1 pathway in prostate cancer cells. Therefore, VPA that targets lipid metabolism and apoptosis is a promising candidate for PCa chemotherapy.

Circ_0091579 enhances the malignancy of hepatocellular carcinoma via miR-1287/PDK2 axis

Several articles have indicated that circular RNAs are involved in pathogenesis of human cancers. Nevertheless, the role of circ_0091579 in hepatocellular carcinoma (HCC) progression remains to be revealed. Quantitative reverse transcriptase polymerase chain reaction was carried out to examine the expression of circ_0091579 and miR-1287. The proliferation of HCC cells was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Flow cytometry was performed to analyze cell cycle progression and apoptosis. Western blot assay was conducted to detect the protein expression of CyclinD1, Cleaved caspase3, and pyruvate dehydrogenase kinase 2 (PDK2). Cell glycolysis was evaluated by measuring the uptake of glucose, the production of lactate, and extracellular acidification rate. The target relationship between miR-1287 and circ_0091579 or PDK2 was verified by dual-luciferase reporter assay, RNA immunoprecipitation assay, and RNA-pull down assay. The enrichment of circ_0091579 was enhanced in HCC tissues (n = 77) and four HCC cell lines (HB611, Huh-7, MHCC97, and SNU423) compared with adjacent non-tumor tissues (n = 77) and normal human liver cell line THLE-2. Circ_0091579 mediated the promotion of proliferation and glycolysis and the suppression of apoptosis of HCC cells. MiR-1287 was a direct target of circ_0091579 in HCC cells. MiR-1287 knockdown reversed the effects caused by circ_0091579 interference on the functions of HCC cells. PDK2 could bind to miR-1287 in HCC cells. Circ_0091579 upregulated the enrichment of PDK2 by acting as a sponge of miR-1287 in HCC cells. The influence caused by circ_0091579 intervention on HCC cells was attenuated by overexpression of PDK2. Circ_0091579 interference impeded the progression of HCC in vivo. Circ_0091579 deteriorated HCC by promoting the proliferation and glycolytic metabolism and suppressing the apoptosis of HCC cells via miR-1287/PDK2 axis.

The pivotal role of MicroRNAs in glucose metabolism in cancer

Cancer cells are able to undergo aerobic glycolysis and metabolize glucose to lactate instead of oxidative phosphorylation, which is known as Warburg effect. Accumulating evidence has revealed that microRNAs regulate cancer cell metabolism, which manifest a higher rate of glucose metabolism. Various signaling pathways along with glycolytic enzymes are responsible for the emergence of glycolytic dependence. MicroRNAs are a class of non-coding RNAs that are not translated into proteins but regulate target gene expression or in other words function pre-translationally and post-transcriptionally. MicroRNAs have been shown to be involved in various biological processes, including glucose metabolism via targeting major transcription factors, enzymes, oncogenes or tumor suppressors alongside the oncogenic signaling pathways. In this review, we describe the regulatory role of microRNAs of cancer cell glucose metabolism, including in the glucose uptake, glycolysis, tricarboxylic acid cycle and several signaling pathways and further suggest that microRNA-based therapeutics can be used to inhibit the process of glucose metabolism reprogramming in cancer cells and thus suppressing cancer progression.

The Implications of PDK1-4 on Tumor Energy Metabolism, Aggressiveness and Therapy Resistance

A metabolic shift from oxidative phosphorylation (OXPHOS) to glycolysis-known as the Warburg effect-is characteristic for many cancers. It gives the cancer cells a survival advantage in the hypoxic tumor microenvironment and protects them from cytotoxic effects of oxidative damage and apoptosis. The main regulators of this metabolic shift are the pyruvate dehydrogenase complex and pyruvate dehydrogenase kinase (PDK) isoforms 1-4. PDK is known to be overexpressed in several cancers and is associated with bad prognosis and therapy resistance. Whereas the expression of PDK1-3 is tissue specific, PDK4 expression is dependent on the energetic state of the whole organism. In contrast to other PDK isoforms, not only oncogenic, but also tumor suppressive functions of PDK4 have been reported. In tumors that profit from high OXPHOS and high de novo fatty acid synthesis, PDK4 can have a protective effect. This is the case for prostate cancer, the most common cancer in men, and makes PDK4 an interesting therapeutic target. While most work is focused on PDK in tumors characterized by high glycolytic activity, little research is devoted to those cases where PDK4 acts protective and is therefore highly needed.

Oxidative Stress and Cancer Development: Are Noncoding RNAs the Missing Links?

Significance: It is now clear that genetic changes underlie the basis of cancer, and alterations in functions of multiple genes are responsible for the process of tumorigenesis. Besides the classical genes that are usually implicated in cancer, the role of noncoding RNAs (ncRNAs) and reactive oxygen species (ROS) as independent entitites has also been investigated. Recent Advances: The microRNAs and long noncoding RNAs (lncRNAs), two main classes of ncRNAs, are known to regulate many aspects of tumor development. ROS, generated during oxidative stress and pathological conditions, are known to regulate every step of tumor development. Conversely, oxidative stress and ROS producing agents can suppress tumor development. The malignant cells normally produce high levels of ROS compared with normal cells. The interaction between ROS and ncRNAs regulates the expression of multiple genes and pathways implicated in cancer, suggesting a unique mechanistic relationship among ncRNA-ROS-cancer. The mechanistic relationship has been reported in hepatocellular carcinoma, glioma, and malignancies of blood, breast, colorectum, esophagus, kidney, lung, mouth, ovary, pancreas, prostate, and stomach. The ncRNA-ROS regulate several cancer-related cell signaling pathways, namely, protein kinase B (AKT), epidermal growth factor receptor (EGFR), forkhead box O3 (FOXO3), kelch-like ECH-associated protein 1 (Keap1), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), nuclear factor erythroid 2-related factor 2 (Nrf2), p53, phosphatase and tensin homologue (PTEN), and wingless-related integration site (Wnt)/glycogen synthase kinase-3 beta (GSK3β). Critical Issues: To date, most of the reports about ncRNA-oxidative stress-carcinogenesis relationships are based on cell lines. The mechanistic basis for this relationship has not been completely elucidated. Future Directions: Attempts should be made to explore the association of lncRNAs with ROS. The significance of the ncRNA-oxidative stress-carcinogenesis interplay should also be explored through studies in animal models.

microRNA-9-5p regulates the mitochondrial function of hepatocellular carcinoma cells through suppressing PDK4

Due to the lack of early diagnostic and effective treatment modalities, hepatocellular carcinoma (HCC) is still the most lethal cancer with a high mortality on a global scale. Recent studies have highlighted the key roles of microRNAs (miRs) in HCC development. In the study, we attempted to investigate the potential role of miR-9-5p in the progression of HCC. Expression of pyruvate dehydrogenase kinase 4 (PDK4) and miR-9-5p was examined in HCC tissues collected from HCC patients and cell lines. The proliferation, migration, invasion, and apoptosis of HCC cells, and levels of oxygen consumption rate, extracellular acidification rate and reactive oxygen species (ROS) as well as the tumorigenicity of transfected cells in vivo were measured after gain- and loss-of-function experiments in HCC cells. It was revealed that miR-9-5p was upregulated, while PDK4 was poorly expressed in HCC tissues and cells, associating with a poor prognosis of HCC patients. miR-9-5p directly targeted PDK4 and could downregulate its expression, thus leading to promoted cell proliferation, invasion and migration, enhanced mitochondrial activity and energy metabolism, and suppressed apoptosis in HCC cells, along with increased tumorigenicity in mouse xenograft models. Altogether, miR-9-5p facilitated mitochondrial energy metabolism of HCC cells by downregulating PDK4, promoting the development of HCC. miR-9-5p and PDK4 may serve as potential therapeutic targets for preventing recurrence and metastasis of HCC.

Non-Coding and Regulatory RNAs as Epigenetic Remodelers of Fatty Acid Homeostasis in Cancer

Cancer cells commonly display metabolic fluctuations. Together with the Warburg effect and the increased glutaminolysis, alterations in lipid metabolism homeostasis have been recognized as a hallmark of cancer. Highly proliferative cancer cells upregulate de novo synthesis of fatty acids (FAs) which are required to support tumor progression by exerting multiple roles including structural cell membrane composition, regulators of the intracellular redox homeostasis, ATP synthesis, intracellular cell signaling molecules, and extracellular mediators of the tumor microenvironment. Epigenetic modifications have been shown to play a crucial role in human development, but also in the initiation and progression of complex diseases. The study of epigenetic processes could help to design new integral strategies for the prevention and treatment of metabolic disorders including cancer. Herein, we first describe the main altered intracellular fatty acid processes to support cancer initiation and progression. Next, we focus on the most important regulatory and non-coding RNAs (small noncoding RNA-sncRNAs-long non-coding RNAs-lncRNAs-and other regulatory RNAs) which may target the altered fatty acids pathway in cancer.

Immune Checkpoint Blockade Improves Chemotherapy in the PyMT Mammary Carcinoma Mouse Model

Despite the success of immune checkpoint blockade in cancer, the number of patients that benefit from this revolutionary treatment option remains low. Therefore, efforts are being undertaken to sensitize tumors for immune checkpoint blockade, which includes combining immune checkpoint blocking agents such as anti-PD-1 antibodies with standard of care treatments. Here we report that a combination of chemotherapy (doxorubicin) and immune checkpoint blockade (anti-PD-1 antibodies) induces superior tumor control compared to chemotherapy and immune checkpoint blockade alone in the murine autochthonous polyoma middle T oncogene-driven (PyMT) mammary tumor model. Using whole transcriptome analysis, we identified a set of genes that were upregulated specifically upon chemoimmunotherapy. This gene signature and, more specifically, a condensed four-gene signature predicted favorable survival of human mammary carcinoma patients in the METABRIC cohort. Moreover, PyMT tumors treated with chemoimmunotherapy contained higher levels of cytotoxic lymphocytes, particularly natural killer cells (NK cells). Gene set enrichment analysis and bead-based ELISA measurements revealed increased IL-27 production and signaling in PyMT tumors upon chemoimmunotherapy. Moreover, IL-27 signaling improved NK cell cytotoxicity against PyMT cells in vitro. Taken together, our data support recent clinical observations indicating a benefit of chemoimmunotherapy compared to monotherapy in breast cancer and suggest potential underlying mechanisms.

Revisiting cancer hallmarks: insights from the interplay between oxidative stress and non-coding RNAs

Cancer is one of the most common disease worldwide, with complex changes and certain traits which have been described as “The Hallmarks of Cancer.” Despite increasing studies on in-depth investigation of these hallmarks, the molecular mechanisms associated with tumorigenesis have still not yet been fully defined. Recently, accumulating evidence supports the observation that microRNAs and long noncoding RNAs (lncRNAs), two main classes of noncoding RNAs (ncRNAs), regulate most cancer hallmarks through their binding with DNA, RNA or proteins, or encoding small peptides. Reactive oxygen species (ROS), the byproducts generated during metabolic processes, are known to regulate every step of tumorigenesis by acting as second messengers in cancer cells. The disturbance in ROS homeostasis leads to a specific pathological state termed “oxidative stress”, which plays essential roles in regulation of cancer progression. In addition, the interplay between oxidative stress and ncRNAs is found to regulate the expression of multiple genes and the activation of several signaling pathways involved in cancer hallmarks, revealing a potential mechanistic relationship involving ncRNAs, oxidative stress and cancer. In this review, we provide evidence that shows the essential role of ncRNAs and the interplay between oxidative stress and ncRNAs in regulating cancer hallmarks, which may expand our understanding of ncRNAs in the cancer development from the new perspective.

MicroRNA and ROS Crosstalk in Cardiac and Pulmonary Diseases

Reactive oxygen species (ROS) affect many cellular functions and the proper redox balance between ROS and antioxidants contributes substantially to the physiological welfare of the cell. During pathological conditions, an altered redox equilibrium leads to increased production of ROS that in turn may cause oxidative damage. MicroRNAs (miRNAs) regulate gene expression at the post-transcriptional level contributing to all major cellular processes, including oxidative stress and cell death. Several miRNAs are expressed in response to ROS to mediate oxidative stress. Conversely, oxidative stress may lead to the upregulation of miRNAs that control mechanisms to buffer the damage induced by ROS. This review focuses on the complex crosstalk between miRNAs and ROS in diseases of the cardiac (i.e., cardiac hypertrophy, heart failure, myocardial infarction, ischemia/reperfusion injury, diabetic cardiomyopathy) and pulmonary (i.e., idiopathic pulmonary fibrosis, acute lung injury/acute respiratory distress syndrome, asthma, chronic obstructive pulmonary disease, lung cancer) compartments. Of note, miR-34a, miR-144, miR-421, miR-129, miR-181c, miR-16, miR-31, miR-155, miR-21, and miR-1/206 were found to play a role during oxidative stress in both heart and lung pathologies. This review comprehensively summarizes current knowledge in the field.

miR-16-5p/PDK4-Mediated Metabolic Reprogramming Is Involved in Chemoresistance of Cervical Cancer

Cervical cancer is one of the most prevalent malignancies in women worldwide. Therefore, investigation about molecular pathogenesis and related therapy targets of cervical cancer is an emergency. The molecular mechanisms responsible for the chemoresistance of cervical cancer were investigated by the use of doxorubicin (Dox)-resistant HeLa/Dox and SiHa/Dox cells. Our data showed that chemoresistant cells exhibited significantly higher glucose consumption, lactate production rate, and ATP levels than that of their parental cells. Among metabolic and glycolytic related genes, the expression of PDK4 was upregulated in Dox-resistant cells. Knockdown of PDK4 can decrease glucose consumption, lactate production rate, and ATP levels and further sensitize resistant cervical cancer cells to Dox treatment. By screening microRNAs (miRNAs), which can regulate expression of PDK4, we found that miR-16-5p was downregulated in chemoresistant cells. Overexpression of miR-16-5p can decrease the expression of PDK4 and sensitize the resistant cells to Dox treatment. Xenograft models confirmed that knockdown of PDK4 can increase chemotherapy efficiency for in vivo tumor growth. Collectively, our data suggested that miR-16-5p/PDK4-mediated metabolic reprogramming is involved in chemoresistance of cervical cancer.

Loss of PDK4 expression promotes proliferation, tumorigenicity, motility and invasion of hepatocellular carcinoma cells

Although the roles and underlying mechanisms of other PDK family members (i.e., PDK1, PDK2 and PDK3) in tumor progression have been extensively investigated and are well understood, the functions and underlying molecular mechanisms of pyruvate dehydrogenase kinase 4 (PDK4) in the tumorigenesis and progression of various cancers [including hepatocellular carcinoma (HCC)] remain largely unknown. In this study, we examined the expression profile of PDK4 in HCC clinical tissue specimens and the roles of PDK4 in the proliferation, tumorigenicity, motility and invasion of HCC cells. The immunohistochemistry (IHC) and quantitative real-time PCR (qRT-PCR) results revealed that PDK4 was significantly downregulated in the cohort of HCC clinical specimens. Additionally, PDK4 protein was found in both the nucleus and cytoplasm of HCC cells based on an immunofluorescence (ICC) assay, and PDK4 protein was also found in the nucleus and cytoplasm of cancer cells contained in HCC clinical specimens based on IHC. The CCK-8 assay and cell colony formation assay demonstrated that stable depletion of endogenous PDK4 by lentivirus-mediated RNA interference (RNAi) markedly promoted the proliferation of HCC cell lines (i.e., BEL-7402 and BEL-7404 cells) in vitro, while PDK4 silencing significantly enhanced the tumorigenic ability of BEL-7404 cells in vivo. In addition to enhance proliferation and tumorigenesis induced by PDK4 silencing, additional studies demonstrated that knockdown of PDK4 led to increase migration and invasion of BEL-7402 and BEL-7404 cells in vitro. Taken together, these findings suggest that the loss of PDK4 expression contributes to HCC malignant progression.

Non-Coding RNAs in Lung Tumor Initiation and Progression

Lung cancer is one of the deadliest forms of cancer affecting society today. Non-coding RNAs, such as microRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs), through the transcriptional, post-transcriptional, and epigenetic changes they impose, have been found to be dysregulated to affect lung cancer tumorigenesis and metastasis. This review will briefly summarize hallmarks involved in lung cancer initiation and progression. For initiation, these hallmarks include tumor initiating cells, immortalization, activation of oncogenes and inactivation of tumor suppressors. Hallmarks involved in lung cancer progression include metastasis and drug tolerance and resistance. The targeting of these hallmarks with non-coding RNAs can affect vital metabolic and cell signaling pathways, which as a result can potentially have a role in cancerous and pathological processes. By further understanding non-coding RNAs, researchers can work towards diagnoses and treatments to improve early detection and clinical response.

Subpopulation targeting of pyruvate dehydrogenase and GLUT1 decouples metabolic heterogeneity during collective cancer cell invasion

Phenotypic heterogeneity exists within collectively invading packs of tumor cells, suggesting that cellular subtypes cooperate to drive invasion and metastasis. Here, we take a chemical biology approach to probe cell:cell cooperation within the collective invasion pack. These data reveal metabolic heterogeneity within invasive chains, in which leader cells preferentially utilize mitochondrial respiration and trailing follower cells rely on elevated glucose uptake. We define a pyruvate dehydrogenase (PDH) dependency in leader cells that can be therapeutically exploited with the mitochondria-targeting compound alexidine dihydrochloride. In contrast, follower cells highly express glucose transporter 1 (GLUT1), which sustains an elevated level of glucose uptake required to maintain proliferation. Co-targeting of both leader and follower cells with PDH and GLUT1 inhibitors, respectively, inhibits cell growth and collective invasion. Taken together, our work reveals metabolic heterogeneity within the lung cancer collective invasion pack and provides rationale for co-targeting PDH and GLUT1 to inhibit collective invasion.

The presence of phenotypic heterogeneity in collectively invading cells suggests cooperation amongst distinct subtypes of cells to promote invasion and metastasis. Here, the authors use chemical biology tools and report metabolic heterogeneity within the lung cancer collective invasion pack.

The Implications of PDK1-4 on Tumor Energy Metabolism, Aggressiveness and Therapy Resistance

A metabolic shift from oxidative phosphorylation (OXPHOS) to glycolysis-known as the Warburg effect-is characteristic for many cancers. It gives the cancer cells a survival advantage in the hypoxic tumor microenvironment and protects them from cytotoxic effects of oxidative damage and apoptosis. The main regulators of this metabolic shift are the pyruvate dehydrogenase complex and pyruvate dehydrogenase kinase (PDK) isoforms 1-4. PDK is known to be overexpressed in several cancers and is associated with bad prognosis and therapy resistance. Whereas the expression of PDK1-3 is tissue specific, PDK4 expression is dependent on the energetic state of the whole organism. In contrast to other PDK isoforms, not only oncogenic, but also tumor suppressive functions of PDK4 have been reported. In tumors that profit from high OXPHOS and high de novo fatty acid synthesis, PDK4 can have a protective effect. This is the case for prostate cancer, the most common cancer in men, and makes PDK4 an interesting therapeutic target. While most work is focused on PDK in tumors characterized by high glycolytic activity, little research is devoted to those cases where PDK4 acts protective and is therefore highly needed.

MicroRNA-214 suppresses cell proliferation and migration and cell metabolism by targeting PDK2 and PHF6 in hepatocellular carcinoma

MiR-214 has been reported to act as a tumor suppressor or oncogene involved in various malignancies. However, the biological functions and molecular mechanisms of miR-214 in hepatocellular carcinoma (HCC) still remain unclear. Previous studies suggest that pyruvate dehydrogenase kinase 2 (PDK2) and plant homeodomain finger protein 6 (PHF6) may be involved in some tumor cell proliferation and migration. Therefore, we studied the relationship between PDK2/PHF6 and miR-214. The expression of miR-214, PDK2, and PHF6 was determined by quantitative real-time polymerase chain reaction in HCC tissues and cell lines. The Luciferase reporter assay was used to confirm the interaction between miR-214 and PDK2/PHF6. Cell proliferation, apoptosis, and migration were evaluated by cell counting kit-8 assay, flow cytometry, and transwell assay, respectively. The expressions levels of α-smooth muscle actin (α-SMA) and E-cadherin were detected via immunofluorescence assay. Here, we found that the expression of miR-214 decreased in HCC and was negatively correlated with PDK2 and PHF6. Moreover, PDK2 and PHF6 were the direct targets of miR-214 in HCC cells. Functional analysis showed that knockdown of PDK2 or PHF6 as well as miR-214 overexpression significantly suppressed cell proliferation and migration in HCC cells. Furthermore, we found that the suppression of cell proliferation and migration through PDK2 or PHF6 knockdown could be partially reversed by miR-214 down-regulation. Moreover, we demonstrated a decrease of mesenchymal cell marker α-SMA and increase of the epithelial marker E-cadherin after miR-214 overexpression, PDK2 knockdown or PHF6 knockdown, respectively, which also suggested that cell proliferation and migration were suppressed. Additionally, lactate and pyruvic acid production experiments confirmed miR-214 could suppress the HCC cell lactate and pyruvic acid levels by down-regulating PDK2/PHF6. In conclusion, MiR-214 may act as a tumor suppressor gene, presenting its suppressive role in cell proliferation and migration of HCC cells by targeting PDK2 and PHF6, and might provide a potential therapy target for patients with HCC.

The vital role of ATP citrate lyase in chronic diseases

Chronic or non-communicable diseases are the leading cause of death worldwide; they usually result in long-term illnesses and demand long-term care. Despite advances in molecular therapeutics, specific biomarkers and targets for the treatment of these diseases are required. The dysregulation of de novo lipogenesis has been found to play an essential role in cell metabolism and is associated with the development and progression of many chronic diseases; this confirms the link between obesity and various chronic diseases. The main enzyme in this pathway-ATP-citrate lyase (ACLY), a lipogenic enzyme-catalyzes the critical reaction linking cellular glucose catabolism and lipogenesis. Increasing lines of evidence suggest that the modulation of ACLY expression correlates with the development and progressions of various chronic diseases such as neurodegenerative diseases, cardiovascular diseases, diabetes, obesity, inflammation, and cancer. Recent studies suggest that the inhibition of ACLY activity modulates the glycolysis and lipogenesis processes and stimulates normal physiological functions. This comprehensive review aimed to critically evaluate the role of ACLY in the development and progression of different diseases and the effects of its downregulation in the prevention and treatment of these diseases.

Benzyl butyl phthalate (BBP) triggers the malignancy of acute myeloid leukemia cells via upregulation of PDK4

Acute Myeloid Leukemia (AML) is a cancer of hematopoietic stem cells with a rapid progression. Recent studies indicated that endocrine disruptor chemicals (EDCs) are potential risk factors for AML progression. Our present data showed that an industrial endocrine disrupting chemical, Benzyl butyl phthalate (BBP), can promote the proliferation of AML cells and decrease their sensitivity to daunorubicin (DNR) and cytarabine (Ara-C) treatments. Further, BBP can increase the glucose consumption, lactate generation, and ATP levels of AML cells. Among the measured glycolysis-related genes, BBP can increase the expression of pyruvate dehydrogenase lipoamide kinase isozyme 4 (PDK4), a mitochondrial protein that regulates the tricarboxylic acid cycle (TCA) cycle. The inhibitor of PDK4 or its specific siRNA can attenuate BBP-induced cell proliferation and ATP generation, which suggested the essential roles of PDK4 in BBP-induced glycolysis and proliferation. Further, BBP can increase the mRNA stability of PDK4, while had no effect on its transcription and protein stability. miR-15b-5p can bind with the 3'UTR of PDK4 to decrease its mRNA stability, while BBP can decrease the expression of miR-15b-5p in AML cells. Collectively, our data showed that BBP can trigger the malignancy of AML cells via regulation of miR-15b-5p/PDK4 signals.

Dichloroacetate restores colorectal cancer chemosensitivity through the p53/miR-149-3p/PDK2-mediated glucose metabolic pathway

The development of chemoresistance remains a major challenge that accounts for colorectal cancer (CRC) lethality. Dichloroacetate (DCA) was originally used as a metabolic regulator in the treatment of metabolic diseases; here, DCA was assayed to identify the mechanisms underlying the chemoresistance of CRC. We found that DCA markedly enhanced chemosensitivity of CRC cells to fluorouracil (5-FU), and reduced the colony formation due to high levels of apoptosis. Using the microarray assay, we noted that miR-149-3p was involved in the chemoresistance of CRC, which was modulated by wild-type p53 after DCA treatment. In addition, PDK2 was identified as a direct target of miR-149-3p. Mechanistic analyses showed that overexpression of miR-149-3p enhanced 5-FU-induced apoptosis and reduced glucose metabolism, similar to the effects of PDK2 knockdown. In addition, overexpression of PDK2 partially reversed the inhibitory effect of miR-149-3p on glucose metabolism. Finally, both DCA treatment and miR-149-3p overexpression in 5-FU-resistant CRC cells were found to markedly sensitize the chemotherapeutic effect of 5-FU in vivo, and this effect was also validated in a small retrospective cohort of CRC patients. Taken together, we determined that the p53/miR-149-3p/PDK2 signaling pathway can potentially be targeted with DCA treatment to overcome chemoresistant CRC.

Metabolic Flexibility in Cancer: Targeting the Pyruvate Dehydrogenase Kinase:Pyruvate Dehydrogenase Axis

Cancer cells use alterations of normal metabolic processes to sustain proliferation indefinitely. Transcriptional and posttranscriptional control of the pyruvate dehydrogenase kinase (PDK) family is one way in which cancer cells alter normal pyruvate metabolism to fuel proliferation. PDKs can phosphorylate and inactivate the pyruvate dehydrogenase complex (PDHC), which blocks oxidative metabolism of pyruvate by the mitochondria. This process is thought to enhance cancer cell growth by promoting anabolic pathways. Inhibition of PDKs induces cell death through increased PDH activity and subsequent increases in ROS production. The use of PDK inhibitors has seen widespread success as a potential therapeutic in laboratory models of multiple cancers; however, gaps still exist in our understanding of the biology of PDK regulation and function, especially in the context of individual PDKs. Efforts are currently underway to generate PDK-specific inhibitors and delineate the roles of individual PDK isozymes in specific cancers. The goal of this review is to understand the regulation of the PDK isozyme family, their role in cancer proliferation, and how to target this pathway therapeutically to specifically and effectively reduce cancer growth.

Circular RNA circCRIM1 inhibits invasion and metastasis in lung adenocarcinoma through the microRNA (miR)-182/miR-93-leukemia inhibitory factor receptor pathway

In recent years, circular RNAs (circRNAs) have been revealed to have important roles in carcinogenesis. Metastasis is the leading cause of lung adenocarcinoma (LUAC) death. However, the contributions of circRNA to the metastasis of LUAC remain largely unknown. Based on circBase data and our biobank tissues, we identified circCRIM1 (a circRNA derived from exons 2, 3 and 4 of the CRIM1 gene, hsa_circ_0002346) as having a significantly decreased expression in LUAC samples compared with matched normal control samples. Both in vivo and in vitro experiments revealed that circCRIM1 suppresses the invasion and metastasis of LUAC. In vitro precipitation of circRNAs, luciferase reporter assay, and biotin‐coupled microRNA capture were carried out to investigate the Ago2‐dependent interaction of circCRIM1 and microRNA (miR)‐93/miR‐182. Mechanistically, we found that circCRIM1 could promote the expression of leukemia inhibitory factor receptor, a well‐known tumor suppressor, by sponging miR‐93 and miR‐182. In the clinical and pathological analyses, the downregulation of circCRIM1 in LUAC was significantly correlated with lymphatic metastasis and TNM stage, which served as an independent risk factor for the overall survival of patients with LUAC. Our study showed that circCRIM1 inhibits the invasion and metastasis of lung adenocarcinoma cancer cells, which makes it a potential therapeutic target.

Non-coding RNAs derailed: The many influences on the fatty acid reprogramming of cancer

Non-coding RNAs (NcRNAs), a family of functional RNA molecules that cannot translate into proteins but control specific gene expression programs, have been shown to be implicated in various biological processes, including fatty acid metabolism. Fast-growing tumor cells rewire their fatty acid metabolic circuitry in order to meet the needs of energy storage, membrane proliferation, and the generation of signaling molecules, which is achieved by regulating a variety of key enzymes along with related signaling pathways in fatty acid metabolism. This review presents an update of our knowledge about the regulatory network of ncRNAs-specifically, microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs)-in this metabolic shift and discusses the possibility of ncRNA-based therapeutics being applied to the restoration of cancer-related fatty acid metabolism.

Emergence of MicroRNAs as Key Players in Cancer Cell Metabolism

BACKGROUND

Metabolic reprogramming is a hallmark of cancer. MicroRNAs (miRNAs) have been found to regulate cancer metabolism by regulating genes involved in metabolic pathways. Understanding this layer of complexity could lead to the development of novel therapeutic approaches.

CONTENT

miRNAs are noncoding RNAs that have been implicated as master regulators of gene expression. Studies have revealed the role of miRNAs in the metabolic reprogramming of tumor cells, with several miRNAs both positively and negatively regulating multiple metabolic genes. The tricarboxylic acid (TCA) cycle, aerobic glycolysis, de novo fatty acid synthesis, and altered autophagy allow tumor cells to survive under adverse conditions. In addition, major signaling molecules, hypoxia-inducible factor, phosphatidylinositol-3 kinase/protein kinase B/mammalian target of rapamycin/phosphatase and tensin homolog, and insulin signaling pathways facilitate metabolic adaptation in tumor cells and are all regulated by miRNAs. Accumulating evidence suggests that miRNA mimics or inhibitors could be used to modulate the activity of miRNAs that drive tumor progression via altering their metabolism. Currently, several clinical trials investigating the role of miRNA-based therapy for cancer have been launched that may lead to novel therapeutic interventions in the future.

SUMMARY

In this review, we summarize cancer-related metabolic pathways, including glycolysis, TCA cycle, pentose phosphate pathway, fatty acid metabolism, amino acid metabolism, and other metabolism-related oncogenic signaling pathways, and their regulation by miRNAs that are known to lead to tumorigenesis. Further, we discuss the current state of miRNA therapeutics in the clinic and their future potential.