Mitochondrial pyruvate carrier function determines cell stemness and metabolic reprogramming in cancer cells.

One of the remarkable features of cancer cells is aerobic glycolysis, a phenomenon known as the "Warburg Effect", in which cells rely preferentially on glycolysis instead of oxidative phosphorylation (OXPHOS) as the main energy source even in the presence of high oxygen tension. Cells with dysfunctional mitochondria are unable to generate sufficient ATP from mitochondrial OXPHOS, and then are forced to rely on glycolysis for ATP generation. Here we report our results in a prostate cancer cell line in which the mitochondrial pyruvate carrier 1 (MPC1) gene was knockout. It was discovered that the MPC1 gene knockout cells revealed a metabolism reprogramming to aerobic glycolysis with reduced ATP production, and the cells became more migratory and resistant to both chemotherapy and radiotherapy. In addition, the MPC1 knockout cells expressed significantly higher levels of the stemness markers Nanog, Hif1α, Notch1, CD44 and ALDH. To further verify the correlation of MPC gene function and cell stemness/metabolic reprogramming, MPC inhibitor UK5099 was applied in two ovarian cancer cell lines and similar results were obtained. Taken together, our results reveal that functional MPC may determine the fate of metabolic program and the stemness status of cancer cells in vitro.

Pyruvate dehydrogenase expression is negatively associated with cell stemness and worse clinical outcome in prostate cancers.

Cells generate adenosine-5'-triphosphate (ATP), the major currency for energy-consuming reactions, through mitochondrial oxidative phosphorylation (OXPHOS) and glycolysis. One of the remarkable features of cancer cells is aerobic glycolysis, also known as the "Warburg Effect", in which cancer cells rely preferentially on glycolysis instead of mitochondrial OXPHOS as the main energy source even in the presence of high oxygen tension. One of the main players in controlling OXPHOS is the mitochondrial gatekeeperpyruvate dehydrogenase complex (PDHc) and its major subunit is E1α (PDHA1). To further analyze the function of PDHA1 in cancer cells, it was knock out (KO) in the human prostate cancer cell line LnCap and a stable KO cell line was established. We demonstrated that PDHA1 gene KO significantly decreased mitochondrial OXPHOS and promoted anaerobic glycolysis, accompanied with higher stemness phenotype including resistance to chemotherapy, enhanced migration ability and increased expression of cancer stem cell markers. We also examined PDHA1 protein expression in prostate cancer tissues by immunohistochemistry and observed that reduced PDHA1 protein expression in clinical prostate carcinomas was significantly correlated with poor prognosis. Collectively, our results show that negative PDHA1 gene expressionis associated with significantly higher cell stemness in prostate cancer cells and reduced protein expression of this gene is associated with shorter clinical outcome in prostate cancers.

MPC1 and MPC2 expressions are associated with favorable clinical outcomes in prostate cancer.

BACKGROUND: Cancer cells exhibit an altered metabolism, which is characterized by a preference for aerobic glycolysis more than mitochondrial oxidation of pyruvate. Mitochondrial pyruvate carrier 1 (MPC1) and mitochondrial pyruvate carrier 2 (MPC2) play a bottleneck role by transporting pyruvate into mitochondrial through the mitochondrial inner membrane. Therefore, their protein expression in cancers may be of clinical consequences. There are studies showing low levels of MPC1 expression in colon, kidney and lung cancers, and the expression of MPC1 correlates with poor prognosis. However, the expression status of MPC1 and MPC2 in prostate cancer (PCA) is unclear. METHODS: In this study, expression of MPC1 and MPC2 in LNCaP and DU145 prostate cancer cell lines was examined by immunocytochemistry (ICC) and Western blotting. Compared to the LNCaP cells, lower levels of MPC1 and MPC2 expression in the DU145 cell line was identified. We then extended our study to 88 patients with prostate cancer who underwent transurethral electro-vaporization of prostate or radical prostatectomy at the First Affiliated Hospital of Zhengzhou University, Henan, China. Patient-derived paraffin embedded PCA specimens were collected for immunohistochemistry (IHC). Correlations with clinicopathologic factors were evaluated by Chi-square or Fisher´s exact probability tests. Overall survival (OS) rates were determined using the Kaplan-Meier estimator. The Cox proportional hazard regression model was used in univariate analysis and multivariate analysis to identify factors significantly correlated with prognosis. RESULTS: Linear regression analysis revealed that MPC1 expression level was positively correlated with MPC2 expression (r = 0.375, P = 0.006) in the prostate cancers. MPC1 expression was negatively associated with UICC stage (P = 0.031). While UICC stage (P < 0.001) and lymph node metastasis (P = 0.002) were negatively associated with MPC2 expression. Positive MPC1 or MPC2 expression in cancer tissues was significantly associated with higher OS (P < 0.05). The multivariate analysis showed that both MPC1 and MPC2 expressions in PCA were independent prognostic factors for higher OS (For MPC1: RR = 0.654, 95% CI: 0.621-0690, P < 0.001; For MPC2: RR = 0.696, 95% CI: 0.660-0.734, P < 0.001). CONCLUSIONS: Our study indicates that MPC1 and MPC2 expressions are of prognostic values in PCAs and that positive expression of MPC1 or MPC2 is a predictor of favorable outcome.

Establishment of mitochondrial pyruvate carrier 1 (MPC1) gene knockout mice with preliminary gene function analyses.

Pyruvate plays a critical role in the mitochondrial tricarboxylic acid (TCA) cycle, and it is the center product for the synthesis of amino acids, carbohydrates and fatty acids. Pyruvate transported across the inner mitochondrial membrane appears to be essential in anabolic and catabolic intermediary metabolism. The mitochondrial pyruvate carrier (MPC) mounted in the inner membrane of mitochondria serves as the channel to facilitate pyruvate permeating. In mammals, the MPC is formed by two paralogous subunits, MPC1 and MPC2. It is known that complete ablation of MPC2 in mice causes death on the 11th or 12th day of the embryonic period. However, MPC1 deletion and the knowledge of gene function in vivo are lacking. Using the new technology of gene manipulation known as Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-associated 9 (CRISPR/Cas9) systems, we gained stable MPC1 gene heterozygous mutation mice models, and the heterozygous mutations could be stably maintained in their offsprings. Only one line with homozygous 27 bases deletion in the first exon was established, but no offsprings could be obtained after four months of mating experiments, indicating infertility of the mice with such homozygous deletion. The other line of MPC1 knockout (KO) mice was only heterozygous, which mutated in the first exon with a terminator shortly afterwards. These two lines of MPC1 KO mice showed lower fertility and significantly higher bodyweight in the females. We concluded that heterozygous MPC1 KO weakens fertility and influences the metabolism of glucose and fatty acid and bodyweight in mice.

PDHA1 gene knockout in prostate cancer cells results in metabolic reprogramming towards greater glutamine dependence.

Alternative pathways of metabolism endowed cancer cells with metabolic stress. Inhibiting the related compensatory pathways might achieve synergistic anticancer results. This study demonstrated that pyruvate dehydrogenase E1α gene knockout (PDHA1 KO) resulted in alterations in tumor cell metabolism by rendering the cells with increased expression of glutaminase1 (GLS1) and glutamate dehydrogenase1 (GLUD1), leading to an increase in glutamine-dependent cell survival. Deprivation of glutamine induced cell growth inhibition, increased reactive oxygen species and decreased ATP production. Pharmacological blockade of the glutaminolysis pathway resulted in massive tumor cells apoptosis and dysfunction of ROS scavenge in the LNCaP PDHA1 KO cells. Further examination of the key glutaminolysis enzymes in human prostate cancer samples also revealed that higher levels of GLS1 and GLUD1 expression were significantly associated with aggressive clinicopathological features and poor clinical outcome. These insights supply evidence that glutaminolysis plays a compensatory role for cell survival upon alternative energy metabolism and targeting the glutamine anaplerosis of energy metabolism via GLS1 and GLUD1 in cancer cells may offer a potential novel therapeutic strategy.

Aldehyde Dehydrogenase-1 Expression Predicts Unfavorable Outcomes in Patients with Esophageal Squamous Cell Carcinoma.

BACKGROUND: Aldehyde dehydrogenase-1 (ALDH1) has been shown to be a potential cancer stem cell marker in different types of cancer. However, the role of its expression in tumor cells and the microenvironment in different types of cancer is still controversial. MATERIALS AND METHODS: ALDH1 protein was immunohistochemically investigated and analyzed in 157 samples of surgically dissected esophageal squamous cell carcinoma (ESCC) tissues. RESULTS: ALDH1 protein expression in ESCC tumor cells was significantly associated with poor differentiation (p<0.05) and strongly positive ALDH1 expression in tumor cells was related with shorter overall survival (p<0.05), while the expression of ALDH1 in ESCC stromal cells had no significant relationship with clinicopathological features (p>0.05). CONCLUSION: High expression of cancer stem cell marker ALDH1 in ESCC cells may thus portend a poor prognosis. However, its expression in the tumor microenvironment did not appear to have a role in ESCC behavior. More studies are warranted to find out the mechanisms to explain this.