Benserazide is a novel inhibitor targeting PKM2 for melanoma treatment

The M2 splice isoform of pyruvate kinase (PKM2) is a key enzyme for generating pyruvate and ATP in the glycolytic pathway, whereas the role of PKM2 in tumorigenesis remains a subject of debate. In our study, we found PKM2 is highly expressed in melanoma patients and the malignance is positively correlated with high PKM2 activity and glycolytic capability in melanoma cells. Suppression of PKM2 expression by knocking down markedly attenuated malignant phenotype both in vitro and in vivo, and restoration of PKM2 expression in PKM2 depleted cells could rescue melanoma cells proliferation, invasion and metastasis. With the data indicating PKM2 as a potential therapeutic target, we performed screening for PKM2 inhibitors and identified benserazide (Ben), a drug currently in clinical use. We demonstrated that Ben directly binds to and blocks PKM2 enzyme activity, leading to inhibition of aerobic glycolysis concurrent up-regulation of OXPHOS. Of note, despite PKM2 is very similar to PKM1, Ben does not affect PKM1 enzyme activity. We showed that Ben significantly inhibits cell proliferation, colony formation, invasion and migration in vitro and in vivo. The specificity of Ben was demonstrated by the findings that, suppression of PKM2 expression diminishes the efficacy of Ben in inhibition of melanoma cell growth; ectopic PKM2 expression in normal cells sensitizes cells to Ben treatment. Interestingly, PKM2 activity and aerobic glycolysis are upregulated in BRAFi-resistant melanoma cells. As a result, BRAFi-resistant cells exhibit heightened sensitivity to suppression of PKM2 expression or treatment with Ben both in vitro and in vivo.     

Co-expression of PKM2 and TRIM35 predicts survival and recurrence in hepatocellular carcinoma

The identification of prognostic markers for hepatocellular carcinoma (HCC) is needed for clinical practice. Tripartite motif-containing 35 (TRIM35) is a tumor suppressor of HCC. TRIM35 inhibits phosphorylation of pyruvate kinase isoform M2 (PKM2), which is involved in aerobic glycolysis of cancer cells. We found that expression of PKM2 was significantly increased in HCC tissues. This overexpression of PKM2 was correlated with a high TNM stage and level of vascular invasion. Patients with HCC who were positive for PKM2 expression and negative for TRIM35 expression had shorter overall survival and time to recurrence than patients who were negative for PKM2 and positive for TRIM35. Furthermore, PKM2/TRIM35 combination was an independent and significant risk factor for recurrence and survival. In conclusion, PKM2 (+) and TRIM35 (−) contribute to the aggressiveness and poor prognosis of HCC. PKM2/TRIM35 expression could be a biomarker for the prognosis of HCC and target for cancer therapy.     

PKM2蛋白在胃癌组织中的表达及其预后价值

目的 探讨M2型丙酮酸激酶（PKM2）在人胃癌组织中的表达,并分析其与胃癌临床病理特征的关系及预后价值。方法 构建含202例胃癌组织及其对应癌旁组织的组织芯片,采用免疫组化法检测胃癌组织中PKM2蛋白的表达,分析其阳性表达与临床病理参数和预后间的关系。结果PKM2在胃癌组织中的阳性表达率为62.4％（126／202）,高于癌旁组织的14.4％（29／202）,差异有统计学意义（P＜0.05）;胃癌组织中PKM2的阳性表达率与年龄、性别、肿瘤最大直径及分化程度均无关（P＞0.05）,与T分期、N分期及TNM分期有关,差异有统计学意义（P＜0.05）。PKM2表达阳性者的中位总生存期为42.9个月,短于阴性表达者的78.4个月（χ2=23.119, P＜0.001）,且PKM2阳性表达情况是影响胃癌预后的独立因素之一。结论PKM2蛋白在胃癌的发生和发展过程中起了重要作用,是评估胃癌患者预后的重要因素。     

Enhancing mitochondrial respiration suppresses tumor promoter TPA-induced PKM2 expression and cell transformation in skin epidermal JB6 cells

Differentiated cells primarily metabolize glucose for energy via the tricarboxylic acid cycle and oxidative phosphorylation, but cancer cells thrive on a different mechanism to produce energy, characterized as the Warburg effect, which describes the increased dependence on aerobic glycolysis. The M2 isoform of pyruvate kinase (PKM2), which is responsible for catalyzing the final step of aerobic glycolysis, is highly expressed in cancer cells and may contribute to the Warburg effect. However, whether PKM2 plays a contributing role during early cancer development is unclear. In our studies, we have made an attempt to elucidate the effects of varying mitochondrial respiration substrates on skin cell transformation and expression of PKM2. Tumorigenicity in murine skin epidermal JB6 P+ (promotable) cells was measured in a soft agar assay using 12-O-tetradecanoylphorbol-13-acetate (TPA) as a tumor promoter. We observed a significant reduction in cell transformation upon pretreatment with the mitochondrial respiration substrate succinate or malate/pyruvate. We observed that increased expression and activity of PKM2 in TPA-treated JB6 P+ cells and pretreatment with succinate or malate/pyruvate suppressed the effects. In addition, TPA treatment also induced PKM2 whereas PKM1 expression was suppressed in mouse skin epidermal tissues in vivo. In comparison with JB6 P+ cells, the nonpromotable JB6 P- cells showed no increase in PKM2 expression or activity upon TPA treatment. Knockdown of PKM2 using a siRNA approach significantly reduced skin cell transformation. Thus, our results suggest that PKM2 activation could be an early event and play a contributing role in skin tumorigenesis.     

Pyruvate kinase expression (PKM1 and PKM2) in cancer-associated fibroblasts drives stromal nutrient production and tumor growth

We have previously demonstrated that enhanced aerobic glycolysis and/or autophagy in the tumor stroma supports epithelial cancer cell growth and aggressive behavior, via the secretion of high-energy metabolites. These nutrients include lactate and ketones, as well as chemical building blocks, such as amino acids (glutamine) and nucleotides. Lactate and ketones serve as fuel for cancer cell oxidative metabolism, and building blocks sustain the anabolic needs of rapidly proliferating cancer cells. We have termed these novel concepts the “Reverse Warburg Effect,” and the “Autophagic Tumor Stroma Model of Cancer Metabolism.” We have also identified a loss of stromal caveolin-1 (Cav-1) as a marker of stromal glycolysis and autophagy. The aim of the current study was to provide genetic evidence that enhanced glycolysis in stromal cells favors tumorigenesis. To this end, normal human fibroblasts were genetically-engineered to express the two isoforms of pyruvate kinase M (PKM1 and PKM2), a key enzyme in the glycolytic pathway. In a xenograft model, fibroblasts expressing PKM1 or PKM2 greatly promoted the growth of co-injected MDA-MB-231 breast cancer cells, without an increase in tumor angiogenesis. Interestingly, PKM1 and PKM2 promoted tumorigenesis by different mechanism(s). Expression of PKM1 enhanced the glycolytic power of stromal cells, with increased output of lactate. Analysis of tumor xenografts demonstrated that PKM1 fibroblasts greatly induced tumor inflammation, as judged by CD45 staining. In contrast, PKM2 did not lead to lactate accumulation, but triggered a “pseudo-starvation” response in stromal cells, with induction of an NFκB-dependent autophagic program, and increased output of the ketone body 3- hydroxy-buryrate. Strikingly, in situ evaluation of Complex IV activity in the tumor xenografts demonstrated that stromal PKM2 expression drives mitochondrial respiration specifically in tumor cells. Finally, immuno-histochemistry analysis of human breast cancer samples lacking stromal Cav-1 revealed PKM1 and PKM2 expression in the tumor stroma. Thus, our data indicate that a subset of human breast cancer patients with a loss of stromal Cav-1 show profound metabolic changes in the tumor microenvironment. As such, this subgroup of patients may benefit therapeutically from potent inhibitors targeting glycolysis, autophagy and/or mitochondrial activity (such as metformin).     

Deubiquitinase PSMD14 promotes ovarian cancer progression by decreasing enzymatic activity of PKM2

Dysregulation of deubiquitination has been reported to contribute to carcinogenesis. However, the function and mechanism of deubiquitinating enzyme 26S proteasome non‐ATPase regulatory subunit 14 (PSMD14) in the progression of ovarian cancer (OV), the deadliest gynecological cancer, still remains to be characterized. The present study demonstrated that PSMD14 was overexpressed in OV tissues and its higher levels correlated with a higher International Federation of Gynecology and Obstetrics (FIGO) stage in OV patients. A high level of PSMD14 expression was related to poor survival in OV patients. Knockdown and overexpression experiments elucidated that PSMD14 stimulated OV cell proliferation, invasion, and migration in vitro. Repression of PSMD14 suppressed OV tumor growth in vivo. PSMD14 inhibitor O‐phenanthroline (OPA) effectively attenuated malignant behaviors of OV cells in vitro and OV tumor growth in vivo. Mechanistically, we uncovered that PSMD14 was involved in post‐translational regulation of pyruvate kinase M2 isoform (PKM2). PSMD14 decreased K63‐linked ubiquitination on PKM2, downregulated the ratio of PKM2 tetramers to dimers and monomers, and subsequently diminished pyruvate kinase activity and induced nuclear translocation of PKM2, contributing to aerobic glycolysis in OV cells. Collectively, our findings highlight the potential roles of PSMD14 as a biomarker and therapeutic candidate for OV.     

MiR‐133b inhibits growth of human gastric cancer cells by silencing pyruvate kinase muscle‐splicer polypyrimidine tract‐binding protein 1

The metabolism in tumor cells shifts from oxidative phosphorylation to glycolysis even in an aerobic environment. This phenomenon is known as the Warburg effect. This effect is regulated mainly by polypyrimidine tract‐binding protein 1 (PTBP1), which is a splicer of the mRNA for the rate‐limiting enzymes of glycolysis, pyruvate kinase muscle 1 and 2 (PKM1 and PKM2). In the present study, we demonstrated that miR‐133b reduced PTBP1 expression at translational level and that the expression levels of miR‐133b were significantly downregulated in gastric cancer clinical samples and human cell lines, whereas the protein expression level of PTBP1 was upregulated in 80% of the 20 clinical samples of gastric cancer examined. Ectopic expression of miR‐133b and knockdown of PTBP1 in gastric cancer cells inhibited cell proliferation through the induction of autophagy by the switching of PKM isoform expression from PKM2‐dominant to PKM1‐dominant. The growth inhibition was partially canceled by an autophagy inhibitor 3‐MA or a reactive oxygen species scavenger N‐acetylcysteine. These findings indicated that miR‐133b acted as a tumor‐suppressor through negative regulation of the Warburg effect in gastric cancer cells.     

GLUT1和PKM2在二甲双胍抑制人乳头状甲状腺癌细胞增殖中的作用

目的:观察不同浓度二甲双胍对人乳头状甲状腺癌（papillary thyroid cancer,PTC）细胞增殖、凋亡的影响,检测细胞中葡萄糖转运关键蛋白—葡萄糖转运体1（GLUT1）和糖酵解关键酶—M2型丙酮酸激酶（PKM2）表达水平的变化。方法:体外培养人PTC细胞BCPAP和K1,分为对照组和不同浓度二甲双胍（1、5和10mmol/L）处理组,并分别培养24h、48h和72h。四甲基偶氮唑蓝（MTT）法检测细胞增殖,Annexin V-FITC/PI流式细胞术检测细胞凋亡,实时定量PCR检测GLUT1和PKM2 mRNA的表达,Western blot检测GLUT1和PKM2蛋白的表达。结果:与对照组相比,二甲双胍抑制PTC细胞增殖,随浓度及处理时间的增加,抑制效应加大,呈剂量-时间依赖性（P<0.05）。二甲双胍诱导PTC细胞凋亡,随浓度及处理时间的增加,其中晚期凋亡率明显增加,呈剂量-时间依赖性（P<0.05）。二甲双胍可抑制PTC细胞中GLUT1和PKM2 mRNA的表达水平,呈剂量-时间依赖性（P<0.05）。二甲双胍可抑制PTC细胞中GLUT1和PKM2蛋白的表达水平,呈时间依赖性。结论:二甲双胍抑制人PTC细胞增殖并诱导凋亡,其机制之一可能是抑制葡萄糖转运关键蛋白和糖酵解关键酶的表达,负面影响癌细胞生长的能量供应。     

沉默PKM2对人肺腺癌细胞系及移植瘤的放射增敏研究

目的 研究沉默丙酮酸激酶M2型(PKM2)对人肺腺癌细胞系(A549细胞)的放射敏感性及移植瘤的放射协同作用,并探索相关机制。方法 将PKM2基因干扰质粒pshRNA-PKM2稳定转染至A549细胞,同时设立空载质粒转染组和未转染组。采用蛋白印迹法检测A549细胞pshRNA-PKM2的沉默效率及微管相关蛋白1轻链3(LC3)表达水平,克隆形成实验、移植瘤生长延迟法检测沉默PKM2后对A549细胞、移植瘤放射增敏效应,透射电镜观察A549细胞及移植瘤自噬形成,免疫组化法检测移植瘤中PKM2的表达水平。行Student′s t检验组间差异,裸鼠体重及移植瘤体积采用连续变量的方差分析。结果 成功获得转染pshRNA-PKM2的A549稳定细胞株。pshRNA-PKM2组可显著下调细胞和移植瘤PKM2的蛋白表达水平(P=0.001、0.000),对A549细胞的SER为1.47,移植瘤的SER为2.00。干扰PKM2可增加放射所诱导的自噬形成并增加LC3-Ⅱ/Ⅰ的比值(P=0.0001)。结论 沉默PKM2调节自噬可能提高A549细胞及移植瘤的放射敏感性,其有望成为NSCLC有效放射增敏靶点,但有待进一步研究确认。     

PKM2在乳腺癌中的预后价值分析

目的 探讨乳腺癌患者中PKM2基因表达水平,并分析PKM2基因表达与乳腺癌预后的关系。方法 采用生物信息学方法,利用互联网平台和开放性的基于基因芯片检测的基因表达数据库,比较PKM2基因在乳腺癌组织与乳腺正常组织中的表达差异,分析PKM2表达水平与乳腺癌预后的关系。结果PKM2在乳腺癌中的表达水平明显高于正常乳腺组织（P＜0. 05）。PKM2表达与乳腺癌患者预后密切相关,PKM2高表达者的疾病特异性生存率显著低于低表达者（HR=1.897,95％CI：1.117～3.221, P＜0.05）,PKM2高表达者较PKM2低表达者具有较短的无病生存时间（HR=1.605,95％CI：1.050～2.451,P=0.029）和无复发生存时间（HR=7.377,95％CI：1.906～28.548, P=0.004）。结论 PKM2基因在乳腺癌组织中呈高表达,其表达水平对预测乳腺癌患者的预后具有重要意义。     

索拉菲尼抑制肿瘤细胞PKM2蛋白表达

目的:探讨索拉菲尼对肿瘤细胞中PKM2蛋白表达的影响。方法:以人肝癌细胞HepG2、人胆管癌细胞QBC939、人肺癌细胞NCI-H446、人宫颈癌细胞Hela为研究对象,体外培养上述肿瘤细胞;光镜下观察不同肿瘤细胞经不同浓度索拉菲尼处理后细胞形态学改变;CCK-8法检测索拉菲尼对上述肿瘤细胞增殖的影响。用Western blot 检测索拉菲尼对上述细胞的PKM2表达变化。结果:光镜下观察可见随着索拉菲尼浓度的增加,肿瘤细胞离巢、凋亡,并且随着浓度的增加而增加。细胞增殖实验可见,索拉菲尼显著抑制HepG2、QBC939、NCI-H446、Hela细胞的增殖,不同浓度（2.5 μmol/L、5.0 μmol/L、10.0 μmol/L、20.0 μmol/L）的索拉菲尼处理上述细胞48 h后,各药物处理组与对照组比较（P均<0.01）,呈剂量效应关系;索拉菲尼处理上述肿瘤细胞48 h的IC50分别为10.61 μmol/L、13.88 μmol/L、15.66 μmol/L、12.86 μmol/L。Western blot检测结果显示,不同浓度的索拉非尼显著抑制HepG2、QBC939、NCI-H446、Hela细胞的PKM2的蛋白表达,并且表达与浓度呈剂量关系。蛋白表达半定量分析可见,各肿瘤细胞经过索拉菲尼处理后与对照组比较,蛋白表达差异有统计学意义（P＜0.05）。结论:索拉菲尼能抑制人多种肿瘤细胞增殖并显著抑制PKM2蛋白表达。     

PKM2 siRNA对人甲状腺乳头状癌细胞生长和增殖的影响

目的：研究PKM2在甲状腺乳头状癌（PTC）中的表达特性及其在PTC中的作用。方法：用抗PKM2的小干扰RNA转染PTC细胞。Western blot和RT-PCR技术分析细胞中PKM2的表达。MTT法和细胞平板克隆形成实验评估细胞的生长和增殖。采用乳酸、ATP和葡萄糖试剂盒分别测定细胞代谢产生的乳酸、ATP及消耗的葡萄糖。结果：PKM2在PTC中异常高表达。在PTC细胞系中应用特异性抗PKM2 siRNA可延缓细胞生长并降低其克隆形成能力。PKM2 siRNA可降低PTC细胞乳酸、ATP的产生,减少葡萄糖的消耗。结论：PKM2高表达可通过激活糖酵解的方式使PTC细胞具有选择性生长优势。PKM2异常高表达可能作为新的生物标记物,并成为PTC的潜在治疗靶点。     

PKM2 promotes metastasis by recruiting myeloid-derived suppressor cells and indicates poor prognosis for hepatocellular carcinoma

Pyruvate kinase M2 (PKM2) is a member of the pyruvate kinase family. Recent work has defined the “non-metabolic” functions of PKM2. However, the role of PKM2 in HCC remains unclear. To investigate the role of PKM2 in tumor growth, invasion and the prognosis of hepatocellular carcinoma (HCC), PKM2 expression was measured in HCC cell lines and tissues using qRT-PCR, western blot, and immunofluorescence assays. In in vitro experiments, PKM2 was knocked down using a short hairpin RNA lentivirus vector, and tumor cell behavior and the downstream signaling pathways and chemokine were analyzed. For the analysis of in vivo tumor growth, intratumoral and peritumoral lymphocyte infiltration were examined in nude mice. The prognostic value of PKM2 was analyzed by immunohistochemistry in two cohorts including 721 HCC patients. Together, our data obtained from cell lines, tumorigenicity studies, and primary HCC samples illustrate an oncogenic role for PKM2 in tumors. Moreover, PKM2 may serve as a novel prognostic indicator for HCC patients after curative resection, targeted therapy aimed at PKM2 may represent an effective treatment approach for HCC.     

Turning on a fuel switch of cancer: hnRNP proteins regulate alternative splicing of pyruvate kinase mRNA

Unlike normal cells, which metabolize glucose by oxidative phosphorylation for efficient energy production, tumor cells preferentially metabolize glucose by aerobic glycolysis, which produces less energy but facilitates the incorporation of more glycolytic metabolites into the biomass needed for rapid proliferation. The metabolic shift from oxidative phosphorylation to aerobic glycolysis is partly achieved by a switch in the splice isoforms of the glycolytic enzyme pyruvate kinase. Although normal cells express the pyruvate kinase M1 isoform (PKM1), tumor cells predominantly express the M2 isoform (PKM2). Switching from PKM1 to PKM2 promotes aerobic glycolysis and provides a selective advantage for tumor formation. The PKM1/M2 isoforms are generated through alternative splicing of two mutually exclusive exons. A recent study shows that the alternative splicing event is controlled by heterogeneous nuclear ribonucleoprotein (hnRNP) family members hnRNPA1, hnRNPA2, and polypyrimidine tract binding protein (PTB; also known as hnRNPI). These findings not only provide additional evidence that alternative splicing plays an important role in tumorigenesis, but also shed light on the molecular mechanism by which hnRNP proteins regulate cell proliferation in cancer.     

PKM2对人胃癌细胞HMGB1释放的影响

目的:探讨M2型丙酮酸激酶(pyruvate kinase M2,PKM2)对胃癌细胞高迁移率族蛋白B-1(high mobility group box 1,HMGB1)释放的作用。方法:通过siRNA干扰抑制人胃癌BGC823细胞PKM2的表达,Western blot检测各组细胞PKM2蛋白的表达,以评价PKM2 siRNA的转染效率;CCK-8法检测各组细胞活力,分析干扰PKM2的表达对胃癌BGC823细胞增殖的影响;Western blot检测各组细胞HMGB1的表达以及ELISA检测各组细胞培养液HMGB1的水平,分析PKM2对胃癌BGC823细胞HMGB1的作用。结果:与空载体pU6组相比,PKM2 siRNA 组PKM2的表达显著降低(P＜0.01),表明siRNA有效地抑制胃癌BGC823细胞PKM2的表达;CCK-8结果显示,PKM2 siRNA 组细胞活力明显低于空载体pU6组(P＜0.001),表明干扰PKM2抑制胃癌BGC823细胞增殖;此外,PKM2 siRNA 组HMGB1的表达以及细胞外HMGB1的水平显著降低(P＜0.01),表明干扰PKM2抑制人胃癌BGC823细胞HMGB1的释放。结论:PKM2促进人胃癌BGC823细胞HMGB1的释放。     

Expression of the bcl-2 gene family in normal and malignant breast tissue: Low bax-α expression in tumor cells correlates with resistance towards apoptosis

We have studied the expression of the apoptosis-regulating genes bcl-2, bcl-x, bax and APO-1/fas (CD95) in human breast cancer. The expression pattern of these genes in human breast-cancer tissues and breast-cancer-derived cell lines was compared to that seen in normal breast epithelium and breast epithelial cell lines. No difference with regard to bcl-2 and bcl-x_L expression was observed between normal breast epithelium and tumor tissue or breast cancer and non-malignant epithelial cell lines. In contrast, bax-α, a splice variant of bax, which promotes apoptosis, is expressed in high amounts in normal cell lines and breast tissue, whereas only weak or no expression could be detected in cancer-cell lines and malignant tissue. In contrast to malignant cell lines, which express low levels of bax-α, non-malignant epithelial cell lines displaying high amounts of bax-α were highly sensitive to induction of programmed cell death by both serum starvation and APO-1/fas (CD95) triggering. We therefore propose that dysregulation of apoptosis contributes to the pathogenesis of breast cancer, at least in part, due to an imbalance between anti-apoptosis genes (such as bcl-2/bcl-x) and apoptosis-promoting genes (bax).