Nobuhiko Sugito

MicroRNA-124 inhibits cancer cell growth through PTB1/PKM1/PKM2 feedback cascade in colorectal cancer

Altered levels and functions of microRNAs (miRs) have been associated with carcinogenesis. In this study, we investigated the role of miR-124 in colorectal adenoma (CRA) and cancer (CRC). The expression levels of miR-124 were decreased in CRA (81.8%) and CRC (57.6%) in 55 clinical samples. The ectopic expression of miR-124 induced apoptosis and autophagy in colon cancer cells. Also, miR-124 targeted polypyrimidine tract-binding protein 1 (PTB1), which is a splicer of pyruvate kinase muscles 1 and 2 (PKM1 and PKM2) and induced the switching of PKM isoform expression from PKM2 to PKM1. Also, siR-PTB1 induced drastic apoptosis in colon cancer cells. Furthermore, we found that the ectopic expression of miR-124 enhanced oxidative stress and the miR-124/PTB1/PKM1/PKM2 axis constituted a feedback cascade. Finally, we showed that intratumor injection of miR-124 and siR-PTB1 induced a tumor-suppressive effect in xenografted mice. The axis was established by both in vitro and in vivo experiments to function in human colorectal cancer cells. These findings suggest that miR-124 acts as a tumor-suppressor and a modulator of energy metabolism through a PTB1/PKM1/PKM2 feedback cascade in human colorectal tumor cells.

PTBP1-associated microRNA-1 and -133b suppress the Warburg effect in colorectal tumors

It is known that pyruvate kinase in muscle (PKM), which is a rate-limiting glycolytic enzyme, has essential roles in the Warburg effect and that expression of cancer-dominant PKM2 is increased by polypyrimidine tract-binding protein 1 (PTBP1), which is a splicer of the PKM gene. In other words, PKM2 acts as a promoter of the Warburg effect. Previously, we demonstrated that the Warburg effect was partially established by down-regulation of several microRNAs (miRs) that bind to PTBP1 and that ectopic expression of these miRs suppressed the Warburg effect. In this study, we investigated the functions of miR-1 and -133b, which are well known as muscle-specific miRs, from the viewpoint of the Warburg effect in colorectal tumors. The expression levels of miR-1 and -133b were relatively high in colon tissue except muscle and very frequently down-regulated in 75 clinical colorectal tumors samples, even in adenomas, compared with those of the adjacent normal tissue samples. The ectopic expression of these miRs induced growth suppression and autophagic cell death through the switching of PKM isoform expression from PKM2 to PKM1 by silencing PTBP1 expression both in vitro and in vivo. Also, we showed that the resultant increase in the intracellular level of reactive oxygen species (ROS) was involved in this mechanism. Furthermore, PTBP1 was highly expressed in most of the 30 clinical colorectal tumor samples examined, even in adenomas. Our results suggested that PTBP1 and PTBP1-associated miR-1 and -133b are crucial molecules for the maintenance of the Warburg effect in colorectal tumors.

Positive feedback of DDX6/c-Myc/PTB1 regulated by miR-124 contributes to maintenance of the Warburg effect in colon cancer cells

The human DEAD/H-box RNA helicase gene DDX6 is a target of the t(11;14)(q23;q32) chromosomal translocation observed in human B-cell lymphoma, and the overexpression of its protein has been shown to cause malignant transformation. DDX6 has a variety of functions such as translation initiation, pre-mRNA splicing, ribosome assembly, and more. However, details of the regulatory mechanism of DDX6 and functions of DDX6 in cancer cells are largely unknown. On the other hand, the Warburg effect is a well-known feature of cancer cells. Pyruvate kinase in muscle (PKM), which is a rate-limiting glycolytic enzyme, has 2 isoforms, PKM1 and PKM2. It has been frequently reported that PKM2 is a tumor-specific isoform and promotes the Warburg effect. However, the functions of the PKM1 gene have been hardly mentioned. Here, we showed that DDX6 was overexpressed in colorectal cancer specimens and regulated by microRNA (miR)-124 in colon cancer cells. Also, a DDX6/c-Myc/PTB1 positive feedback circuit regulated by miR-124 was shown to be established and to contribute to maintenance of the Warburg effect. Moreover, we showed that knockdown of DDX6 induced mainly apoptosis through an imbalance of PKM gene expression, especially causing down-regulation of PKM1 in colon cancer cells. These results suggest that miR-124 is a fine tuner of the Warburg effect and that DDX6 is one of the key molecules in Warburg effect-related miR-124 targeting various genes.

MicroRNA-214 and MicroRNA-126 Are Potential Biomarkers for Malignant Endothelial Proliferative Diseases

Malignant endothelial proliferative diseases including human angiosarcoma (AS) and canine hemangiosarcoma (HSA) are serious diseases with a grave prognosis. Establishing liquid biopsy-based biomarkers for screening has definite clinical utility; however, plasma miRNAs up- or down-regulated in these sarcomas have been unclear. For identifying possible diagnostic plasma miRNAs for these sarcomas, we investigated whether plasma miR-214 and miR-126, which miRNAs play important roles in angiogenesis and tumorigenesis, were elevated in malignant endothelial proliferative diseases. For this investigation, human angiosarcoma and canine hemangiosarcoma cell lines and clinical plasma samples of canine hemangiosarcoma were examined by performing miRNA qRT-PCR. We report here that human angiosarcoma and canine hemangiosarcoma cell lines over-secreted miR-214 and miR-126 via microvesicles; in addition, their levels in the plasma samples from canines with hemangiosarcoma were increased. Moreover, the surgical resection of primary tumors decreased the levels of plasma miR-214 and miR-126. Our findings suggest that these malignant endothelial proliferative diseases over-secreted miR-214 and miR-126, thus suggesting that these miRNAs have potential as diagnostic biomarkers for malignant endothelial proliferative diseases in canine and possible in human angiosarcoma.

MiR-145 negatively regulates Warburg effect by silencing KLF4 and PTBP1 in bladder cancer cells

The Warburg effect is a well-known feature in cancer-specific metabolism. We previously reported on the role of microRNA (miR)-145 as a tumor-suppressor in human bladder cancer (BC) cells. In this study, we reveal that miR-145 decreases the Warburg effect by silencing KLF4 in BC cells. The expression levels of miR-145 were significantly lower in clinical BC samples and BC cell lines compared to those in normal tissues and HUC cells. Luciferase assay results showed that miR-145 directly bound to 3′UTR of KLF4, which was shown to be overexpressed in the clinical BC samples using Western blot analysis and immunohistochemistry. Remarkable growth inhibition and apoptosis were induced by the ectopic expression of miR-145 or by the gene silencing of KLF4 (siR-KLF4). Also, Warburg effect-related genes such as PTBP1/PKMs were regulated by the transfection of BC cells with miR-145 or siR-KLF4. These results thus indicate that the miR-145/KLF4/PTBP1/PKMs axis is one of the critical pathways that maintain the Warburg effect in BC carcinogenesis. MiR-145 perturbed the Warburg effect by suppressing the KLF4/PTBP1/PKMs pathway in BC cells, resulting in significant cell growth inhibition.

Regulated Polarization of Tumor-Associated Macrophages by miR-145 via Colorectal Cancer–Derived Extracellular Vesicles

Macrophages are polarized into functional classically activated and alternatively activated (M2) phenotypes depending on their microenvironment, and these cells play an important role in the immune system. M2-like polarization of tumor-associated macrophages (TAMs) is activated by various secretions from cancer cells; however, the interaction between cancer cells and TAMs is not well understood. Recent studies showed that cancer cell–derived extracellular vesicles (EVs) contribute to tumor development and modulation of the tumor microenvironment. In the current study, we investigated colorectal cancer–derived EVs containing miR-145 with respect to the polarization of TAMs. Colorectal cancer cells positively secreted miR-145 via EVs, which were taken up by macrophage-like cells. Interestingly, colorectal cancer–derived EVs polarized macrophage-like cells into the M2-like phenotype through the downregulation of histone deacetylase 11. An in vivo study showed that EV-treated macrophages caused significant enlargement of the tumor volumes. These findings suggest that colorectal cancer cells use miR-145 within EVs to efficiently modulate M2-like macrophage polarization and tumor progression.

MicroRNA-214 Promotes Apoptosis in Canine Hemangiosarcoma by Targeting the COP1-p53 Axis

MicroRNA-214 regulates both angiogenic function in endothelial cells and apoptosis in various cancers. However, the regulation and function of miR-214 is unclear in canine hemangiosarcoma, which is a spontaneous model of human angiosarcoma. The expression and functional roles of miR-214 in canine hemangiosarcoma were presently explored by performing miRNA TaqMan qRT-PCR and transfecting cells with synthetic microRNA. Here, we report that miR-214 was significantly down-regulated in the cell lines used and in clinical samples of canine hemangiosarcoma. Restoration of miR-214 expression reduced cell growth and induced apoptosis in canine hemangiosarcoma cell lines through transcriptional activation of p53-regulated genes although miR-214 had a slight effect of growth inhibition on normal endothelial cells. We identified COP1, which is a critical negative regulator of p53, as a novel direct target of miR-214. COP1 was overexpressed and the specific COP1 knockdown induced apoptosis through transcriptional activation of p53-regulated genes as well as did miR-214-transfection in HSA cell lines. Furthermore, p53 knockdown abolished the miR-214-COP1-mediated apoptosis; thus, miR-214 and COP1 regulated apoptosis through controlling p53 in HSA. In conclusion, miR-214 functioned as a tumor suppressor in canine hemangiosarcoma by inducing apoptosis through recovering the function of p53. miR-214 down-regulation and COP1 overexpression is likely to contribute to tumorigenesis of HSA. Therefore, targeting miR-214-COP1-p53 axis would possibly be a novel effective strategy for treatment of canine hemangiosarcoma and capable of being applied to the development of novel therapeutics for human angiosarcoma.

Perturbation of energy metabolism by fatty-acid derivative AIC-47 and imatinib in BCR-ABL-harboring leukemic cells

In Ph-positive leukemia, imatinib brought marked clinical improvement; however, further improvement is needed to prevent relapse. Cancer cells efficiently use limited energy sources, and drugs targeting cellular metabolism improve the efficacy of therapy. In this study, we characterized the effects of novel anti-cancer fatty-acid derivative AIC-47 and imatinib, focusing on cancer-specific energy metabolism in chronic myeloid leukemia cells. AIC-47 and imatinib in combination exhibited a significant synergic cytotoxicity. Imatinib inhibited only the phosphorylation of BCR-ABL; whereas AIC-47 suppressed the expression of the protein itself. Both AIC-47 and imatinib modulated the expression of pyruvate kinase M (PKM) isoforms from PKM2 to PKM1 through the down-regulation of polypyrimidine tract-binding protein 1 (PTBP1). PTBP1 functions as alternative splicing repressor of PKM1, resulting in expression of PKM2, which is an inactive form of pyruvate kinase for the last step of glycolysis. Although inactivation of BCR-ABL by imatinib strongly suppressed glycolysis, compensatory fatty-acid oxidation (FAO) activation supported glucose-independent cell survival by up-regulating CPT1C, the rate-limiting FAO enzyme. In contrast, AIC-47 inhibited the expression of CPT1C and directly fatty-acid metabolism. These findings were also observed in the CD34(+) fraction of Ph-positive acute lymphoblastic leukemia cells. These results suggest that AIC-47 in combination with imatinib strengthened the attack on cancer energy metabolism, in terms of both glycolysis and compensatory activation of FAO.

A Novel Combination RNAi toward Warburg Effect by Replacement with miR-145 and Silencing of PTBP1 Induces Apoptotic Cell Death in Bladder Cancer Cells

Bladder cancer is one of the most difficult malignancies to control. We explored the use of a novel RNA-interference method for a driver oncogene regulating cancer specific energy metabolism by the combination treatment with a small interfering RNA (siRNA) and a microRNA. After transfection of T24 and 253JB-V cells with miR-145 and/or siR-PTBP1, we examined the effects of cell growth and gene expression by performing the trypan blue dye exclusion test, Western blot, Hoechst 33342 staining, reverse transcription polymerase chain reaction (RT-PCR), and electron microscopy. The anti-cancer effects of xenograft model mice with miR-145 and/or siR-PTBP1 were then assessed. The combination treatment induced the deeper and longer growth inhibition and reduced the levels of both mRNA and protein expression of c-Myc and polypyrimidine tract-binding protein 1 (PTBP1) more than each single treatment. Notably, the combination treatment not only impaired the cancer specific energy metabolism by inhibiting c-Myc/PTBP1/PKMs axis but also inactivated MAPK/ERK and PI3K/AKT pathways examined in vitro and in vivo. Furthermore, the combination treatment induced apoptosis or autophagy; but, in some cells, apoptotic cell death was accompanied by autophagy, because the condensation of chromatin and many autophagosomes were coexistent. This combination treatment could be a novel RNA-interference strategy through the systemic silencing of the Warburg effect-promoting driver oncogene PTBP1 in bladder cancer cells.

PKM1 is involved in resistance to anti-cancer drugs.

Resistance to chemotherapy is a crucial problem in the clinical situation. To overcome this issue, many mechanisms of chemoresistance have been elucidated so far. However, this problem still has not been solved completely. In this study, we investigated the mechanism of chemoresistance from the view of cancer metabolism-related genes, especially focusing on the expression profile of pyruvate kinase muscle (PKM) isoforms, which are rate-limiting enzymes in cancer-specific metabolism (Warburg effect). Herein, we showed that PKM1, which promotes oxidative phosphorylation (OXPHOS), was commonly up-regulated in various chemoresistant cells. To clarify the functions of PKM1 in chemoresistance, we investigated effects of PKM1 expression in DLD-1 parental, 5-FU-resistant and oxaliplatin-resistant DLD-1 cells. The overexpression of PKM1 resulted in resistance of the parental cells to 5-FU and oxaliplatin. Moreover, gene-silencing of PKM1 induced apoptosis in these cells including the resistant cells by causing a decrease in the mitochondrial membrane potential. Furthermore, combination therapy using 5-FU or oxaliplatin with siR-PKM1 was also effective against the resistant cells. Our findings should lead to the development of new agents that can cancel the chemoresistance from the view of cancer energy metabolism.