Jun Koseki

MicroRNA-1246 expression associated with CCNG2-mediated chemoresistance and stemness in pancreatic cancer

Background:Pancreatic cancer has a poor prognosis because of its high refractoriness to chemotherapy and tumour recurrence, and these properties have been attributed to cancer stem cells (CSCs). MicroRNA (miRNA) regulates various molecular mechanisms of cancer progression associated with CSCs. This study aimed to identify the candidate miRNA and to characterise the clinical significance.Methods:We established gemcitabine-resistant Panc1 cells, and induced CSC-like properties through sphere formation. Candidate miRNAs were selected through microarray analysis. The overexpression and knockdown experiments were performed by evaluating the in vitro cell growth and in vivo tumourigenicity. The expression was studied in 24 pancreatic cancer samples after laser captured microdissection and by immunohistochemical staining.Results:The in vitro drug sensitivity of pancreatic cancer cells was altered according to the miR-1246 expression via CCNG2. In vivo, we found that miR-1246 could increase tumour-initiating potential and induced drug resistance. A high expression level of miR-1246 was correlated with a worse prognosis and CCNG2 expression was significantly lower in those patients.Conclusions:miR-1246 expression was associated with chemoresistance and CSC-like properties via CCNG2, and could predict worse prognosis in pancreatic cancer patients.

α-1-C-butyl-1,4-dideoxy-1,4-imino-l-arabinitol as a second-generation iminosugar-based oral α-glucosidase inhibitor for improving postprandial hyperglycemia.

We report on the synthesis and the biological evaluation of a series of α-1-C-alkylated 1,4-dideoxy-1,4-imino-l-arabinitol (LAB) derivatives. The asymmetric synthesis of the derivatives was achieved by asymmetric allylic alkylation, ring-closing metathesis, and Negishi cross-coupling as key reactions. α-1-C-Butyl-LAB is a potent inhibitor of intestinal maltase, isomaltase, and sucrase, with IC50 values of 0.13, 4.7, and 0.032 μM, respectively. Matrix-assisted laser desorption ionization time-of-flight mass spectrometric analysis revealed that this compound differs from miglitol in that it does not influence oligosaccharide processing and the maturation of glycoproteins. A molecular docking study of maltase-glucoamylase suggested that the interaction modes and the orientations of α-1-C-butyl-LAB and miglitol are clearly different. Furthermore, α-1-C-butyl-LAB strongly suppressed postprandial hyperglycemia at an early phase, similar to miglitol in vivo. It is noteworthy that the effective dose was about 10-fold lower than that for miglitol. α-1-C-Butyl-LAB therefore represents a new class of promising compounds that can improve postprandial hyperglycemia.

Role of pyruvate kinase M2 in transcriptional regulation leading to epithelial–mesenchymal transition

Significance Our study shows that pyruvate kinase M2 (PKM2), an alternatively spliced variant of the pyruvate kinase gene, mediates epithelial–mesenchymal transition (EMT), which is critical for cancer cells to acquire invasive potential. Our study demonstrates that EMT stimulates nuclear translocation of PKM2 and decreases epithelial cadherin transcription (a requirement for EMT induction). Our results also demonstrate that PKM2 interacts with the transcriptional factor TGF-β–induced factor homeobox 2, which induces the deacetylation of histone H3, resulting in repressed E-cadherin expression. The precise understanding of nuclear PKM2 function suggests the potential for a model preventing cancer metastasis. Pyruvate kinase M2 (PKM2) is an alternatively spliced variant of the pyruvate kinase gene that is preferentially expressed during embryonic development and in cancer cells. PKM2 alters the final rate-limiting step of glycolysis, resulting in the cancer-specific Warburg effect (also referred to as aerobic glycolysis). Although previous reports suggest that PKM2 functions in nonmetabolic transcriptional regulation, its significance in cancer biology remains elusive. Here we report that stimulation of epithelial–mesenchymal transition (EMT) results in the nuclear translocation of PKM2 in colon cancer cells, which is pivotal in promoting EMT. Immunoprecipitation and LC-electrospray ionized TOF MS analyses revealed that EMT stimulation causes direct interaction of PKM2 in the nucleus with TGF-β–induced factor homeobox 2 (TGIF2), a transcriptional cofactor repressor of TGF-β signaling. The binding of PKM2 with TGIF2 recruits histone deacetylase 3 to the E-cadherin promoter sequence, with subsequent deacetylation of histone H3 and suppression of E-cadherin transcription. This previously unidentified finding of the molecular interaction of PKM2 in the nucleus sheds light on the significance of PKM2 expression in cancer cells.

Tumour-suppressive function of SIRT4 in human colorectal cancer.

Background:SIRT4, which is localised in the mitochondria, is one of the least characterised members of the sirtuin family of nicotinamide adenine dinucleotide-dependent enzymes that play key roles in multiple cellular processes such as metabolism, stress response and longevity. There are only a few studies that have characterised its function and assessed its clinical significance in human cancers.Methods:We established colorectal cancer cell lines (SW480, HCT116, and HT29) overexpressing SIRT4 and investigated their effects on proliferation, migration and invasion, as well as E-cadherin expression, that negatively regulates tumour invasion and metastases. The associations between SIRT4 expression in colorectal cancer specimens and clinicopathological features including prognosis were assessed by immunohistochemistry.Results:SIRT4 upregulated E-cadherin expression and suppressed proliferation, migration and invasion through inhibition of glutamine metabolism in colorectal cancer cells. Moreover, SIRT4 expression in colorectal cancer decreased with the progression of invasion and metastasis, and a low expression level of SIRT4 was correlated with a worse prognosis.Conclusions:SIRT4 has a tumour-suppressive function and may serve as a novel therapeutic target in colorectal cancer.

Design and Synthesis of Labystegines, Hybrid Iminosugars from LAB and Calystegine, as Inhibitors of Intestinal α-Glucosidases: Binding Conformation and Interaction for ntSI

This paper identifies the required configuration and orientation of α-glucosidase inhibitors, miglitol, α-1-C-butyl-DNJ, and α-1-C-butyl-LAB for binding to ntSI (isomaltase). Molecular dynamics (MD) calculations suggested that the flexibility around the keyhole of ntSI is lower than that of ctSI (sucrase). Furthermore, a molecular-docking study revealed that a specific binding orientation with a CH-π interaction (Trp370 and Phe648) is a requirement for achieving a strong affinity with ntSI. On the basis of these results, a new class of nortropane-type iminosugars, labystegines, hybrid iminosugars of LAB and calystegine, have been designed and synthesized efficiently from sugar-derived cyclic nitrones with intramolecular 1,3-dipolar cycloaddition or samarium iodide catalyzed reductive coupling reaction as the key step. Biological evaluation showed that our newly designed 3(S)-hydroxy labystegine (6a) inherited the selectivity against intestinal α-glucosidases from LAB, and its inhibition potency was 10 times better than that of miglitol. Labystegine, therefore, represents a promising new class of nortropane-type iminosugar for improving postprandial hyperglycemia.

Oncometabolite D-2-Hydroxyglurate Directly Induces Epithelial-Mesenchymal Transition and is Associated with Distant Metastasis in Colorectal Cancer

Deranged metabolism is a hallmark of cancer, playing a significant role in driving the disease process. One such example is the induction of carcinogenesis by the oncometabolite D-2 hydroxyglutarate (D-2HG), which is produced by the mutated enzyme isocitrate dehydrogenase (IDH) occurring in subsets of leukaemias and brain tumours. The oncogenic property of D-2HG appears to stem from its ability to interfere with the activities of α-ketoglutarate-dependent dioxygenases, including the Jumonji family histone demethylases. Here, we find in colorectal cancer cells that even in the absence of IDH mutation, the levels of D-2HG and its enantiomer L-2HG were elevated through glutamine anaplerosis. D-2HG, but not L-2HG, increased the trimethylation of histone H3 lysine 4 of the promoter region of ZEB1, a master regulator of epithelial-mesenchymal transition (EMT), and increased the expression of the ZEB1 gene to directly induce EMT in colorectal cancer cells. EMT promotes the ability of cancer cells to invade the local tissue and enter into the bloodstream, leading to distant organ metastasis. D-2HG levels were elevated in colorectal cancer specimens, particularly in those associated with distant metastasis, supporting the observations in vitro and implicating the contribution of D-2HG in metastasis, the major cause of death in this disease.

MicroRNAs Induce Epigenetic Reprogramming and Suppress Malignant Phenotypes of Human Colon Cancer Cells

Although cancer is a genetic disease, epigenetic alterations are involved in its initiation and progression. Previous studies have shown that reprogramming of colon cancer cells using Oct3/4, Sox2, Klf4, and cMyc reduces cancer malignancy. Therefore, cancer reprogramming may be a useful treatment for chemo- or radiotherapy-resistant cancer cells. It was also reported that the introduction of endogenous small-sized, non-coding ribonucleotides such as microRNA (miR) 302s and miR-369-3p or -5p resulted in the induction of cellular reprogramming. miRs are smaller than the genes of transcription factors, making them possibly suitable for use in clinical strategies. Therefore, we reprogrammed colon cancer cells using miR-302s and miR-369-3p or -5p. This resulted in inhibition of cell proliferation and invasion and the stimulation of the mesenchymal-to-epithelial transition phenotype in colon cancer cells. Importantly, the introduction of the ribonucleotides resulted in epigenetic reprogramming of DNA demethylation and histone modification events. Furthermore, in vivo administration of the ribonucleotides in mice elicited the induction of cancer cell apoptosis, which involves the mitochondrial Bcl2 protein family. The present study shows that the introduction of miR-302s and miR-369s could induce cellular reprogramming and modulate malignant phenotypes of human colorectal cancer, suggesting that the appropriate delivery of functional small-sized ribonucleotides may open a new avenue for therapy against human malignant tumors.

Combined evaluation of hexokinase 2 and phosphorylated pyruvate dehydrogenase-E1α in invasive front lesions of colorectal tumors predicts cancer metabolism and patient prognosis.

Although numerous studies have shown the significance of cancer‐specific aerobic glycolysis, how glycolysis contributes to tumor invasion, a critical phenomenon in metastasis, remains unclear. With regard to colorectal cancer (CRC), we studied two critical gate enzymes, hexokinase 2 (HK2), which is involved in glycolysis, and phosphorylated pyruvate dehydrogenase‐E1α (p‐PDH), which is involved in oxidative phosphorylation (OxPhos). Immunohistochemical analyses using anti‐HK2 and p‐PDH antibodies were performed on surgically resected CRC samples (n = 104), and the expression in invasive front lesions of tumors was assessed. Positive HK2 expression correlated with extensive tumor diameter (P = 0.0460), advanced tumor depth (P = 0.0395), and presence of lymph node metastasis (P = 0.0409). Expression of p‐PDH tended to be higher in right‐sided CRCs than in left‐sided CRCs (P = 0.0883). In survival analysis, the combined evaluation of positive HK2 and negative p‐PDH was associated with reduced recurrence‐free survival (RFS) (P = 0.0169 in all stages and P = 0.0238 in Stage II and III patients, respectively). This evaluation could predict RFS more precisely than the independent evaluation. The present study indicated that high HK2 expression combined with low p‐PDH expression in the invasive front lesions of CRC tumors is predictive of tumor aggressiveness and survival of CRC cases.

Metabolic Adaptation to Nutritional Stress in Human Colorectal Cancer

Tumor cells respond to their microenvironment, which can include hypoxia and malnutrition, and adapt their metabolism to survive and grow. Some oncogenes are associated with cancer metabolism via regulation of the related enzymes or transporters. However, the importance of metabolism and precise metabolic effects of oncogenes in colorectal cancer remain unclear. We found that colorectal cancer cells survived under the condition of glucose depletion, and their resistance to such conditions depended on genomic alterations rather than on KRAS mutation alone. Metabolomic analysis demonstrated that those cells maintained tricarboxylic acid cycle activity and ATP production under such conditions. Furthermore, we identified pivotal roles of GLUD1 and SLC25A13 in nutritional stress. GLUD1 and SLC25A13 were associated with tumor aggressiveness and poorer prognosis of colorectal cancer. In conclusion, GLUD1 and SLC25A13 may serve as new targets in treating refractory colorectal cancer which survive in malnutritional microenvironments.

BRAF V600E inhibition stimulates AMP-activated protein kinase-mediated autophagy in colorectal cancer cells.

Although BRAFV600E mutation is associated with adverse clinical outcomes in patients with colorectal cancer (CRC), response and resistance mechanisms for therapeutic BRAFV600E inhibitors remains poorly understood. In the present study, we demonstrate that selective BRAFV600E inhibition activates AMP-activated protein kinase (AMPK), which induces autophagy as a mechanism of therapeutic resistance in human cancers. The present data show AMPK-dependent cytoprotective roles of autophagy under conditions of therapeutic BRAFV600E inhibition, and AMPK was negatively correlated with BRAFV600E-dependent activation of MEK-ERK-RSK signaling and positively correlated with unc-51-like kinase 1 (ULK1), a key initiator of autophagy. Furthermore, selective BRAFV600E inhibition and concomitant suppression of autophagy led to the induction of apoptosis. Taken together, present experiments indicate that AMPK plays a role in the survival of BRAFV600E CRC cells by selective inhibition and suggest that the control of autophagy contributes to overcome the chemoresistance of BRAFV600E CRC cells.