Highlights d N 6 -methyldeoxyadenosine (6mA) is enriched in human mitochondria DNA (mtDNA) d METTL4 can mediate mammalian mtDNA 6mA methylation d mtDNA 6mA affects mitochondrial transcription, replication, and activity d The 6mA level in mtDNA is significantly elevated under hypoxic stress

Gastric carcinoma is one of the most common cancers and lethal malignancies worldwide. Thus far, the regulatory mechanisms of its aggressiveness are still poorly understood.

Gastric carcinoma is one of the most common malignancies and a lethal cancer in the world. Notch signaling and transcription factors STAT3 (signal transducer and activator of transcription 3) and Twist regulate tumor development and are critical regulators of gastric cancer progression. Herein, the relationship among Notch, STAT3 and Twist pathways in the control of gastric cancer progression was studied. We found that Twist and phosphorylated STAT3 levels were promoted by the activated Notch1 receptor in human stomach adenocarcinoma SC-M1, embryonic kidney HEK293 and erythroleukemia K562 cells. Notch1 signaling dramatically induced Twist promoter activity through a C promoter binding factor-1-independent manner and STAT3 phosphorylation. Overexpression of Notch1 receptor intracellular domain (N1IC) enhanced the interaction between nuclear STAT3 and Twist promoter in cells. Gastric cancer progression of SC-M1 cells was promoted by N1IC through STAT3 phosphorylation and Twist expression including colony formation, migration and invasion. STAT3 regulated gastric cancer progression of SC-M1 cells via Twist. N1IC also elevated the progression of other gastric cancer cells such as AGS and KATO III cells through STAT3 and Twist. The N1IC-promoted tumor growth and lung metastasis of SC-M1 cells in mice were suppressed by the STAT3 inhibitor JSI-124 and Twist knockdown. Furthermore, Notch1 and Notch ligand Jagged1 expressions were significantly associated with phosphorylated STAT3 and Twist levels in gastric cancer tissues of patients. Taken together, these results suggest that Notch1/STAT3/Twist signaling axis is involved in progression of human gastric cancer and modulation of this cascade has potential for the targeted combination therapy.

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Transcription factor Ying Yang 1 (YY1) indirectly regulates the C promoter-binding factor 1 (CBF1)-dependent Notch1 signaling via direct interaction with the Notch1 receptor intracellular domain (N1IC) on CBF1-response elements. To evaluate the possibility that the N1IC might modulate the gene expression of YY1 target genes through associating with YY1 on the YY1-response elements, we herein investigated the effect of Notch1 signaling on the expression of YY1 target genes. We found that the N1IC bound to the double-stranded oligonucleotides of YY1-response element to activate luciferase activity of the reporter gene with YY1-response elements through a CBF1-independent manner. Furthermore, the N1IC also bound to the promoter of human c-myc oncogene, a YY1 target gene, to elevate c-myc expression via a CBF1-independent pathway. The activation of reporter genes with YY1-response elements or human c-myc promoter by N1IC depended on the formation of N1IC-YY1-associated complex. To delineate the role of the Notch signal pathway in tumorigenesis, K562 cell lines expressing the N1IC were established. Compared with control cells, the proliferation and the tumor growth of N1IC-expressing K562 cells were suppressed. Taken together, these results suggest that the N1IC enhances the human c-myc promoter activity that is partially modulated by YY1 through a CBF1-independent pathway. However, the enhancement of c-myc expression by N1IC is insufficient to promote the tumor growth of K562 cells.

INTRODUCTIONGastric cancer is one of the most frequent neoplasms and leading causes of cancer-related mortality worldwide (Terry et al., 2002;Executive Yuan, 2006). At present, curative surgery of its primary tumor and control of lymph node metastasis are still the mainstay of treatment for gastric cancer without distant metastasis . However, gastric cancer with distant metastasis remains incurable now. More than 95% of malignancies of the stomach are adenocarcinomas (Smith et al., 2006). The risk factors of human gastric cancer include diet, Helicobacter pylori infection, and accumulation of specific genetic alterations (Gonzalez et al., 2002;Ushijima and Sasako, 2004;Zheng et al., 2004). To date, the regulatory mechanism of aggressiveness in gastric cancer has not yet been clearly characterized. Therefore, it is essential to gain further insights into the physiology of gastric cancer and its accumulated genetic alterations.The inducible cyclooxygenase, COX-2, catalyzes the ratelimiting step in conversion of arachidonate into prostaglandin E 2 (PGE 2 ). It was shown that COX-2 expression is upregulated in gastric cancer (Ristimäki et al., 1997;Uefuji et al., 1998;Yamamoto et al., 1999;Lim et al., 2000). COX-2 expression is also correlated with depth of invasion, lymphatic vessel invasion, lymph node metastasis, and poor prognosis of human gastric carcinoma (Murata et al., 1999;Ohno et al., 2001;Shi et al., 2003;Chen et al., 2006). Epithelial-mesenchymal transition (EMT) plays a key role in development and tumorigenesis (for a review, see Thiery and Sleeman, 2006). In gastric cancer cells with fibroblastoid morphological changes, EMT signaling was suggested to promote motility and invasiveness through decreasing cell-cell adhesion (Katoh, 2005). Recently, COX-2 expression was found to enhance EMT stimulated by TGF-␤ through a PGE 2 -dependent manner in breast cancer (Neil et al., 2008). In this scenario, the induction of COX-2 expression in gastric cancer could further induce EMT to promote metastasis.The c-Myc promoter binding protein 1 (MBP-1), a negative regulator of c-myc expression, is ubiquitously expressed in normal human tissues (Ray et al., 1994 groove of the major c-Myc promoter, the P2 promoter (Chaudhary and Miller, 1995). The 37-kDa MBP-1 is produced by alternative translation initiation from ␣-enolase gene but without enzyme activity of enolase (Feo et al., 2000;Subramanian and Miller, 2000). So far, several MBP-1-associating proteins were identified, including histone deacetylase HDAC1 (Ghosh et al., 1999), MIP2A/sedlin (Ghosh et al., 2001), MEK5␣ (Ghosh et al., 2005a), NS1-BP (Perconti et al., 2007), and Notch1 receptor intracellular domain (Hsu et al., 2008). The downstream target genes of MBP-1 remain unclear exclusive of c-myc. It was reported that MBP-1 could regulate target genes at least through p53-p21 pathway (Ghosh et al., 2008). Mounting evidence indicates that both MBP-1 and ␣-enolase are involved in tumorigenesis of breast carcinoma (Ray et al., 1995), nonsmall cell lung cancer (Chan...

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Gastric carcinoma is one of the most common malignancies and the second most lethal cancer worldwide. The mechanisms underlying aggressiveness of gastric cancer still remain obscure. c-Myc promoter binding protein 1 (MBP-1) is a negative regulator of c-myc expression and ubiquitously expressed in normal human tissues. It is produced by alternative translation initiation of α-enolase gene. Both MBP-1 and α-enolase are involved in the control of tumorigenesis including gastric cancer. MicroRNAs (miRNAs) are involved in tumorigenesis and could have diagnostic, prognostic and therapeutic potential. In this study, whether miRNAs modulate tumorigenesis of gastric cancer cells through targeting MBP-1 was evaluated. We found that miR-363 targets 3'-untranslated region of human MBP-1/α-enolase messenger RNA. The exogenous miR-363 promotes growth, viability, progression, epithelial-mesenchymal transition and tumorsphere formation of SC-M1 gastric cancer cells through downregulation of MBP-1, whereas the knockdown of endogenous miR-363 suppresses tumorigenesis and progression of SC-M1 cells via upregulation of MBP-1. The miR-363/MBP-1 axis is also involved in the control of carcinogenesis in KATO III and SNU-16 gastric cancer cells. Furthermore, miR-363 induces the xenografted tumor growth and lung metastasis of SC-M1 cells through MBP-1 in vivo. Taken together, these results suggest that miR-363 plays an important role in the increment of gastric carcinogenesis via targeting MBP-1.