No abstract

Background: Pancreatic cancer is one of the most lethal types of cancer with extremely poor diagnosis and prognosis, and chemo-resistance remains a major challenge. The dynamic and reversible N 6-methyladenosine (m 6 A) RNA modification has emerged as a new layer of epigenetic gene regulation. Methods: qRT-PCR and IHC were applied to examine ALKBH5 levels in normal and pancreatic cancer tissues. Cancer cell proliferation and chemo-resistance were evaluated by clonogenic formation, chemosensitivity detection, and Western blotting assays. m 6 A-seq was performed to identify target genes. We evaluated the inhibitory effect of ALKBH5 in both in vivo and in vitro models. Results: Here, we show that m 6 A demethylase ALKBH5 is downregulated in gemcitabine-treated patient-derived xenograft (PDX) model and its overexpression sensitized pancreatic ductal adenocarcinoma (PDAC) cells to chemotherapy. Decreased ALKBH5 levels predicts poor clinical outcome in PDAC and multiple other cancers. Furthermore, silencing ALKBH5 remarkably increases PDAC cell proliferation, migration, and invasion both in vitro and in vivo, whereas its overexpression causes the opposite effects. Global m 6 A profile revealed altered expression of certain ALKBH5 target genes, including Wnt inhibitory factor 1 (WIF-1), which is correlated with WIF-1 transactivation and mediation of the Wnt pathway. Conclusions: Our work uncovers the tumor suppressive and chemo-sensitizing function for ALKBH5, which provides insight into critical roles of m 6 A methylation in PDAC.

A clinicopathological analysis of the risk factors for lymph node metastasis was performed in 177 patients with submucosal invasive colorectal carcinoma (CRC). The submucosal deepest invasive portion was histologically subclassified as well (W), moderately (M), or poorly (Por) differentiated. M type was further subdivided into moderately-well (Mw) and moderately-poorly (Mp) differentiated. The pattern of tumor growth was classified as polypoid growth (PG) and non-polypoid growth (NPG). Lymph node metastasis was detected in 21 (12%) of the 177 patients. Macroscopically, type IIc and IIa + IIc lesions showed a significantly higher incidence of lymph node metastasis (44% and 30%) than type IIa and I (4% and 8%). Regarding the histologic subclassification, Por and Mp lesions showed a significantly higher incidence of lymph node metastasis (67% and 37%) than W and Mw lesions (4% and 14%). NPG tumors showed a significantly higher incidence of lymph node metastasis (29%) than PG tumors (7%). The depth of submucosal invasion and lymphatic invasion (ly) were also significantly correlated with the incidence of lymph node metastasis (submucosal scanty (sm-s) invasion 4%, massive invasion 20%; ly(+) 23%, ly(-) 5%). None of the lesions with both sm-s invasion and of W or Mw type showed lymph node metastasis. These results indicate that submucosal invasive CRC with both sm-s invasion and of W or Mw type, which shows no ly, is the appropriate indication for endoscopic curative treatment.

Nonessential tRNA modifications by methyltransferases are evolutionarily conserved and have been reported to stabilize mature tRNA molecules and prevent rapid tRNA decay (RTD). The tRNA modifying enzymes, NSUN2 and METTL1, are mammalian orthologs of yeast Trm4 and Trm8, which are required for protecting tRNA against RTD. A simultaneous overexpression of NSUN2 and METTL1 is widely observed among human cancers suggesting that targeting of both proteins provides a novel powerful strategy for cancer chemotherapy. Here, we show that combined knockdown of NSUN2 and METTL1 in HeLa cells drastically potentiate sensitivity of cells to 5-fluorouracil (5-FU) whereas heat stress of cells revealed no effects. Since NSUN2 and METTL1 are phosphorylated by Aurora-B and Akt, respectively, and their tRNA modifying activities are suppressed by phosphorylation, overexpression of constitutively dephosphorylated forms of both methyltransferases is able to suppress 5-FU sensitivity. Thus, NSUN2 and METTL1 are implicated in 5-FU sensitivity in HeLa cells. Interfering with methylation of tRNAs might provide a promising rationale to improve 5-FU chemotherapy of cancer.

The expression of cyclin E in human colorectal adenomas and adenocarcinomas was examined immunohistochemically to elucidate the role of cyclin E in the colorectal carcinogenesis. The expression of cyclin E was detected in 25% (91/358) of the adenomas and 56% (149/267) of the adenocarcinomas. The incidence of strongly positive cases was significantly higher in the adenocarcinomas (20%) than in the adenomas (5%) (P < 0.01). Among adenomas, a significant correlation was noticed between the expression of cyclin E and the grade of atypia. The incidence of cyclin E expression was significantly higher in the adenocarcinomas without an adenoma component (62%; 104/169) than in those with this component (46%; 45/98) (P < 0.05). Furthermore, the incidence of the cyclin E expression was higher in stages 1 and 2 carcinoma than in stage 0 and stages 3 and 4 carcinoma. The expression of cyclin E was the most prominent in tumors invading the submucosa and muscularis propria. The expression of cyclin E was significantly correlated with the proliferative activity of the tumor cells measured by Ki-67 antigen expression (P < 0.01). It was also correlated with the expression of p53 protein in the tumor cells (P < 0.01). Overexpression of cyclin E and subsequent deregulation of cell cycle may contribute to the development and early progression of the colorectal carcinomas.