Pancreatic cancer is a malignant neoplasm with a high mortality rate. Therapeutic agents that activate TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis have shown promising efficacy, but many pancreatic cancers are resistant to TRAIL therapy. Epigenetic regulation plays important roles in tumor pathogenesis and resistance, and a recent study indicated that the long non-coding RNA HOX transcript antisense RNA (HOTAIR) is overexpressed in pancreatic cancer. However, the role of HOTAIR in pancreatic cancer resistance to anticancer agents is unknown. The present study determined the role of HOTAIR in pancreatic cancer TRAIL resistance and investigated the underlying molecular mechanisms. We observed that TRAIL-resistant pancreatic cancer cells had higher levels of HOTAIR expression, whereas TRAIL-sensitive pancreatic cancer cells had lower HOTAIR levels. Overexpressing HOTAIR in TRAIL-sensitive cells attenuated TRAIL-induced apoptosis, and shRNA-mediated HOTAIR knockdown in TRAIL-resistant PANC-1 cells sensitized them to TRAIL-induced apoptosis. These results support a causative effect of HOTAIR on TRAIL sensitivity. Mechanistically, we found that increased HOTAIR expression inhibited the expression of the TRAIL receptor death receptor 5 (DR5), whereas HOTAIR knockdown increased DR5 expression. We further demonstrated that HOTAIR regulates DR5 expression via the epigenetic regulator enhancer of zeste homolog 2 (EZH2) and that EZH2 controls histone H3 lysine 27 trimethylation on the DR5 gene. Taken together, these results demonstrate that high HOTAIR levels increase the resistance of pancreatic cancer cells to TRAIL-induced apoptosis via epigenetic regulation of DR5 expression. Our study therefore supports the notion that targeting HOTAIR function may represent a strategy to overcome TRAIL resistance in pancreatic cancer.

Calmodulin antagonists promote TRA-8 therapy of resistant pancreatic cancer Calmodulin antagonists promote TRA-8 therapy of resistant pancreatic cancer

Cellular senescence, which can be defined as a stress response preventing the propagation of cells that have accumulated potentially oncogenic alterations, is invariably associated with a permanent cell cycle arrest. Enhancer of zeste homolog 2 (EZH2) as a member of polycomb group proteins and its targets include cell cycle regulatory proteins, which govern cell cycle progression and cellular senescence. In this study, we report that EZH2 depletion promotes the senescent state in human gastric cancer cells SGC-7901. We found that EZH2 functionally suppressed the senescent state in human gastric cancer cells SGC-7901. EZH2 depletion inhibited cell proliferation, arrested cellular cycle, restored features of a cellular senescence phenotype, and promoted doxorubicin-induced senescence. To prove that EZH2 expression contributes substantially to the change of key cell cycle regulators, we showed that p21 and p16 were activated to a certain extent upon EZH2 depletion and activation of p21 was in a p53-independent manner. Taken together, our data suggest that EZH2 depletion promotes the progression of senescence by mediating the activation of tumor suppressor genes p21 and p16, and could serve as a potential epigenetic target for gastric cancer therapy.

The poly(ADP‐ribose) polymerases (PARP) play important roles in repairing damaged DNA during intrinsic cell death. We recently linked PARP‐1 to death receptor (DR)‐activated extrinsic apoptosis, the present studies sought to elucidate the function of cytoplasmic PARP‐1 in pancreatic cancer tumorigenesis and therapy. Using human normal and pancreatic cancer tissues, we analyzed the prevalence of cytoplasmic PARP‐1 expression. In normal human pancreatic tissues, PARP‐1 expression was present in the nucleus; however, cytoplasmic PARP‐1 expression was identified in pancreatic cancers. Therefore, cytoplasmic PARP‐1 mutants were generated by site‐direct mutagenesis, to determine a causative effect of cytoplasmic PARP‐1 on pancreatic cancer tumorigenesis and sensitivity to therapy with TRA‐8, a humanized DR5 antibody. PARP‐1 cytoplasmic mutants rendered TRA‐8 sensitive pancreatic cancer cells, BxPc‐3 and MiaPaCa‐2, more resistant to TRA‐8‐induced apoptosis; whereas wild‐type PARP‐1, localizing mainly in the nucleus, had no effects. Additionally, cytoplasmic PARP‐1, but not wild‐type PARP‐1, increased resistance of BxPc‐3 cells to TRA‐8 therapy in a mouse xenograft model in vivo. Inhibition of PARP enzymatic activity attenuated cytoplasmic PARP‐1‐mediated TRA‐8 resistance. Furthermore, increased cytoplasmic PARP‐1, but not wild‐type PARP‐1, was recruited into the TRA‐8‐activated death‐inducing signaling complex and associated with increased and sustained activation of Src‐mediated survival signals. In contrast, PARP‐1 knockdown inhibited Src activation. Taken together, we have identified a novel function and mechanism underlying cytoplasmic PARP‐1, distinct from nuclear PARP‐1, in regulating DR5‐activated apoptosis. Our studies support an innovative application of available PARP inhibitors or new cytoplasmic PARP‐1 antagonists to enhance TRAIL therapy for TRAIL‐resistant pancreatic cancers.

Gemcitabine (GEM) resistance remains a challenging clinical issue to overcome in chemotherapy against pancreatic cancer. We previously demonstrated that miR-210 derived from pancreatic cancer stem cells enhanced the GEM-resistant properties of pancreatic cancer cells, thus identifying miR-210 as an oncogenic miRNA. Herein, we report the existence of an upstream effector that acts as a competing endogenous RNA (ceRNA) to miR-210. Bioinformatic screening was performed to identify lncRNAs with a binding relationship to miR-210. Overexpression and interference vectors were constructed to demonstrate the effect of ceRNA activity in pancreatic cell behavior, both in vitro and in vivo. DLEU2L (deleted in lymphocytic leukemia 2-like), which is expressed at low levels in pancreatic cancer tissues, was shown to exhibit a binding relationship with miR-210-3p. Overexpression of DLEU2L and silencing of miR-210-3p suppressed the proliferation, migration, and invasion of pancreatic cancer cells while promoting apoptosis. These effects occurred via the inhibition of the Warburg effect (aerobic glycolysis) and AKT/mTOR signaling. In addition, we showed that BRCA2 is a target gene of miR-210-3p, and the downregulation of miR-210-3p by DLEU2L effectively induced an upregulation of BRCA2 via the ceRNA mechanism. In vivo, DLEU2L overexpression and miR-210-3p interference suppressed pancreatic tumor progression, consistent with the results of in vitro studies. The findings of our study establish DLEU2L as a ceRNA to miR-210-3p and reveal the critical role of the DLEU2L/miR-210-3p crosstalk in targeting GEM resistance.