Cytoplasmic PARP‐1 promotes pancreatic cancer tumorigenesis and resistance

Abstract

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.

Regulation of pancreatic cancer TRAIL resistance by protein O-GlcNAcylation

“…Numerous human cancer cells, including pancreatic cancer cells, are resistant to TRAILinduced apoptosis and the molecular mechanisms underlying the resistance remain unclear, which makes it become a major huddle for the use of TRAIL-activating agents for cancer therapy despite its highly promising efficacy in targeting cancer cells. Our ongoing efforts in the search of strategies to sensitize TRAIL-induced apoptosis in resistant pancreatic cancer cells have uncovered that targeting the death inducing signaling complex (DISC) by either inducing expression of DR5 or converting survival signals to apoptotic singling is effective in promoting apoptosis of the TRAIL-resistant cancer cells 10,11,33,34 . The present studies offer novel molecular insights into sensitizing TRA-8-induced apoptosis of resistant pancreatic cancer cells at the essential initial step of the DISC formation, oligomerization of the death receptor, via inhibiting O-GlcNAcylation of DR5 ( Figure 6).…”

“…The animal study protocol was approved by the Institutional Animal Care and Use Committee (IACUC) at the University of Alabama at Birmingham. Eight-week old male athymic mice (Jackson Laboratory) were used for tumor inoculation as we described 11,33,34 . Stable OGT knockdown (shOGT) or control cells (shScr) were inoculated subcutaneously into the flanks of mice (1.0 ×10 6 cells/site, 5 mice/each group).…”

“…At the end of the experiment, tumors were removed from mice, half of each tumor was homogenized for Western blot analysis and the other half was fixed in 4% paraformaldehyde and embedded in paraffin for histology analysis by hematoxylin and eosin stain (H&E). TUNEL staining 11,34 TUNEL staining was conducted on tumor sections (DeadEnd Fluorometric TUNEL System; Promega) to determine cell death, while DAPI staining was used to localize nuclei. Stained specimens were examined microscopically (Leica M165 FC).…”

PARP1 Enhances Influenza A Virus Propagation by Facilitating Degradation of Host Type I Interferon Receptor

“…PARP1 has also been shown to interact with mitofilin, a mitochondrial protein, and it localizes in mitochondria, where it plays a role in the maintenance of mitochondrial DNA integrity (21). Nuclear-cytoplasmic expression of PARP1 has also been shown to occur in breast cancer (33) and pancreatic cancer (34) in human patients. Additionally, PARP1 localization is cytoplasmic during HIV-1 Vpr expression in cells (35), which could indicate that proteins of other viruses also have the potential to change PARP1 localization.…”

Natural Product Mediated Regulation of Death Receptors and Intracellular Machinery: Fresh from the Pipeline about TRAIL-Mediated Signaling and Natural TRAIL Sensitizers

“…Detailed mechanistic insights revealed that cytoplasmic PARP-1 was recruited into the TRA-8-activated DISC and sustained Src-mediated pro-survival signals [11]. However, the knockdown of PARP-1 not only interfered with the activation of Src but also improved TRA-8-mediated apoptotic cell death in BxPc-3 and MiaPaCa-2 cells [11].…”