Pancreatic adenocarcinoma up-regulated factor (PAUF) enhances the expression of beta-catenin, leading to a rapid proliferation of pancreatic cells

It is not yet understood how the enhanced expression of pancreatic adenocarcinoma up-regulated factor (PAUF; a novel oncogene identified in our recent studies), contributes to the oncogenesis of pancreatic cells. We herein report that PAUF up-regulates the expression and transcriptional activity of beta-catenin while the suppression of PAUF by shRNA down-regulates beta-catenin. The induction of beta-catenin by PAUF is mediated by the activities of Akt and GSK-3beta, but inhibition of downstream ERK does not reduce beta-catenin expression. To test whether PAUF emulates either the Wnt3a-mediated or the protein kinase A-mediated signaling pathway for the stabilization of beta-catenin, we examined the phosphorylation status of beta-catenin in the presence of PAUF compared with that of beta-catenin during treatment with Wnt3a or dibutyryl cAMP, a cell permeable cyclic AMP analogue. PAUF expression induces phosphorylation at Ser-33/37/Thr-41 and Ser-675 of beta-catenin but no phosphorylation at Ser-45, indicating that a unique phosphorylation pattern of beta-catenin is caused by PAUF. Finally, the expression of PAUF up-regulates both cyclin-D1 and c-Jun, target genes of beta-catenin, leading to a rapid proliferation of pancreatic cells; conversely decreased PAUF expression (by shRNA) results in the reduced proliferation of pancreatic cells. Treatment with hexachlorophene (an inhibitor of beta-catenin) reduces the proliferation of pancreatic cells despite the presence of PAUF. Taken together, we propose that PAUF can up-regulate and stabilize beta-catenin via a novel pattern of phosphorylation, thereby contributing to the rapid proliferation of pancreatic cancer cells.

STP-A11, an oncoprotein of Herpesvirus saimiri augments both NF-kappaB and AP-1 transcription activity through TRAF6

Herpesvirus saimiri (HVS), a member of the gamma-herpesvirus family, encodes an oncoprotein called Saimiri Transforming Protein (STP) which is required for lymphoma induction in non-human primates. However, a detailed mechanism of STP-A11-induced oncogenesis has not been revealed yet. We first report that STP-A11 oncoprotein interacts with TNF-alpha receptor-associated factor (TRAF) 6 in vivo and in vitro. Mutagenesis analysis of the TRAF6-binding motif 10PQENDE15 in STP-A11 reveals that Glu (E)12 residue is critical for binding to TRAF6 and NF-kappaB activation. Interestingly, co-expression of E12A mutant, lack of TRAF6 binding, with cellular Src (Src) results in decreased transcriptional activity of Stat3 and AP-1, a novel target of STP-A11 compared to that of wild type. Furthermore, the presence of STP-A11 enhances the association of TRAF6 with Src and induces the translocation of both TRAF6 and Src to a nonionic detergent-insoluble fraction. Taken together, these studies suggest that STP-A11 oncoprotein up-regulates both NF-kappaB and AP-1 transcription activity through TRAF6, which would ultimately contribute cellular transformation.