UEV1A Is a Candidate Proto-Oncogene That Participates in NF-B Activation
EE Torlakovic, L Pelzer, N Syed, K Lockheart, EC Marginean, B Davidson, W Xiao. College of Medicine, University of Saskatchewan, Saskatoon, SK, Canada; Rikshospitalet-Radiumhospitalet Medical Center, University of Oslo, Oslo, Norway
Background: Activation of NF-B signaling pathway is considered to be pro-survival and anti-apoptotic; hence, NF-B activation could provide a hallmark phenotype for cancer. Recent observations suggest that TRAF (E3) and Ubc13-Uev1A (E2)-mediated Lys63-linked polyubiquitination plays a central role in the NF-B signaling pathway. We hypothesize that Uev1A functions as a regulatory subunit of the Ubc13-Uev1A and TRAF-mediated NF-B pathway and that the abnormal expression of UEV1A plays a critical role in tumorigenesis. Also, a universal overexpression of UEV1A mRNA was previously described in all tumor cell lines examined.
Design: Stable HepG2 transfectants expressing UEV1A-myc at different levels were established and the suppression of UEV1 was achieved by RNAi. The UEV1 transcript level was evaluated by RT-PCR with UEV1A-specific primers in 7 fresh samples of colon adenocarcinomas. We have raised mAbs specific for the N-terminal domain of Uev1A and used it for immunohistochemical (IHC) detection of Uev1A protein expression in formalin-fixed, paraffin-embedded samples of 58 patients (20 gastric and 38 colorectal adenocarcinomas with matched samples of normal mucosa and matched metastatic tumors (191 samples in toto). NF-B activation was determined by IHC detecting nuclear translocation of its p65 subunit.
Results: 2.5-fold UEV1A expression resulted in an up to tenfold increase in NF-B activity and the activation of its target genes, as assayed by Bcl-2 western blot. RNAi suppression of Uev1 reverted the NF-B activity to below the basal level. RT-PCR showed elevated UEV1A mRNA in 1/4 primary colon cancers and 2/3 metastatic tumors. Uev1A protein expression was not detected by IHC in histologically normal mucosa, but it was expressed in 6/20 primary gastric and 21/46 primary and 44/56 metastatic colorectal tumors (p<0.0001, Chi-Square). There was almost perfect correlation between NF-B activation and Uev1A (p<0.0001). Uev1A was not detected in 50% of tumors showing NF-B activation, suggesting that in these tumors NF-B is activated through mechanisms other than Uev1A upregulation.
Conclusions: UEV1A is a candidate proto-oncogene that participates in NF-B activation and it may play a critical role in about 1/2 of gastric and colorectal tumors showing NF-B activation. It also appears to play a positive role in tumor progression since it is more often observed in metastatic than in primary tumors.
Monday, March 9, 2009 1:00 PM
Poster Session II # 84, Monday Afternoon