High expression of MDM2 protein and low rate of p21(WAF1/CIP1) expression in SCID mice Epstein Barr virus-induced lymphoproliferation

Epstein-Barr virus nuclear antigen 3C augments Mdm2-mediated p53 ubiquitination and degradation by deubiquitinating Mdm2

Epstein-Barr virus (EBV) nuclear antigen 3C (EBNA3C) is one of the essential latent antigens for primary B-cell transformation. Previous studies established that EBNA3C facilitates degradation of several vital cell cycle regulators, including the retinoblastoma (pRb) and p27(KIP) proteins, by recruitment of the SCF(Skp2) E3 ubiquitin ligase complex. EBNA3C was also shown to be ubiquitinated at its N-terminal residues. Furthermore, EBNA3C can bind to and be degraded in vitro by purified 20S proteasomes. Surprisingly, in lymphoblastoid cell lines, EBNA3C is extremely stable, and the mechanism for this stability is unknown. In this report we show that EBNA3C can function as a deubiquitination enzyme capable of deubiquitinating itself in vitro as well as in vivo. Functional mapping using deletion and point mutational analysis showed that both the N- and C-terminal domains of EBNA3C contribute to the deubiquitination activity. We also show that EBNA3C efficiently deubiquitinates Mdm2, an important cellular proto-oncogene, which is known to be overexpressed in several human cancers. The data presented here further demonstrate that the N-terminal domain of EBNA3C can bind to the acidic domain of Mdm2. Additionally, the N-terminal domain of EBNA3C strongly stabilizes Mdm2. Importantly, EBNA3C simultaneously binds to both Mdm2 and p53 and can form a stable ternary complex; however, in the presence of p53 the binding affinity of Mdm2 toward EBNA3C was significantly reduced, suggesting that p53 and Mdm2 might share a common overlapping domain of EBNA3C. We also showed that EBNA3C enhances the intrinsic ubiquitin ligase activity of Mdm2 toward p53, which in turn facilitated p53 ubiquitination and degradation. Thus, manipulation of the oncoprotein Mdm2 by EBNA3C potentially provides a favorable environment for transformation and proliferation of EBV-infected cells.

MDM2 Promoter SNP309 Is Associated with Risk of Occurrence and Advanced Lymph Node Metastasis of Nasopharyngeal Carcinoma in Chinese Population

PURPOSE

Mouse double minute 2 (MDM2) is a key negative regulator of the p53 activity. Recently, a polymorphism in the MDM2 intronic promoter, SNP309, was shown to influence MDM2 expression and p53 activity. We examined whether the SNP309 was related to the risk of developing nasopharyngeal carcinoma (NPC) among Chinese populations.

EXPERIMENTAL DESIGN

We genotyped the SNP309 in two independent case-control populations in southern China, one is from Guangxi province (including 593 NPC patients and 480 controls) and the other is from Guangdong province (including 239 patients and 286 controls), by PCR direct sequencing. Multivariate logistic regression analysis was used to calculate adjusted odds ratio (OR) and 95% confidence interval (95% CI).

RESULTS

We observed that compared with the TT genotype, the genotypes containing G allele (GT + GG genotype) were associated with significant increased susceptibility to NPC in both Guangxi (OR, 1.43; 95% CI, 1.04-1.91) and Guangdong population (OR, 1.53; 95% CI, 1.00-2.36). When these two sample sets were combined, the OR of the GT + GG genotype developing NPC was 1.45 (95% CI, 1.12-1.85) compared with the TT genotype. Furthermore, compared with the TT genotype, the GT + GG genotype was also significantly associated with the advanced lymph node metastasis (OR, 1.84; 95% CI, 1.09-3.05).

CONCLUSIONS

Our findings suggest that the MDM2 SNP309 may be a risk factor for the occurrence and advanced neck lymph node metastasis of NPC in Chinese population.

Isolated EBV lymphoproliferative disease in a child with Wiskott-Aldrich syndrome manifesting as cutaneous lymphomatoid granulomatosis and responsive to anti-CD20 immunotherapy

Patients with primary immunodeficiencies such as the Wiskott-Aldrich syndrome (WAS) are prone to develop Epstein-Barr virus (EBV) related lymphoproliferative disorders (LPDs). EBV LPD is most frequently seen in patients receiving immunosuppressive treatment after organ transplantation (post-transplant lymphoproliferative disorder), but can also arise in the primary immunodeficiencies. Typically, EBV LPD presents as a diffuse systemic disease with lymphadenopathy and organ involvement. A rare angiocentric and angiodestructive form of EBV associated B cell LPD, lymphomatoid granulomatosis (LyG), has also been reported in association with WAS. LyG most commonly involves the lung, but can also be seen in brain, kidney, liver, and skin. This report describes the case of a 16 year old boy with WAS who presented with an isolated non-healing ulcerating skin lesion. Biopsy revealed an EBV related LPD with the histological features of LyG. This cutaneous lesion responded dramatically to treatment with specific anti-CD20 immunotherapy and the patient remains clinically free of LPD at 18 months.