Regulation of DNA Polymerase by the LMP1 Oncoprotein of EBV through the Nuclear Factor-B Pathway

¹Institut National de la Sante et de la Recherche Medicale-U563, CPTP; ²Université Toulouse III Paul-Sabatier, Institut Claude de Préval, IFR30; and ³Centre National de la Recherche Scientifique-UMR-5089, IPBS, groupe Instabilité Génétique et Cancer, Toulouse, France; ⁴Centre National de la Recherche Scientifique-UMR-6101, CHU Dupuytren, Université de Limoges, Equipe labellisée La Ligue, Limoges, France; and ⁵Centre National de la Recherche Scientifique-UMR-8527, IBL, BP-447, Lille, France

^* To whom correspondence should be addressed. E-mail: fabienne.meggetto{at}inserm.fr.

	Abstract

The repair DNA polymerase (Pol), when overexpressed, plays a critical role in generating genetic instability via its interference with the genomic replication program. Up-regulation of Pol has been reported in many tumor types that exhibit genetic aberrations, including EBV-related B-cell lymphomas. However, the mechanisms responsible for its overexpression have never been examined. Here, we report that both expression and activity of Pol, in EBV-immortalized B cells, are induced by several natural genetic variants of LMP1, an oncoprotein associated with the vast majority of EBV-related tumors. Conversely, we found that the expression of Pol decreased when LMP1 signaling was down-regulated by a dominant negative of LMP1 or an inhibitor of the nuclear factor-B (NF-B) pathway, the main transduction pathway activated by LMP1, strongly supporting a role of NF-B in the LMP1-mediated Pol regulation. Using electrophoretic mobility shift assay experiments from several EBV-immortalized B-cell nuclear extracts, we identified an LMP1-dependent p50/c-Rel heterodimer on a proximal B binding site (-211 to -199nt) of the Pol promoter. This result was correlated with a specific Pol B transcriptional activity. Taken together, our data enlighten a new mechanism responsible for Pol overexpression in EBV-infected cells, mediated by LMP1 and dependent on NF-B activation. [Cancer Res 2009;69(12):5177–85]

Key Words: EBV, LMP1, Pol, NF-B, lymphoma