EBNA3C Can Modulate the Activities of the Transcription Factor Necdin in Association with Metastasis Suppressor Protein Nm23-H1

Abstract

Previous studies have demonstrated the interaction between the Epstein-Barr virus (EBV) nuclear antigen 3C (EBNA3C) and the metastatic suppressorEpstein-Barr virus (EBV) is a human gammaherpesvirus which predominantly targets B cells and epithelial cells and is associated with a number of human cancers, including Burkitt's lymphoma, nasopharyngeal carcinoma, Hodgkin's disease, AIDS-associated and transplant-associated immunoblastic lymphoma, and, controversially, invasive breast carcinoma (9, 61). In vitro infection of B cells with EBV gives rise to lymphoblastoid cell lines (LCLs) which express a subset of 12 latent viral transcripts (61). These 12 transcripts encode six nuclear antigens (EBNAs), three latent membrane proteins, two early RNAs (32), and the BARF transcripts (61). Studies have shown that EBNA3C, one of the six nuclear antigens, interacts with the suppressor of cell migration and metastasis Nm23-H1 (69). This interaction between Nm23-H1 and EBNA3C has been shown to result in an increase in transcriptional activity on a targeted responsive promoter (70). Nm23-H1 tethered to DNA by a Gal4 DNA binding domain can activate transcription from a basal promoter at relatively low levels. However, when EBNA3C was introduced, the transactivation activity was shown to be substantially increased (70). These results suggest that Nm23-H1 may possess transcriptional regulatory activities which could function independent of its direct binding with DNA. This could possibly be through its interaction with EBNA3C (69). Interestingly, the presence of EBNA3C mediates the cellular translocation of Nm23-H1 from a mostly cytoplasmic to a predominantly nuclear signal. Moreover, EBNA3C can reverse the antimigratory effects of Nm23-H1 in vitro (69) as well as in vivo (23). The interaction between EBNA3C and Nm23-H1 has also been shown to be important in the regulation of COX-2, MMP-9, and alpha V integrin (13,24,26).The Nm23 gene family is highly conserved among a wide variety of eukaryotic species. Eight Nm23 genes have been identified for humans: Nm23-H1 (62), Nm23-H2 (68), Nm23-H3 (79), Nm23-H4 (45), Nm23-H5 (47), 76),. Members of the Nm23 gene family are structurally and functionally conserved, consisting of four to six identically folded subunits enclosing a large (25-Å) central cavity (84). Expression of Nm23 genes has been linked to suppression of tumor metastasis, differentiation, apoptosis, proliferation, and DNA mutation rate (14) and is also associated with nucleoside diphosphate (NDP) kinase activity (7,49,82), serine phosphorylation (8,20,37,48), histidine protein kinase activities (81), and transcriptional stimulatory activities (2,6,59,60). The human Nm23-H1 gene product is the best-characterized member of this family of proteins. It is 152 amino acids (aa) in length with leucine repeats and alpha-helical and basic domains (61). Nm23-H1 is 88% identical to Nm23-H2 and maps 4 kb apart at position q21.3 on

Protein–protein interactions: a mechanism regulating the anti-metastatic properties of Nm23-H1

“…Subsequent work has confirmed this interaction in lymphoblastoid cells (Murakami et al 2005). The Robertson lab developed the hypothesis that the Nm23-H1/EBNA-3C interaction regulates the latter's transcriptional activity, including the targets Cox-2 and αV integrin; these effects may be indirect, mediated through interactions with the Sp1, Necdin, and GATA transcription factors (Kaul et al 2009;Choudhuri et al 2006). EBNA-3C has been demonstrated to induce tumor cell motility in vitro and metastasis in vivo, and increased Nm23-H1 expression counters this phenotype (Murakami et al 2005;Kaul et al 2007;Subramanian et al 2001a).…”

Impact of EBV Essential Nuclear Protein EBNA-3C on B-Cell Proliferation and Apoptosis

“…Later, in our laboratory, an amino acid sequence Blast analysis of the EBNA-3C-interacting domain demonstrated a significant sequence homology to Necdin, a member of the MAGE family of proteins known to regulate multiple cellular processes, including cell cycle regulation and apoptosis [64]. The most significant structural feature of the MAGE proteins is in a large central MAGE homology domain flanked by variable amino- and carboxy-terminal domains [65].…”

“…The most critical biological consequences of Necdin are its negative impact on cell proliferation and its anti-angiogenic activity [65]. Necdin functions as a potent transcriptional repressor either through direct binding with DNA at guanosine clusters within the promoter region of target genes or through its interaction with other major transcription factors, including p53, E2F1 and Hif-1α [58,64,66]. It has also been reported that EBV-transformed B lymphocytes show a higher methylation status within the CpG islands of the Necdin promoter compared with primary lymphocytes [64].…”

Epstein–Barr virus nuclear antigen 3C regulated genes in lymphoblastoid cell lines

“…Furthermore, EBNA3C amino acids 365-545 or 724-826 repress or activate transcription when tethered to DNA by the Gal4 DNA binding domain (27,28). Moreover, EBNA3C interacts with other transcription factors or regulators, including HDAC1, CtBP, SMN, DP103, p300, prothymosin alpha, Sin3A, NcoR, and NECDIN (29)(30)(31)(32)(33)(34)(35).…”