EBV latent
membrane protein 1 (LMP1) activates cellular
DNA methyltransferases, resulting in hypermethylation and silencing of
E-cadherin. However, the underlying mechanism remains to be elucidated. In this study, we show that LMP1 directly induces the dnmt1 promoter activity through its COOH-terminal activation region-2 YYD domain. Using (i) LMP1 mutants, (ii) dominant negative mutants c-jun NH(2)-terminal
kinase (JNK)-DN, p38-DN, and constitutive active mutant IkappaB, as well as (iii) dsRNAs targeting c-Jun, JNK, and
tumor necrosis factor receptor-associated death domain
protein, and (iv) signal transduction inhibitors, we show that LMP1-mediated
DNA methyltransferase-1 (DNMT1) activation involves JNK but not
nuclear factor kappaB and
p38/mitogen-activated protein kinase signaling. In addition, LMP1 is unable to activate dnmt1-P1 promoter with
activator protein-1 (AP-1) site mutation.
Chromatin immunoprecipitation assay results also confirm that LMP1 activates P1 promoter via the JNK-AP-1 pathway. Furthermore,
chromatin immunoprecipitation assay data in LMP1-inducible cells disclose that LMP1 induces formation of a transcriptional repression complex, composed of DNMT1 and
histone deacetylase, which locates on
E-cadherin gene promoter. Treatment with JNK inhibitor,
SP600125, prevents the formation of this repression complex. Statistical analyses of the immunohistochemical staining of 32
nasopharyngeal carcinoma (NPC) biopsies show LMP1 expression (18 of 32, 56.25%), DNMT1 expression (31 of 32, 97%), and phospho-c-Jun (27 of 32, 84.38%), suggesting that overexpression of these
proteins is observed in NPC
tumor. Overall, these results support a mechanistic link between JNK-AP-1 signaling and DNA methylation induced by the EBV
oncogene product LMP1.