Presence of simian virus 40 DNA sequences in diffuse large B-cell lymphomas in Tunisia correlates with aberrant promoter hypermethylation of multiple tumor suppressor genes

Abstract

The simian virus SV40 (SV40), a potent DNA oncogenic polyomavirus, has been detected in several human tumors including lymphomas, mainly in diffuse large B-cell type (DLBCL). However, a causative role for this virus has not been convincingly established. Hypermethylation in promoter regions is a frequent process of silencing tumor suppressor genes (TSGs) in cancers, which may be induced by oncogenic viruses. In this study, we investigated the relationship between the presence of SV40 DNA sequences and the methylation status of 13 TSGs in 108 DLBCLs and 60 nontumoral samples from Tunisia. SV40 DNA presence was investigated by PCR assays targeting the large T-antigen, the regulatory and the VP1 regions. Hypermethylation was carried out by methylation-specific PCR. SV40 DNA was detected in 63/108 (56%) of DLBCL and in 4/60 (6%) of nontumoral samples. Hypermethylation frequencies for the tested TSGs were 74% for DAPK, 70% for CDH1, SHP1, and GSTP1, 58% for p16, 54% for APC, 50% for p14, 39% for p15, 19% for RB1, 15% for BLU, 3% for p53, and 0% for p300 and MGMT. No hypermethylation was observed in nontumoral samples. Hypermethylation of SHP1, DAPK, CDH1, GSTP1 and p16 genes were significantly higher in SV40-positive than in SV40-negative DLBCL samples (p values ranging from 0.0006 to <0.0001). Our findings showed a high prevalence of SV40 DNA in DLBCLs in Tunisia. The significant association of promoter hypermethylation of multiple TSGs with the presence of SV40 DNA in DLBCLs supports a functional effect of the virus in those lymphomas.