Frequent Hypermethylation of RASSF1A, TSLC1, High Viral Load of Epstein-Barr Virus DNA in Nasopharyngeal Carcinoma, Matched Tumor-Adjacent Tissues

Abstract

We examined the promoter hypermethylation of tumor-suppressor genes RASSF1A and TSLC1, quantitated EBV DNA load in nasopharyngeal carcinoma (NPC) tissues (T tissues), and matched tumor-adjacent tissues outside 0.5 cm (P tissues) and outside 1.0 cm (Z tissues) to evaluate the role of promoter hypermethylation of RASSF1A and TSLC1 as well as viral load in the pathogenesis of NPC. Methylation-specific polymerase chain reaction (PCR) for RASSF1A and TSLC1 and quantitative real-time PCR analysis of EBV DNA were performed on matched T, P, and Z tissues (n = 28) as well as chronic nasopharyngitis tissues (n = 8). Hypermethylated RASSF1A was frequently detected in the T (82%) and P tissues (75%), but less frequently in Z tissues (46%). he average quantities of EBV DNA (copies/microg DNA) in matched T, P, and Z tissues were 673,000, 90,000, and 7000. The differences of promoter hypermethylation of RASSF1A and EBV viral load among T, P, and Z tissues were statistically significant, with more frequent methylation and higher viral load detected when tissues examined were nearer to the NPC tissues. Our results suggest that aberrant hypermethylation of RASSF1A and high EBV load might be important events in NPC pathogenesis, and they may be useful molecular diagnostic markers for this cancer.

Epigenetic silencing of a Ca 2+ -regulated Ras GTPase-activating protein RASAL defines a new mechanism of Ras activation in human cancers

“…A number of tumor cell lines and DNA/RNA samples of primary tumors (carcinomas of nasopharynx, breast, lung, liver, esophagus and kidney, and nasal NK/T cell lymphoma), and their corresponding normal tissues were used in this study, as described (25,(45)(46)(47)(48)(49)(50)(51)(52).…”

The major 8p22 tumor suppressor DLC1 is frequently silenced by methylation in both endemic and sporadic nasopharyngeal, esophageal, and cervical carcinomas, and inhibits tumor cell colony formation

“…DNA and RNA samples were extracted from 68 primary endemic NPC (Southern China and Southeast Asia Chinese), 14 Asian Chinese breast carcinomas (Tao et al, 1998(Tao et al, , 1999Murray et al, 2004;Qiu et al, 2004;Ying et al, 2005;Zhou et al, 2005), eight cervical carcinomas (Steenbergen et al, 2004), and three normal nasopharyngeal tissues (Srivastava et al, 2000). We also collected four sporadic Caucasian NPC from the Department of Otolaryngology-Head and Neck Surgery, John Hopkins Hospital, Baltimore, which together with three nude mice-passaged undifferentiated NPC tumors derived from North Africans (C15, C17, C18) (Busson et al, 1988), acted as comparison for the endemic type NPC from Southern China and Southeast Asia.…”

“…Genetic mutations of known TSGs, including TP53 and RB1, are infrequent in NPC (Effert et al, 1992;Spruck, III et al, 1992;Sun et al, 1992). Meanwhile, epigenetic abnormalities, alone or together with genetic alterations, have been shown to be frequently involved in NPC, such as the promoter methylation of BLU and RASSF1A at 3p21 Zhou et al, 2005), TSLC1 on 11q (Hui et al, 2003), GADD45G on 9q22 (Ying et al, 2005) and PCDH10 (Ying et al, 2006). These limited findings suggest that additional cancer-related genes are yet to be identified in NPC in the reported regions, or in other unidentified loci.…”

An Update on Epstein-Barr Virus and Nasopharyngeal Carcinogenesis

“…3p and 9p abnormalities have been identified in low-grade dysplastic lesions and normal nasopharyngeal mucosa of individuals at high risk indicating that these genetic changes are early events in the pathogenesis of NPC [10,17,20,33]. Other genes frequently inactivated by promoter methylation in NPC include TSCL1 at 11q23 and EDNRB at 13q22, E-cadherin, and death-associated protein kinase (DAPK) [34][35][36]. Gene expression profiling has shown dysregulation of the PI3K/Akt, WNT/b-catenin, TGF-b, and MAPK signaling pathways in NPC with upregulation of NF-jB2, survivin, Bcl-2 upregulation, nuclear accumulation of bcatenin, and dysregulation of integrins [37].…”