Methylation of the CpG island of SNK/PLK2 but not FNK/PRK/PLK3 in B-cell neoplasia. Methylation-specific PCR (MSP) was performed as described in “Materials and methods” and PCR products resolved on 2% agarose gels. (A) The SNK/PLK2 CpG island is fully methylated in BL cell lines that lack expression of the gene, but completely unmethylated in EBV-immortalized LCLs that express Snk/Plk2. U indicates unmethylated; M, methylated. The toppanel is BL cells lines; the bottom panel, LCLs. The identity of each cell line is shown above the gel. Specificity controls are denoted C1 (control unmethylated DNA) and C2 (control methylated DNA). (B) The CpG island in the FNK/PRK/PLK3 promoter is completely unmethylated in BL. The top panel is BL cells lines; the bottom panel, LCLs. The identity of each cell line is shown above the gel. (C) Demethylation of the SNK/PLK2 CpG island reverses transcriptional silencing. BL lines positive (Rael) and negative (DG75) for EBV and lacking expression of Snk/Plk2 mRNA were exposed to demethylating agents and analyzed by RT-PCR as described in “Materials and methods.” Lanes are: 1 and 7, untreated; 2 and 8, 5 μM 5′AZA; 3 and 9, 10 μM 5′AZA; 4 and 10, 300 μM TSA; 5 and 11, 5 μM 5′AZA plus 300 μM TSA; 6 and 12, 10 μM 5′AZA plus 300 μM TSA.