PTPRK expression is down-regulated by EBV infection or expression of EBNA1 in Hodgkin lymphoma cells. (A) Heat map showing genes differentially expressed in the presence of EBV in both L591 and KM-H2 cells. Twelve genes were up-regulated and 2 genes down-regulated in both HL cell lines in the presence of EBV. Down-regulated genes included PTPRK, a putative tumor-suppressor gene. L591-SD3 is an EBV-negative variant of the EBV-positive parental L591 line. KM-H2-EBV is an EBV-positive HL cell line generated by infection of EBV-negative KM-H2 cells with recombinant Akata-derived EBV. (B) Semiquantitative RT-PCR for PTPRK shows lower levels of PTPRK mRNA in EBV-positive L591 and KM-H2 cells compared with their EBV-negative counterparts (L591-SD3 and KM-H2-neo, respectively). Immunoblotting demonstrates the down-regulation of PTPRK protein in EBV-positive HL cells compared with their EBV-negative counterparts. KM-H2 neo is a control cell line generated by the transfection of EBV-negative KM-H2 cells with a plasmid containing a neomycin resistance gene. (C left panel) RT-PCR analysis of EBV-negative KM-H2 cells transfected with EBNA1 reveals that expression of EBNA1 is sufficient to reduce PTPRK mRNA expression. No other EBV latent gene affected PTPRK expression (data not shown). (C right panel) RT-PCR analysis demonstrates that transient transfection of the EBV-negative HL cell line, HDLM-2, with EBNA1 also results in the down-regulation of PTPRK expression. Similar results were observed following ectopic EBNA1 expression in the EBV-negative HL cell line L428 (data not shown).