Knockdown of PTPRK expression in EBV-negative KM-H2 cells increases the growth and survival of HL cells. (A) Semiquantitative RT-PCR for PTPRK mRNA (top) and immunoblotting for PTPRK protein (bottom) following siRNA-mediated knockdown of PTPRK expression in EBV-negative KM-H2 cells. (B) Cell viability (trypan blue; left) and cell proliferation (WST-1; right) assays on KM-H2 cells following treatment with PTPRK-specific siRNA. The down-regulation of PTPRK expression in these cells results in a significant increase in cell viability and proliferation (* denotes significant difference; P values are .02 for viability and .003 for proliferation). Transfection with irrelevant siRNA oligonucleotides had no effect on PTPRK expression, cell viability, or proliferation (data not shown).