Valproic acid upregulates NKG2D ligand expression and enhances susceptibility of human renal carcinoma cells to NK cell-mediated cytotoxicity

INTRODUCTION We aimed to investigate the effect of valproic acid (VPA) on NKG2D ligand expression in human renal carcinoma cell lines and to investigate the mechanisms. MATERIAL AND METHODS Different concentrations of VPA from 0.5 mM to 8.0 mM were applied to 786-O and ACHN cell lines, respectively. Cell viability after treatment with VPA was determined by flow cytometry (FCM). Real-time PCR and FCM were used to detect the changes of mRNA and protein level of NKG2D ligands (MICA/B and ULBPs) in the two cell lines treated with 4 mM VPA. The cytotoxicity assay and CD107a mobilization assay were carried out to detect the cytotoxicity changes of NK cells against renal carcinoma cell lines after the same treatment. RESULTS Valproic acid can efficiently upregulate MICA/B, ULBP1 and ULBP2 expression in the renal carcinoma cell lines at the mRNA and protein level (p < 0.05). 786-O and ACHN cells treated with VPA were more susceptible to killing by NK cells than untreated cells and the enhanced cytotoxicity of NK cells was blocked by the pretreatment of NK cells with anti-NKG2D monoclonal antibodies (p < 0.05). CONCLUSIONS Valproic acid can clearly induce the expression of NKG2D ligands of renal carcinoma cell lines, thereby enhancing the cytotoxicity of NK cells against renal carcinoma cell lines.