title: Synergistic enhancement of NK cell-mediated cytotoxicity by combination of histone deacetylase inhibitor and ionizing radiation.
abstract: BACKGROUND
  The overexpression of histone deacetylase (HDAC) and a subsequent decrease in the acetylation levels of nuclear histones are frequently observed in cancer cells. Generally it was accepted that the deacetylation of histones suppressed expression of the attached genes. Therefore, it has been suggested that HDAC might contribute to the survival of cancer cells by altering the NKG2D ligands transcripts. By the way, the translational regulation of NKG2D ligands remains unclear in cancer cells. It appears the modulation of this unclear mechanism could enhance NKG2D ligand expressions and the susceptibility of cancer cells to NK cells. Previously, it was reported that irradiation can increase the surface expressions of NKG2D ligands on several cancer cell types without increasing the levels of NKG2D ligand transcripts via ataxia telangiectasia mutated and ataxia telangiectasia and Rad3 related (ATM-ATR) pathway, and suggested that radiation therapy might be used to increase the translation of NKG2D ligands.
  
  
  METHODS
  Two NSCLC cell lines, that is, A549 and NCI-H23 cells, were used to investigate the combined effects of ionizing radiation and HDAC inhibitors on the expressions of five NKG2D ligands. The mRNA expressions of the NKG2D ligands were quantitated by multiplex reverse transcription-PCR. Surface protein expressions were measured by flow cytometry, and the susceptibilities of cancer cells to NK cells were assayed by time-resolved fluorometry using the DELFIA® EuTDA cytotoxicity kit and by flow cytometry.
  
  
  RESULTS
  The expressions of NKG2D ligands were found to be regulated at the transcription and translation levels. Ionizing radiation and HDAC inhibitors in combination synergistically increased the expressions of NKG2D ligands. Furthermore, treatment with ATM-ATR inhibitors efficiently blocked the increased translations of NKG2D ligands induced by ionizing radiation but did not block the increased ligand translations induced by HDAC inhibitors. The study confirms that increased NKG2D ligand levels by ionizing radiation and HDAC inhibitors could synergistically enhance the susceptibilities of cancer cells to NK-92 cells.
  
  
  CONCLUSIONS
  This study suggests that the expressions of NKG2D ligands are regulated in a complex manner at the multilevel of gene expression, and that their expressions can be induced by combinatorial treatments in lung cancer cells.
authors: Department of Biochemistry, Pusan National University School of Medicine, Yangsan 626-870, South Korea. 75dokdo@naver.com.
authors: Cheol-Hun
authors: CH
authors: Son
authors: Jin-Hee
authors: JH
authors: Keum
authors: Kwangmo
authors: K
authors: Yang
authors: Jiho
authors: J
authors: Nam
authors: Mi-Ju
authors: MJ
authors: Kim
authors: Sun-Hee
authors: SH
authors: Kim
authors: Chi-Dug
authors: CD
authors: Kang
authors: Sae-Ock
authors: SO
authors: Oh
authors: Chi-Dae
authors: CD
authors: Kim
authors: You-Soo
authors: YS
authors: Park
authors: Jaeho
authors: J
authors: Bae
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000473:pathology / Q000628:therapy; D002478:Cells, Cultured; D003131:Combined Modality Therapy; D003602:Cytotoxicity, Immunologic / Q000187:drug effects / Q000528:radiation effects; D004357:Drug Synergism; D015870:Gene Expression / Q000187:drug effects / Q000528:radiation effects; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D006801:Humans; D007694:Killer Cells, Natural / Q000276:immunology*; D008024:Ligands; D008175:Lung Neoplasms / Q000473:pathology / Q000628:therapy; D055655:NK Cell Lectin-Like Receptor Subfamily K / Q000378:metabolism; D011836:Radiation Tolerance / Q000187:drug effects / Q000235:genetics; D011839:Radiation, Ionizing; D015854:Up-Regulation / Q000187:drug effects / Q000528:radiation effects
chemical_list: D056572:Histone Deacetylase Inhibitors; D008024:Ligands; D055655:NK Cell Lectin-Like Receptor Subfamily K