Expression And Role Of Mica In Human Hepatocellular Carcinoma

OBJECTIVEMICA and MICB, as components of innate immune system, play a role in tumor immune surveillance via interation with NKG2D.Our previous study indicated that 5-aza-dC ,a kind of methylase inhibitor ,induced MICB expression in a DNA damage-dependent manner, which in turn sensitized tumor cells to NKL-cell-mediated lysis. RNAi acts constitutively to silence the innate immune response, and innate immunity genes are misregulated in Dicer-deficient Caenorhabditis elegans. Here we will determine the expression level of MICA in HepG2 cells (an HCC cell line) and L02 cells ( a normal liver cell) , and investigate the effect of 5-aza-dC or Dicer knockdown on MICA expression in HepG2 cells. Furthermore, we will detect the expressions of MICA and Dicer in HCC.METHODS1. HepG2 cells were treated with 5-aza-dC, caffeine , ATM-specific siRNA or Dicer-specific siRNA. The cell surface MICA protein on HepG2 and L02 cells were determined using flow cytometry. The mRNA levels were detected using real time RT-PCR. Theγ-H2AX levels were examined by Immuno?uorescence microscopy.2. The mRNA levels of MICA and Dicer in 36 paired cancerous and corresponding adjacent non-neoplastic tissues from 36 HCC patients undergoing surgery were detected using real time RT-PCR. Furthermore, the mRNA levels of MICA and Dicer in cancerous tissues were analyzed respectively to clinical features including age, sex, tumor size, tumor metastasis status, tumor number and stage.RESULTS1.MICA was undetectable on the surface of L02 cells, but was highly expressed on HepG2 cells. MICA expression in HepG2 cell was upregulated in response to 5-aza-dC treatment or Dicer siRNA , and the upregulation of MICA was partially prevented by pharmacological or genetic inhibition of ataxia telangiectasia mutated (ATM) kinase.2.Dicer mRNA level was significantly lower in malignant tissues than in the corresponding non-neoplastic tissues in 36 HCC patients. There was no significance on MICA mRNA levels between malignant tissues and the corresponding non-neoplastic tissues in 36 HCC patients. Neither the Dicer nor MICA level was associated with clinical characteristics including age, sex, tumor number, tumor size, tumor stage, or distant metastasis in HCC cases.CONCLUSIONSOur data suggest that 5-aza-dC or Dicer loss induces the expression of MICA by a ATM-dependent DNA damage pathway, and RNAi mechanism may contribute to innate immune system on tumor immune surveillance.