| [Background and objective]:Esophageal squamous cell carcinoma (ESCC) is a very aggressive disease with a poor prognosis. Despite aggressive treatment modalities such as surgical tumor resection with extensive lymphadenectomy and chemo-radiation therapy, only20-36%of them survive at5years. In recent year immunotherapy such as the utilization of anti-tumor T cells or antibodies induced by cancer vaccination has become an attractive option for the revival of the role of immune surveillance in the control of tumor growth. It is well known that HLA class I molecules are critical for the presentation of antigen peptides, including those derived from tumor cells, to cytotoxic T lymphocytes and the downregulation of HLA class I on the tumor allows it to evade cytotoxic T lymphocytes-mediated anti-tumor immunity, leading to variant cancer cells that arise from the parent tumor during tumor progression at both primary and metastatic sites. Loss of HLA class I antigen expression can occur at the genetic, transcriptional and post-transcriptional levels. DNA methylation, especially5-CPG methylation, is an important mechanism in silencing the expression of genes. DNA methylation may directly interfere with the basal transcriptional machinery by altering the DNA secondary structure, especially the major groove conformation. DNA methylation can also induce chromosome remodeling through histone deacetylation, resulting in transcriptional repression. Those may suggest that the DNA hypermethylation shoud be an important role in the downregulation of HLA class I genes in ESCC. The HLA class I antigens, HLA-A, HLA-B and HLA-C, which form the class I major histocompatibility complex in humans, take part in the recognition of virally infected, grafted or transformed cells by cytotoxic T cells. The HLA genes are located on chromosome6p21and are expressed in most somatic tissues. Selective loss of expression of these loci has frequently been observed in human tumors and this event is thought to help tumor cells escape immune surveillance by T cells and natural killer cells. The downregulation of HLA class I has been observed in kidney, prostate, stomach, colon and germ cell testicular cancer and has been associated with tumor invasiveness and aggressiveness. In our study, we found that HLA class I was downregulated or even lost in78.2%of primary ESCC lesions, and was downregulated in87%of metastatic lymph nodes.This frequency in primary ESCC lesions is comparable to those reported in previous studies. Those studies and our results clearly showed that there is a marked reduction in the expression of HLA class I molecules in ESCC lesions. And in our studies, it showed that the reduction of HLA class I presentation was significantly associated with the metastasis, tumor grade and poor survival of the ESCC. This is also comparable to those reported in previous studies.Loss of HLA class I antigen expression can occur at the genetic, transcriptional and post-transcriptional levels. DNA methylation, especially5'-CpG methylation, is an important mechanism in silencing the expression of genes. DNA methylation may directly interfere with the basal transcriptional machinery by altering the DNA secondary structure, especially the major groove conformation. DNA methylation can also induce chromosome remodeling through histone deacetylation, resulting in transcriptional repression. A group of methyl-CpG-binding proteins, which preferentially bind to methylated CpG dinucleotides, may interact with sin3A. Sin3A in turn interacts with histone deacetylaseand is thought to be involed in this process. Abnormal DNA methylation has been found in various genes, including the putative tumor suppressor genes retinoblastoma and p16INK4A, leading to their downregulation in tumors. Costello et al. conducted a global examination of CpG methylation in a large group of tumors and observed tumor type-specific pattern. CpG islands are small regions of DNA ranging from0.5to4-5kb in length where the GC contents is>60%and the CpG:GpC ratio is>0.6. Using these criteria, we have conducted a search for well-preserved CpG islands in genes that have been reported to be inactivated high CpG:GpC ratios, as well as a GC content>60%. Hypermethylation of these genes has not been reported in either tumor or spermatogenic cells where HLA class I genes were not express.In this study, firstly we investigated HLA class I expression in primary and metastatic lesions in ESCC patients by immunohistochemistry. And secondly we investigated the methylation changes in the promoter region of HLA class I by using methylation-specific PCR. Furthermore, we evaluated the correlation between methylation of HLA class I and the clinicopathological status or the prognosis in patients with ESCC.[Material and methods]:A total of87formalin-fixed and paraffin-embeded ECSS lesions were collected. HLA-|and antigen-processing machinery component's expression were investigated by immunohistochemistry with anti-HLA class I monoclonal antibody and methylation changes in the promoter region of HLA-1genes were determined by using methylation-specific PCR.[Results]:HLA-|antigen,TAP1and LMP were lost or down-regulated in67,29.8and47.0%of the ESCC lesions, respectively. The positive rates of genes promoter hypermethylation of HLA-|was70.1%(61/87) in tumor tissues, as comparede to3.6%in normal tissue (p<0.01). And the higher methylation rates and the HLA-I expression were significantly associated with tumor grade, including the lymph node metastasis (p<0.05).[Conclusions]:HLA-|promoter hypermethylation was associated with loss of HLA-1antigen, which frequently occurred in primary tumor especially in metastatic lymph node lesions and was associated with patient prognosis. |
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