microRNA 125a Regulates MHC-I Expression on Esophageal Adenocarcinoma Cells, Associated With Suppression of Antitumor Immune Response and Poor Outcomes of Patients.

BACKGROUND & AIMS: Immune checkpoint inhibition may affect growth or progression of highly aggressive cancers, such as esophageal adenocarcinoma (EAC). We investigated the regulation of expression of major histocompatibility complex, class 1 (MHC-I) proteins (encoded by HLA-A, HLA-B, and HLA-C) and the immune response to EACs in patient samples. METHODS: We performed quantitative polymerase chain reaction array analyses of OE33 cells and OE19 cells, which express different levels of the ATP binding cassette subfamily B member 1 (TAP1) and TAP2, required for antigen presentation by MHC-I, to identify microRNAs (miRNAs) that regulate their expression. We performed luciferase assays to validate interactions between miRNAs and potential targets. We overexpressed candidate miRNAs in OE33, FLO-1, and OACP4 C cell lines and performed quantitative polymerase chain reaction, immunoblot, and flow cytometry analyses to identify changes in messenger RNA (mRNA) and protein expression; we studied the effects of cytotoxic T cells. We performed miRNA in situ hybridization, RNA-sequencing, and immunohistochemical analyses of tumor tissues from 51 untreated patients with EAC in the Netherlands. Clinical and survival data were collected for patients, and EAC subtypes were determined. RESULTS: We found OE19 cells to have increased levels of 7 miRNAs. Of these, we found binding sites for miRNA 125a (MIR125a)-5p in the 3' untranslated region of the TAP2 mRNA and binding sites for MIR148a-3p in 3' untranslated regions of HLA-A, HLA-B, and HLA-C mRNAs. Overexpression of these miRNAs reduced expression of TAP2 in OE33, FLO-1, and OACP4 C cells, and reduced cell-surface levels of MHC-I. OE33 cells that expressed the viral peptide BZLF1 were killed by cytotoxic T cells, whereas OE33 that overexpressed MIR125a-5p or MIR 148a along with BZLF1 were not. In EAC and nontumor tissues, levels of MIR125a-5p correlated inversely with levels of TAP2 protein. High expression of TAP1 by EAC correlated with significantly shorter overall survival times of patients. EACs that expressed high levels of TAP1 and genes involved in antigen presentation also expressed high levels of genes that regulate the adaptive immune response, PD-L1, PD-L2, and IDO1; these EACs had a poor response to neoadjuvant chemoradiotherapy and associated with shorter overall survival times of patients. CONCLUSIONS: In studies of EAC cell lines and tumor tissues, we found increased levels of MIR125a-5p and MIR148a-3p to reduce levels of TAP2 and MHC-I, required for antigen presentation. High expression of MHC-I molecules by EAC correlated with markers of an adaptive immune response and significantly shorter overall survival times of patients.