Post-Transcriptional and Epigenetic Regulation of Antigen Processing Machinery (APM) Components and HLA-I in Cervical Cancers from Uighur Women

Ayshamgul Hasim,Zhen Jiao,Reshalaiti Aimiduo,Ting Wang,Abulizi Abudula,Mangnishahan Abudula,Mangnishahan Abudula,Gulzareye Akula,Jun-Qi Ma,Torbjörn Ramqvist

doi:10.1371/journal.pone.0044952

Abstract

Normal function of human leukocyte antigen class I (HLA-I) and antigen processing machinery (APM) proteins is required for T cell-mediated anti-tumor or antiviral immunity, whereas the tumor survival indicates a failure of the host in immune surveillance associated with the dysfunction in antigen presentation, mainly due to the deregulation in HLA-I and APM expression or function. The posttranscriptional regulation of HLA-I and APM expression may associate with epigenetic modifications in cancer development which was not described so far. Here we showed that the development of cervical intraepithelial neoplasia (CIN) and cervical squamous cell carcinoma (CSCC) in Uighur women was accompanied with the partial or total loss of protein expression of HLA-I, ß2-m and APM components, including the transporter associated with antigen processing (TAP1/2), low molecular mass protein (LMP2, LMP7), endoplasmic reticulum aminopeptidase 1(ERAP1), chaperone molecules include calreticulin (CLR), calnexin (CNX) and ERp57, and this was proved again by analysis of transcription of the same genes in addition to three genes HLA-A, B and C coding for HLA-I. By bisulfite sequencing approach, we identified target CpG islands methylated at the gene promoter region of TAP1, TAP2, LMP7, tapasin and ERp57 in cervical carcinoma cells. Further analysis of CpG site specific methylation of these genes in cases of CSCC and CIN demonstrated an inverse correlation of altered CpG island methylation of TAP1, LMP7, and ERp57 with changes in protein expression. Moreover, promoter methylation of these genes was significantly higher in cases positive for human papillomavirus 16 (HPV 16) than negative ones. Our results suggested that epigenetic modifications are responsible for the aberrant expression of certain HLA-I and APM genes, and may help to understand unrevealed mechanisms of tumor escape from immune surveillance in cervical carcinogenesis.

Highlights

The formation and survival of a tumor cell is a sign of successful immune escape and a failure in host immune surveillance and elimination
Of the 64 cases cervical intraepithelial neoplasia (CIN) and the 63 cases cervical squamous cell carcinoma (CSCC) enrolled in this study (Table I and Figure 2), the protein expression level of HLA class I and antigen processing machinery (APM) components was altered from normal expression to partial loss or total loss, with the development of normal epithelium of uterine cervix to CIN and CSCC
The partial loss of protein expression of human leukocyte antigen class I (HLA-I), ß2-m, TAP1, TAP2, LMP2, LMP7, endoplasmic reticulum aminopeptidase 1 (ERAP1), tapasin and ERp57 was statistically significant for CIN cases compared to normal controls

Summary

Introduction

The formation and survival of a tumor cell is a sign of successful immune escape and a failure in host immune surveillance and elimination. Normal function of human leukocyte antigen class I (HLA-I) and antigen processing machinery (APM) is a prerequisite for T cell-mediated innate and adaptive immune responses against viral infection or cellular carcinogenesis [1,2,3]. Progress has been made in understanding how peptides presented by HLA-I molecules. It is known which proteases are involved and how intracellular pathways influence antigen presentations in professional antigen presenting cells and in various types of malignant disease [6,7,8]. The thiol oxidoreductase ERp57 is responsible for presentation of HLA-I peptide complexes on the cell surface and is crucial for recognition of virally infected or malignantly transformed cells, maintenance of self-tolerance, and surveillance of newly arising tumors by the immune system [9]. Downregulation of HLA-I expression caused by hypermethylation of HLA-I genes has been documented in esophageal squamous cell carcinoma, colon carcinoma, and melanoma cell lines, and this could be reversed upon treatment with DNA methyltransferase inhibitors [10,11]

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