C-Myc and EBV-LMP1: Two opposing regulators of the HLA class i antigen presentation machinery in epithelial cells

Abstract

Background: Epstein-Barr virus (EBV)-encoded latent membrane protein 1 (LMP1) up-regulates the human leukocyte antigen (HLA) class I antigen presentation machinery (APM). This appears counterintuitive with immune evasion in EBV-associated tumours like nasopharyngeal carcinoma (NPC). Methods: Latent membrane protein 1-transfected epithelial cell lines were used as a model system to study the impact of LMP1 and c-Myc on HLA class I components. The expression of components of the HLA class I APM, c-Myc and Ki-67 was analysed in LMP1 and LMP1 NPC by immunohistochemistry. Results: In epithelial cells, LMP1 up-regulated HLA class I APM. This effect could be counteracted by c-Myc, which itself was up-regulated by LMP1 apparently through IL6 induction and Jak3/STAT3 activation. Studies of NPC biopsies revealed down-regulation of HLA class I APM expression. No difference was observed between LMP1 and LMP1 NPC. However, expression of Ki-67 and c-Myc were up-regulated in LMP1 tumours. Conclusion: These findings raise the possibility that c-Myc activation in NPC might antagonise the effect of LMP1 on HLA class I expression thus contributing to immune escape of tumour cells. © 2012 Cancer Research UK All rights reserved.