Altered expression of the ER-resident aminopeptidases ERAP1 and ERAP2 might play an important role in shaping the MHC class I-presented peptide repertoire, but their function in tumors has not been determined in detail. Thus, the expression of ERAP1, ERAP2 and HLA class I heavy chain (HC) was analysed in various renal tumor types and corresponding kidney parenchyma by immunohistochemistry. Additionally, comparative expression profilings of untreated versus interferon (IFN)-γ-treated RCC cell lines were performed applying qRT-PCR, Western blot and/or flow cytometry. Normal kidney tissues showed strong ERAP1 staining in the proximal tubules of 57.4 % of cases, in the distal tubules of 94.3 % of cases and in the medulla of 88.6 % of cases, whereas high ERAP2 levels were observed in the medulla of 77.1 % of cases and in both, proximal and distal tubules of about 88 % of cases. Imbalanced, downregulated and RCC subtype-specific ERAP1 or ERAP2 expression was detected in 12.7 % or 43.8 % of samples analyzed, respectively. A coordinated downregulation of ERAPs was found in 4.8 %, an upregulation of ERAP1 or ERAP2 in 22.8 % or 2.0 % of RCC lesions. No association exists between ERAP and HLA class I HC expression for any tissue type. A heterogeneous constitutive ERAP expression pattern was also detected in RCC cell lines with lower ERAP2 than ERAP1 expression levels, which was in 11/17 RCC cell lines inducible by IFN-γ. Conclusively, ERAP1 and ERAP2 might be involved in the development of immune escape mechanisms of RCC.
Keywords: ERAP; HLA class I; Renal cell carcinoma; immune escape.