High Mobility Group Box 1 Protein Is Methylated and Transported to Cytoplasm in Clear Cell Renal Cell Carcinoma

Background:The high mobility group box 1 (HMGB1) protein is a widespread nuclear protein present inmost cell types. It typically locates in the nucleus and functions as a nuclear cofactor in transcription regulation.However, HMGB1 can also localize in the cytoplasm and be released into extracellular matrix, where it playscritical roles in carcinogenesis and inflammation. However, it remains elusive whether HMGB1 is relocated tocytoplasm in clear cell renal cell carcinoma (ccRCC).
Methods: Nuclear and cytoplasmic proteins were extractedby different protocols from 20 ccRCC samples and corresponding adjacent renal tissues. Western blotting andimmunohistochemistry were used to identify the expression of HMGB1 in ccRCC. To elucidate the potentialmechanism of HMGB1 cytoplasmic translocation, HMGB1 proteins were enriched by immunoprecipitation andanalyzed by mass spectrometry (MS).
Results: The HMGB1 protein was overexpressed and partially localizedin cytoplasm in ccRCC samples (12/20, 60%, p<0.05). Immunohistochemistry results indicated that ccRCCof high nuclear grade possess more HMGB1 relocation than those with low grade (p<0.05). Methylation ofHMGB1 at lysine 112 in ccRCC was detected by MS. Bioinformatics analysis showed that post-translationalmodification might affect the binding ability to DNA and mediate its translocation.
Conclusion: Relocation ofHMGB1 to cytoplasm was confirmed in ccRCC. Methylation of HMGB1 at lysine 112 might the redistributionof this cofactor protein.