Key Laboratory of Pathogen Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China.
University of Chinese Academy of Science, Beijing 100049, China.
J Mol Cell Biol. 2023 Nov 27;15(5). doi: 10.1093/jmcb/mjad027.
Alpha-fetoprotein (AFP) is the most widely used biomarker for the diagnosis of hepatocellular carcinoma (HCC). However, a substantial proportion of HCC patients have either normal or marginally increased AFP levels in serum, and the underlying mechanisms are not fully understood. In the present study, we provided in vitro and in vivo evidence that heat shock protein gp96 promoted AFP expression at the transcriptional level in HCC. NR5A2 was identified as a key transcription factor for the AFP gene, and its stability was enhanced by gp96. A further mechanistic study by co-immunoprecipitation, GST pull-down, and molecular docking showed gp96 and the SUMO E3 ligase RanBP2 competitively binding to NR5A2 at the sites spanning from aa 507 to aa 539. The binding of gp96 inhibited SUMOylation, ubiquitination, and subsequent degradation of NR5A2. In addition, clinical analysis of HCC patients indicated that gp96 expression in tumors was positively correlated with serum AFP levels. Therefore, our study uncovered a novel mechanism that gp96 regulates the stability of its client proteins by directly affecting their SUMOylation and ubiquitination. These findings will help in designing more accurate AFP-based HCC diagnosis and progression monitoring approaches.
甲胎蛋白（AFP）是诊断肝细胞癌（HCC）最常用的生物标志物。然而，相当一部分 HCC 患者的血清 AFP 水平正常或略有升高，其潜在机制尚不完全清楚。在本研究中，我们提供了体外和体内证据，表明热休克蛋白 gp96 在 HCC 中以转录水平促进 AFP 的表达。NR5A2 被鉴定为 AFP 基因的关键转录因子，其稳定性被 gp96 增强。通过免疫共沉淀、GST 下拉和分子对接的进一步机制研究表明，gp96 和 SUMO E3 连接酶 RanBP2 在跨越 aa507 至 aa539 的位点上竞争结合 NR5A2。gp96 的结合抑制了 NR5A2 的 SUMO 化、泛素化和随后的降解。此外，对 HCC 患者的临床分析表明，肿瘤中 gp96 的表达与血清 AFP 水平呈正相关。因此，我们的研究揭示了一种新的机制，即 gp96 通过直接影响其客户蛋白的 SUMO 化和泛素化来调节其稳定性。这些发现将有助于设计更准确的基于 AFP 的 HCC 诊断和进展监测方法。
