Department of Hepatobiliary Surgery, The First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, China.
Center for Translational Medicine, The First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, China.
Cancer Immunol Immunother. 2023 Dec;72(12):4279-4292. doi: 10.1007/s00262-023-03563-8. Epub 2023 Oct 31.
Bcl-2-associated transcription factor-1 (BCLAF1), an apoptosis-regulating protein of paramount significance, orchestrates the progression of various malignancies. This study reveals increased BCLAF1 expression in hepatocellular carcinoma (HCC) patients, in whom elevated BCLAF1 levels are linked to escalated tumor grades and diminished survival rates. Moreover, novel BCLAF1 expression is particularly increased in HCC patients who were not sensitive to the combined treatment of atezolizumab and bevacizumab, but not in patients who had tumors that responded to the combined regimen. Notably, overexpression of BCLAF1 increases HCC cell proliferation in vitro and in vivo, while the conditioned medium derived from cells overexpressing BCLAF1 strikingly enhances the tube-formation capacity of human umbilical vein endothelial cells. Furthermore, compelling evidence demonstrates that BCLAF1 attenuates the expression of prolyl hydroxylase domain protein 2 (PHD2) and governs the stability of hypoxia-inducible factor-1α (HIF-1α) under normoxic conditions without exerting any influence on transcription, as determined by Western blot and RT‒qPCR analyses. Subsequently, employing coimmunoprecipitation and immunofluorescence, we validated the reciprocal interaction between BCLAF1 and Cullin 3 (CUL3), through which BCLAF1 actively upregulates the ubiquitination and degradation of PHD2. The Western blot and RT‒qPCR results suggests that programmed death ligand-1 (PD-L1) is one of the downstream responders to HIF-1α in HCC. Thus, we reveal the pivotal role of BCLAF1 in promoting PD-L1 transcription and, through binding to CUL3, in promoting the accumulation of HIF-1α under normoxic conditions, thereby facilitating the ubiquitination and degradation of PHD2.
Bcl-2 相关转录因子-1（BCLAF1）是一种重要的凋亡调节蛋白，可调控多种恶性肿瘤的进展。本研究揭示了肝癌（HCC）患者中 BCLAF1 表达增加，BCLAF1 水平升高与肿瘤分级升高和生存率降低有关。此外，新型 BCLAF1 表达在对阿特珠单抗和贝伐珠单抗联合治疗不敏感的 HCC 患者中特别增加，但在对联合方案有反应的肿瘤患者中没有增加。值得注意的是，BCLAF1 的过表达可增加 HCC 细胞的体外和体内增殖，而过表达 BCLAF1 的细胞条件培养基可显著增强人脐静脉内皮细胞的管形成能力。此外，有力的证据表明，BCLAF1 在常氧条件下可减弱脯氨酰羟化酶结构域蛋白 2（PHD2）的表达，并调控缺氧诱导因子-1α（HIF-1α）的稳定性，而不会通过 Western blot 和 RT‒qPCR 分析对转录产生任何影响。随后，通过免疫共沉淀和免疫荧光，我们验证了 BCLAF1 与 Cullin 3（CUL3）之间的相互作用，BCLAF1 通过该作用可积极上调 PHD2 的泛素化和降解。Western blot 和 RT‒qPCR 结果表明，程序性死亡配体-1（PD-L1）是 HCC 中 HIF-1α 的下游反应之一。因此，我们揭示了 BCLAF1 在促进 PD-L1 转录中的关键作用，以及通过与 CUL3 结合，在常氧条件下促进 HIF-1α 的积累，从而促进 PHD2 的泛素化和降解。
