BCLAF1 binds SPOP to stabilize PD-L1 and promotes the development and immune escape of hepatocellular carcinoma.

Interaction between programmed death-1 (PD-1) ligand 1 (PD-L1) on tumor cells and PD-1 on T cells allows tumor cells to evade T cell-mediated immune surveillance. Strategies targeting PD-1/PD-L1 have shown clinical benefits in a variety of cancers. However, limited response rates in hepatocellular carcinoma (HCC) have prompted us to investigate the molecular regulation of PD-L1. Here, we identify B cell lymphoma-2-associated transcription factor 1 (BCLAF1) as a key PD-L1 regulator in HCC. Specifically, BCLAF1 interacts with SPOP, an E3 ligase that mediates the ubiquitination and degradation of PD-L1, thereby competitively inhibiting SPOP-PD-L1 interaction and subsequent ubiquitination and degradation of PD-L1. Furthermore, we determined an SPOP-binding consensus (SBC) motif mediating the BCLAF1-SPOP interaction on BCLAF1 protein and mutation of BCLAF1-SBC motif disrupts the regulation of the SPOP-PD-L1 axis. In addition, BCLAF1 expression was positively correlated with PD-L1 expression and negatively correlated with biomarkers of T cell activation, including CD3 and CD8, as well as with the level of immune cell infiltration in HCC tissues. Besides, BCLAF1 depletion leads to a significant reduction of PD-L1 expression in vitro, and this reduction of PD-L1 promoted T cell-mediated cytotoxicity. Notably, overexpression of BCLAF1 sensitized tumor cells to checkpoint therapy in an in vitro HCC cells-Jurkat cells co-culture model, whereas BCLAF1-SBC mutant decreased tumor cell sensitivity to checkpoint therapy, suggesting that BCLAF1 and its SBC motif serve as a novel therapeutic target for enhancing anti-tumor immunity in HCC.

Endometrial cancer (EC) derived G3BP1 overexpression and mutant promote EC tumorigenesis and metastasis via SPOP/ERα axis.

BACKGROUND: Ras-GTPase-activating protein binding protein 1 (G3BP1) is an oncogenic factor, which highly expressed in a variety of cancers. In recent years, G3BP1 has been reported to promote the development of prostate cancer by inhibiting the degradation of AR through inhibiting SPOP. However, whether G3BP1 contributes in a similar manner to the abnormal accumulation of ERα, which is also an important target for hormone therapy, remains unknown. This article addresses this issue and explores potential mechanisms. METHODS: Bioinformatics tools were used for G3BP1 expression analysis, survival analysis, and clinical association analysis. Immunohistochemical staining was used to examine the correlation between G3BP1 and ERα in EC patients. In addition, western blot and co-immunoprecipitation were used to detect the half-life of G3BP1 and mutant, and the effect of G3BP1 and mutant on the ubiquitination and degradation of ERα mediated by SPOP. Then, the oncogenic functions of G3BP1 dependent on the SPOP/ERα axis were determined by CCK8 cell proliferation assay, colony formation assay and cell migration assay. Finally, we established the EC cells treated or untreated with fulvestrant, exploring the possibility of fulvestrant combined with the reduction of G3BP1 to improve the efficacy of fulvestrant. RESULTS: G3BP1 is abnormally high expressed and characterized by high-frequency mutation in EC. In addition, there is a positive correlation between G3BP1 protein and ERα protein. Mechanistically, both G3BP1 and mutant, the latter is displaying the longer half-life, competitively bind SPOP with ERα, thereby inhibiting SPOP-mediated ubiquitination and degradation of ERα. Functionally, G3BP1 and mutant promote the proliferation and migration of EC cells by regulating the G3BP1/SPOP/ERα axis. However, fulvestrant can reverse the cancer-promoting effects of G3BP1 and mutant. CONCLUSIONS: G3BP1 and its mutant positively regulate ERα signaling pathway by inhibiting SPOP-mediated ubiquitination and degradation of ERα, indicating the promising effect of fulvestrant on the suppression the occurrence and development of EC with high expressed G3BP1 and G3BP1 mutants. Video Abstract.

The role of ubiquitination and deubiquitination in PI3K/AKT/mTOR pathway: A potential target for cancer therapy.

The PI3K/AKT/mTOR pathway controls key cellular processes, including proliferation and tumor progression, and abnormally high activation of this pathway is a hallmark in human cancers. The post-translational modification, such as Ubiquitination and deubiquitination, fine-tuning the protein level and the activity of members in this pathway play a pivotal role in maintaining normal physiological process. Emerging evidence show that the unbalanced ubiquitination/deubiquitination modification leads to human diseases via PI3K/AKT/mTOR pathway. Therefore, a comprehensive understanding of the ubiquitination/deubiquitination regulation of PI3K/AKT/mTOR pathway may be helpful to uncover the underlying mechanism and improve the potential treatment of cancer via targeting this pathway. Herein, we summarize the latest research progress of ubiquitination and deubiquitination of PI3K/AKT/mTOR pathway, systematically discuss the associated crosstalk between them, as well as focus the clinical transformation via targeting ubiquitination process.

FBXO7, a tumor suppressor in endometrial carcinoma, suppresses INF2-associated mitochondrial division.

Endometrial carcinoma (ECa) is the most common malignant gynecological cancer, with an increased incidence and fatality rate worldwide, while the pathogenesis is still largely unknown. In this study, we confirmed that FBXO7, a gene coding FBXO7 E3 ubiquitin ligase, is significantly downregulated and mutated (5.87%; 31/528) in ECa specimens, and the abnormal low expression and mutations of FBXO7 are associated with the occurrence of ECa. We also identify the excessive expression of INF2 protein, a key factor that triggers mitochondrial division by recruiting the DRP1 protein, and the elevated INF2 protein is significantly negatively correlated with the low FBXO7 protein in ECa specimens. Mechanistically, FBXO7 restrains ECa through inhibiting INF2-associated mitochondrial division via FBXO7-mediated ubiquitination and degradation of INF2. Moreover, we found that ECa-associated FBXO7 mutants are defective in the ubiquitination and degradation of INF2, promoting ECa cells proliferation, migration and apoptosis inhibition via inducing mitochondrial hyper-division. In addition, we found that it could reverse FBXO7 deletion or ECa-associated FBXO7 mutants-induced proliferation, migration, apoptosis inhibition and mitochondrial hyper-division of ECa cells by INF2 or DNM1L knockdown, or DRP1 inhibitor Mdivi-1. In summary, our study shows that FBXO7 acts as a novel tumor suppressor in ECa by inhibiting INF2-DRP1 axis-associated mitochondrial division through the ubiquitination and degradation of INF2 while the effect is destroyed by ECa-associated FBXO7 and INF2 mutants, highlights the key role of FBXO7-INF2-DRP1 axis in ECa tumorigenesis and provides a new viewpoint to treat ECa patients with FBXO7 deletion or mutations by targeting INF2-DRP1 axis-associated mitochondrial division.

The roles of G3BP1 in human diseases (review).

Ras-GTPase-activating protein binding protein 1 (G3BP1) is a multifunctional binding protein involved in a variety of biological functions, including cell proliferation, metastasis, apoptosis, differentiation and RNA metabolism. It has been revealed that G3BP1, as an antiviral factor, can interact with viral proteins and regulate the assembly of stress granules (SGs), which can inhibit viral replication. Furthermore, several viruses have the ability to hijack G3BP1 as a cofactor, recruiting translation initiation factors to promote viral proliferation. However, many functions of G3BP1 are associated with other diseases. In various cancers, G3BP1 is a cancer-promoting factor, which can promote the proliferation, invasion and metastasis of cancer cells. Moreover, compared with normal tissues, G3BP1 expression is higher in tumor tissues, indicating that it can be used as an indicator for cancer diagnosis. In this review, the structure of G3BP1 and the regulation of G3BP1 in multiple dimensions are described. In addition, the effects and potential mechanisms of G3BP1 on various carcinomas, viral infections, nervous system diseases and cardiovascular diseases are elucidated, which may provide a direction for clinical applications of G3BP1 in the future.