SPOP promotes CREB5 ubiquitination to inhibit MET signaling in liver cancer.

Liver cancer is ranked as the sixth most prevalent from of malignancy globally and stands as the third primary contributor to cancer-related mortality. Metastasis is the main reason for liver cancer treatment failure and patient deaths. Speckle-type POZ protein (SPOP) serves as a crucial substrate junction protein within the cullin-RING E3 ligase complex, acting as a significant tumor suppressor in liver cancer. Nevertheless, the precise molecular mechanism underlying the role of SPOP in liver cancer metastasis remain elusive. In the current study, we identified cAMP response element binding 5 (CREB5) as a novel SPOP substrate in liver cancer. SPOP facilitates non-degradative K63-polyubiquitination of CREB5 on K432 site, consequently hindering its capacity to activate receptor tyrosine kinase MET. Moreover, liver cancer-associated SPOP mutant S119N disrupts the SPOP-CREB5 interactions and impairs the ubiquitination of CREB5.This disruption ultimately leads to the activation of the MET signaling pathway and enhances metastatic properties of hepatoma cells both in vitro and in vivo. In conclusion, our findings highlight the functional significance of the SPOP-CREB5-MET axis in liver cancer metastasis.

High dietary fructose promotes hepatocellular carcinoma progression by enhancing O-GlcNAcylation via microbiota-derived acetate.

Emerging studies have addressed the tumor-promoting role of fructose in different cancers. The effects and pathological mechanisms of high dietary fructose on hepatocellular carcinoma (HCC) remain unclear. Here, we examined the effects of fructose supplementation on HCC progression in wild-type C57BL/6 mice using a spontaneous and chemically induced HCC mouse model. We show that elevated uridine diphospho-N-acetylglucosamine (UDP-GlcNAc) and O-GlcNAcylation levels induced by high dietary fructose contribute to HCC progression. Non-targeted metabolomics and stable isotope tracing revealed that under fructose treatment, microbiota-derived acetate upregulates glutamine and UDP-GlcNAc levels and enhances protein O-GlcNAcylation in HCC. Global profiling of O-GlcNAcylation revealed that hyper-O-GlcNAcylation of eukaryotic elongation factor 1A1 promotes cell proliferation and tumor growth. Targeting glutamate-ammonia ligase or O-linked N-acetylglucosamine transferase (OGT) remarkably impeded HCC progression in mice with high fructose intake. We propose that high dietary fructose promotes HCC progression through microbial acetate-induced hyper-O-GlcNAcylation.

O-GlcNAcylation of SPOP promotes carcinogenesis in hepatocellular carcinoma.

Aberrantly elevated O-GlcNAcylation level is commonly observed in human cancer patients, and has been proposed as a potential therapeutic target. Speckle-type POZ protein (SPOP), an important substrate adaptor of cullin3-RING ubiquitin ligase, plays a key role in the initiation and development of various cancers. However, the regulatory mechanisms governing SPOP and its function during hepatocellular carcinoma (HCC) progression remain unclear. Here, we show that, in HCC, SPOP is highly O-GlcNAcylated by O-GlcNAc transferase (OGT) at Ser96. In normal liver cells, the SPOP protein mainly localizes in the cytoplasm and mediates the ubiquitination of the oncoprotein neurite outgrowth inhibitor-B (Nogo-B) (also known as reticulon 4 B) by recognizing its N-terminal SPOP-binding consensus (SBC) motifs. However, O-GlcNAcylation of SPOP at Ser96 increases the nuclear positioning of SPOP in hepatoma cells, alleviating the ubiquitination of the Nogo-B protein, thereby promoting HCC progression in vitro and in vivo. In addition, ablation of O-GlcNAcylation by an S96A mutation increased the cytoplasmic localization of SPOP, thereby inhibiting the Nogo-B/c-FLIP cascade and HCC progression. Our findings reveal a novel post-translational modification of SPOP and identify a novel SPOP substrate, Nogo-B, in HCC. Intervention with the hyper O-GlcNAcylation of SPOP may provide a novel strategy for HCC treatment.