MARCH6 promotes Papillary Thyroid Cancer development by destabilizing DHX9

AURKB targets DHX9 to promote hepatocellular carcinoma progression via PI3K/AKT/mTOR pathway

Aurora kinase B (AURKB) is known to play a carcinogenic role in a variety of cancers, but its underlying mechanism in liver cancer is unknown. This study aimed to investigate the role of AURKB in hepatocellular carcinoma (HCC) and its underlying molecular mechanism. Bioinformatics analysis revealed that AURKB was significantly overexpressed in HCC tissues and cell lines, and its high expression was associated with a poorer prognosis in HCC patients. Furthermore, downregulation of AURKB inhibited HCC cell proliferation, migration, and invasion, induced apoptosis, and caused cell cycle arrest. Moreover, AURKB downregulation also inhibited lung metastasis of HCC. AURKB interacted with DExH-Box helicase 9 (DHX9) and targeted its expression in HCC cells. Rescue experiments further demonstrated that AURKB targeting DHX9 promoted HCC progression through the PI3K/AKT/mTOR pathway. Our results suggest that AURKB is significantly highly expressed in HCC and correlates with patient prognosis. Targeting DHX9 with AURKB promotes HCC progression via the PI3K/AKT/mTOR pathway.

Membrane-associated RING-CH 7 inhibits stem-like capacities of bladder cancer cells by interacting with nucleotide-binding oligomerization domain containing 1

BACKGROUND

Cancer stem-like capacities are major factors contributing to unfavorable prognosis. However, the associated molecular mechanisms underlying cancer stem-like cells (CSCs) maintain remain unclear. This study aimed to investigate the role of the ubiquitin E3 ligase membrane-associated RING-CH 7 (MARCH7) in bladder cancer cell CSCs.

METHODS

Male BALB/c nude mice aged 4-5 weeks were utilized to generate bladder xenograft model. The expression levels of MARCHs were checked in online databases and our collected bladder tumors by quantitative real-time PCR (q-PCR) and immunohistochemistry (IHC). Next, we evaluated the stem-like capacities of bladder cancer cells with knockdown or overexpression of MARCH7 by assessing their spheroid-forming ability and spheroid size. Additionally, we conducted proliferation, colony formation, and transwell assays to validate the effects of MARCH7 on bladder cancer CSCs. The detailed molecular mechanism of MARCH7/NOD1 was validated by immunoprecipitation, dual luciferase, and in vitro ubiquitination assays. Co-immunoprecipitation experiments revealed that nucleotide-binding oligomerization domain-containing 1 (NOD1) is a substrate of MARCH7.

RESULTS

We found that MARCH7 interacts with NOD1, leading to the ubiquitin-proteasome degradation of NOD1. Furthermore, our data suggest that NOD1 significantly enhances stem-like capacities such as proliferation and invasion abilities. The overexpressed MARCH7 counteracts the effects of NOD1 on bladder cancer CSCs in both in vivo and in vitro models.

CONCLUSION

Our findings indicate that MARCH7 functions as a tumor suppressor and inhibits the stem-like capacities of bladder tumor cells by promoting the ubiquitin-proteasome degradation of NOD1. Targeting the MARCH7/NOD1 pathway could be a promising therapeutic strategy for bladder cancer patients.

Doa10/MARCH6 architecture interconnects E3 ligase activity with lipid-binding transmembrane channel to regulate SQLE

Transmembrane E3 ligases play crucial roles in homeostasis. Much protein and organelle quality control, and metabolic regulation, are determined by ER-resident MARCH6 E3 ligases, including Doa10 in yeast. Here, we present Doa10/MARCH6 structural analysis by cryo-EM and AlphaFold predictions, and a structure-based mutagenesis campaign. The majority of Doa10/MARCH6 adopts a unique circular structure within the membrane. This channel is established by a lipid-binding scaffold, and gated by a flexible helical bundle. The ubiquitylation active site is positioned over the channel by connections between the cytosolic E3 ligase RING domain and the membrane-spanning scaffold and gate. Here, by assaying 95 MARCH6 variants for effects on stability of the well-characterized substrate SQLE, which regulates cholesterol levels, we reveal crucial roles of the gated channel and RING domain consistent with AlphaFold-models of substrate-engaged and ubiquitylation complexes. SQLE degradation further depends on connections between the channel and RING domain, and lipid binding sites, revealing how interconnected Doa10/MARCH6 elements could orchestrate metabolic signals, substrate binding, and E3 ligase activity.

DHX9 Strengthens Atherosclerosis Progression By Promoting Inflammation in Macrophages

Atherosclerosis (AS) is the main cause of cerebrovascular diseases, and macrophages play important roles in atherosclerosis. DExH-Box helicase 9 (DHX9), as a member of DExD/H-box RNA helicase superfamily II, is identified as an autoantigen in the sera of systemic lupus erythematosus patients to trigger inflammation. The aim of this study was to investigate whether DHX9 is involved in AS development, especially in macrophages-mediated-inflammatory responses. We find that DHX9 expression is significantly increased in oxLDL or interferon-γ-treated macrophages and peripheral blood mononuclear cells (PBMCs) from patients with coronary artery disease (CAD). Knockdown of DHX9 inhibits lipid uptake and pro-inflammatory factors expression in macrophages, and ameliorates TNF-α-mediated monocyte adhesion capacity. Furthermore, we find that oxLDL stimulation promotes DHX9 interaction with p65 in macrophages, and further enhances the transcriptional activity of DHX9-p65-RNA Polymerase II complex to produce inflammatory factors. Moreover, using ApoE -/- mice fed with western diet to establish AS model, we find that knockdown of DHX9 mediated by adeno-associated virus-Sh-DHX9 through tail vein injection evidently alleviates AS progression in vivo. Finally, we also find that knockdown of DHX9 inhibits p65 activation, inflammatory factors expression, and the transcriptional activity of p65-RNA Polymerase II complex in PBMCs from patients with CAD. Overall, these results indicate that DHX9 promotes AS progression by enhancing inflammation in macrophages, and suggest DHX9 as a potential target for developing therapeutic drug.

A pan-cancer analysis of the expression and molecular mechanism of DHX9 in human cancers

Finding new targets is necessary for understanding tumorigenesis and developing cancer therapeutics. DExH-box helicase 9 (DHX9) plays a central role in many cellular processes but its expression pattern and prognostic value in most types of cancer remain unclear. In this study, we extracted pan-cancer data from TCGA and GEO databases to explore the prognostic and immunological role of DHX9. The expression levels of DHX9 were then verified in tumor specimens by western blot and immunohistochemistry (IHC). The oncogenic roles of DHX9 in cancers were further verified by in vitro experiments. We first verified that DHX9 is highly expressed in most tumors but significantly decreased in kidney and thyroid cancers, and it is prominently correlated with the prognosis of patients with different tumors. The phosphorylation level of DHX9 was also increased in cancers. Enrichment analysis revealed that DHX9 was involved in Spliceosome, RNA transport and mRNA surveillance pathway. Furthermore, DHX9 expression exhibited strong correlations with immune cell infiltration, immune checkpoint genes, and tumor mutational burden (TMB)/microsatellite instability (MSI). In liver, lung, breast and renal cancer cells, the knockdown or depletion of DHX9 significantly affected the proliferation, metastasis and EMT process of cancer cells. In summary, this pan-cancer investigation provides a comprehensive understanding of the prognostic and immunological role of DHX9 in human cancers, and experiments indicated that DHX9 was a potential target for cancer treatment.

Cholesterol synthesis enzyme SC4MOL is fine-tuned by sterols and targeted for degradation by the E3 ligase MARCHF6

Cholesterol biosynthesis is a highly regulated pathway, with over 20 enzymes controlled at the transcriptional and post-translational level. Whilst some enzymes remain stable, increased sterol levels can trigger degradation of several synthesis enzymes via the ubiquitin-proteasome system. Of note, we previously identified four cholesterol synthesis enzymes as substrates for one E3 ubiquitin ligase, membrane-associated RING-CH-type finger 6 (MARCHF6). Whether MARCHF6 targets the cholesterol synthesis pathway at other points is unknown. In addition, the post-translational regulation of many cholesterol synthesis enzymes, including the C4-demethylation complex (sterol-C4-methyl oxidase-like, SC4MOL; NAD(P) dependent steroid dehydrogenase-like, NSDHL; hydroxysteroid 17-beta dehydrogenase, HSD17B7) is largely uncharacterized. Using cultured mammalian cell-lines (human-derived and Chinese Hamster Ovary cells), we show SC4MOL, the first acting enzyme of C4-demethylation, is a MARCHF6 substrate, and is rapidly turned over and sensitive to sterols. Sterol depletion stabilizes SC4MOL protein levels, whilst sterol excess downregulates both transcript and protein levels. Furthermore, we found SC4MOL depletion by siRNA results in a significant decrease in total cell cholesterol. Thus, our work indicates SC4MOL is the most regulated enzyme in the C4-demethylation complex. Our results further implicate MARCHF6 as a crucial post-translational regulator of cholesterol synthesis, with this E3 ubiquitin ligase controlling levels of at least five enzymes of the pathway.

Phosphorylation of UHRF2 affects malignant phenotypes of HCC and HBV replication by blocking DHX9 ubiquitylation

Hepatitis B virus (HBV) infection is one of main contributors to poor prognosis and rapid progression of hepatocellular cancer (HCC). We previously identified the important role of the phosphorylation of ubiquitin-like with PHD and ring finger domains (UHRF2) in HBV-associated HCC. In this study we identify upregulated UHRF2 protein levels in HBV-associated HCC cells and tissues. UHRF2 overexpression promotes the viability, proliferation, migration and invasiveness of HBV-positive HCC cell lines, and enhances HBV DNA replication. To obtain a comprehensive understanding of the interaction networks of UHRF2 and their underlying mechanism, this study suggests that UHRF2 facilitates the ubiquitin-proteasome-mediated proteolysis of DExD/H (Asp-Glu-Ala-His) -box helicase enzyme 9 (DHX9). However, phosphorylation of UHRF2 by HBx at S643 inhibits E3 ubiquitin ligase activity of UHRF2 and improves DHX9 protein stability. Furthermore, results suggest that HBx promotes phosphorylation of UHRF2 by the ETS1-CDK2 axis through the downregulation of miR-222-3p in HBV-associated HCC specimens and cells. Our findings suggest that HBx-induced phosphorylation of UHRF2 S643 acts as a "switch" in HBV-associated HCC oncogenesis, activating the positive feedback between phosphorylated UHRF2 and HBV, provide evidence that UHRF2 is a new regulator and a potential prognostic indicator of poor prognosis for HBV-associated HCC.

An NADPH sensor that regulates cell ferroptosis

Ferroptosis is a new form of programmed cell death, which achieved great breakthroughs in cell biology during past decade. However, the regulation of ferroptosis is yet to be identified thoroughly. The latest study published on Nature cell biology by Nguyen and colleagues found a new NADPH sensor, MARCHF6 an E3 ubiquitin ligase, mediates ferroptosis in tumor growth and animal development. This finding provides a novel insight into ubiquitin system and energy metabolism in regulation of ferroptosis, which may open up new avenues for tumor treatment.