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A postprandial increase of translation mediated by eukaryotic Initiation Factor 6 (eIF6) occurs in the liver. Its contribution to steatosis and disease is unknown. In this study we address whether eIF6-driven translation contributes to disease progression. eIF6 levels increase throughout the progression from Non-Alcoholic Fatty Liver Disease (NAFLD) to hepatocellular carcinoma. Reduction of eIF6 levels protects the liver from disease progression. eIF6 depletion blunts lipid accumulation, increases fatty acid oxidation (FAO) and reduces oncogenic transformation in vitro. In addition, eIF6 depletion delays the progression from NAFLD to hepatocellular carcinoma, in vivo. Mechanistically, eIF6 depletion reduces the translation of transcription factor C/EBPβ, leading to a drop in biomarkers associated with NAFLD progression to hepatocellular carcinoma and preserves mitochondrial respiration due to the maintenance of an alternative mTORC1-eIF4F translational branch that increases the expression of transcription factor YY1. We provide proof-of-concept that in vitro pharmacological inhibition of eIF6 activity recapitulates the protective effects of eIF6 depletion. We hypothesize the existence of a targetable, evolutionarily conserved translation circuit optimized for lipid accumulation and tumor progression. Lipid accumulation in the liver leads to nonalcoholic fatty liver disease (NAFLD) that is a risk factor for developing hepatocellular carcinoma (HCC). Here, the authors show that activation of the translation initiation factor eIF6 promotes lipid accumulation in the liver and targeting eIF6 in murine models reduces NAFLD and associated HCC.

Breast cancer consists of highly heterogeneous tumors, whose cell of origin and driver oncogenes are difficult to be uniquely defined. Here we report that MYC acts as tumor reprogramming factor in mammary epithelial cells by inducing an alternative epigenetic program, which triggers loss of cell identity and activation of oncogenic pathways. Overexpression of MYC induces transcriptional repression of lineage-specifying transcription factors, causing decommissioning of luminal-specific enhancers. MYC-driven dedifferentiation supports the onset of a stem cell-like state by inducing the activation of de novo enhancers, which drive the transcriptional activation of oncogenic pathways. Furthermore, we demonstrate that the MYC-driven epigenetic reprogramming favors the formation and maintenance of tumor-initiating cells endowed with metastatic capacity. This study supports the notion that MYC-driven tumor initiation relies on cell reprogramming, which is mediated by the activation of MYC-dependent oncogenic enhancers, thus establishing a therapeutic rational for treating basal-like breast cancers. Breast cancer tumors originating from mammary luminal epithelial cells are highly heterogeneous. Here, the authors show MYC-driven tumor initiation is reliant on cell reprogramming via an epigenetic program which leads to mammary luminal epithelial cells acquiring basal/stem cell-like properties.

We performed a systematic analysis of the translation rate of tumor-infiltrating lymphocytes (TILs) and the microenvironment inputs affecting it, both in humans and in mice. Measurement of puromycin incorporation, a proxy of protein synthesis, revealed an increase of translating CD4 + and CD8 + cells in tumors, compared to normal tissues. High translation levels are associated with phospho-S6 labeling downstream of mTORC1 activation, whereas low levels correlate with hypoxic areas, in agreement with data showing that T cell receptor stimulation and hypoxia act as translation stimulators and inhibitors, respectively. Additional analyses revealed the specific phenotype of translating TILs. CD8 + translating cells have enriched expression of IFN-γ and CD-39, and reduced SLAMF6, pointing to a cytotoxic phenotype. CD4 + translating cells are mostly regulatory T cells (Tregs) with enriched levels of CTLA-4 and Ki67, suggesting an expanding immunosuppressive phenotype. In conclusion, the majority of translationally active TILs is represented by cytotoxic CD8 + and suppressive CD4 + Tregs, implying that other subsets may be largely composed by inactive bystanders.

Vanishing White Matter Disease (VWMD) is a devastating, currently incurable neurodevelopmental disorder primarily affecting white matter. The prevailing view attributes VWMD to the activation of the canonical integrated stress response (c-ISR). However, recent studies have identified a novel, distinct pathway called the split ISR (s-ISR), though its activation has so far only been documented in mouse stem cells harboring a single eIF2B mutation, leaving uncertainty about whether it occurs in human cells, whether other mutations can trigger it, and what role it plays in the disease. Here, we used prime editing (PE) to engineer multiple eIF2B pathogenic mutations into HEK293T and induced pluripotent stem cells (iPSCs), generating human models. We demonstrated PE’s effectiveness and safety, marking the first successful application of PE for modeling VWMD. We found that all modeled mutations activate the s-ISR, indicating that this response is a common feature across VWMD mutations, and that it can be further amplified by stress-induced c-ISR and effectively suppressed by ISRIB. Mechanistically, we show that s-ISR hinders mutant iPSCs from achieving the high protein synthesis levels necessary for proper differentiation, expecially into astrocytes. This impairment disrupts their maturation process, directly linking s-ISR activation to the white matter abnormalities of VWMD.

Nonalcoholic fatty liver disease (NAFLD) is characterized by the accumulation of lipids in the liver. Given the high prevalence of NAFLD, its evolution to nonalcoholic steatohepatitis (NASH) and hepatocellular carcinoma (HCC) is of global concern. Therapies for managing NASH-driven HCC can benefit from targeting factors that play a continuous role in NAFLD evolution to HCC. Recent work has shown that postprandial liver translation exacerbates lipid accumulation through the activity of a translation factor, eukaryotic initiation factor 6 (eIF6). Here, we test the effect of eIF6 inhibition on the progression of HCC. Mice heterozygous for eIF6 express half the level of eIF6 compared to wt mice and are resistant to the formation of HCC nodules upon exposure to a high fat/high sugar diet combined with liver damage. Histology showed that nodules in eIF6 het mice were smaller with reduced proliferation compared to wt nodules. By using an in vitro model of human HCC, we confirm that eIF6 depletion reduces the growth of HCC spheroids. We also tested three pharmacological inhibitors of eIF6 activity—eIFsixty-1, eIFsixty-4, and eIFsixty-6—and all three reduced eIF6 binding to 60S ribosomes and limited the growth of HCC spheroids. Thus, inhibition of eIF6 activity is feasible and limits HCC formation.

FAM46C is a tumor suppressor initially identified in multiple myeloma (MM) but increasingly recognized for its role also in other cancers. Despite its significance, studies exploring the therapeutic potential of FAM46C in combination with targeted treatments remain limited. Sphingosine kinases (SphK1 and SphK2) are key regulators of sphingolipid signaling, a pathway essential for maintaining cell structure and function but frequently deregulated in tumors, making them promising targets for cancer therapy. Preliminary work from our laboratory showed that FAM46C expression synergizes with administration of SKI-I, a pan-inhibitor of sphingosine kinases. In this study, we focused specifically on SphK1, the sphingosine kinase predominantly implicated in cancer and investigated the combinatorial effect of forced FAM46C expression and treatment with PF-543, a selective SphK1 inhibitor. We found that FAM46C overexpression enhances, whereas its downregulation reduces, the cytotoxic efficacy of PF-543 in MM cell lines. Using an in vivo xenograft model, we further validated these findings, showing that FAM46C-expressing MM tumors are indeed sensitive to PF-543 while tumors harboring the D90G loss-of-function variant of FAM46C are not. Overall, our results uncover a novel synergistic interaction between FAM46C expression and SphK1 inhibition, highlighting a promising therapeutic strategy for MM treatment.

Eukaryotic ribosome biogenesis and translation are linked processes that limit the rate of cell growth. Although ribosome biogenesis and translation are mainly controlled by distinct factors, eukaryotic initiation factor 6 (eIF6) has been found to regulate both processes. eIF6 is a necessary protein with a unique anti‐association activity, which prevents the interaction of 40S ribosomal subunits with 60S subunits through its binding to 60S ribosomes. In the nucleolus, eIF6 is a component of the pre‐ribosomal particles and is required for the biogenesis of 60S subunits, whereas in the cytoplasm it mediates translation downstream from growth factors. The translational activity of eIF6 could be due to its anti‐association properties, which are regulated by post‐translational modifications; whether this anti‐association activity is required for the biogenesis and nuclear export of ribosomes is unknown. eIF6 is necessary for tissue‐specific growth and oncogene‐driven transformation, and could be a new rate‐limiting step for the initiation of translation.

eIF6: transmitter to the 60S ribosome Translation initiation is influenced by input from extracellular stimuli. While two eukaryotic initiation factors (eIFs) are known to transduce external signals to the small (40S) ribosomal subunit, it was not known whether an eIF served a similar function for the large (60S) ribosomal subunit. In this study, Gandin et al. show that eIF6 communicates extracellular signals to the 60S subunit. Cells from an eIF6 heterozygous mouse show normal ribosome assembly but reduced translation, delayed cell cycle progression, and impaired transformation. This work suggests that eIF6 acts an initiation factor, in vivo, and may control growth and tumorigenesis. Although two eukaryotic initiation factors (eIFs) are known to transmit signals to the small ribosomal subunit, it was unknown whether an eIF served a similar function for the large ribosomal subunit. This study shows that eIF6 communicates extracellular signals to the 60S subunit. Cells from an eIF6 heterozygous mouse show normal ribosome biogenesis but reduced translation, delayed cell cycle progression, and impaired transformation. Cell growth and proliferation require coordinated ribosomal biogenesis and translation. Eukaryotic initiation factors (eIFs) control translation at the rate-limiting step of initiation 1 , 2 . So far, only two eIFs connect extracellular stimuli to global translation rates 3 : eIF4E acts in the eIF4F complex and regulates binding of capped messenger RNA to 40S subunits, downstream of growth factors 4 , 5 , and eIF2 controls loading of the ternary complex on the 40S subunit and is inhibited on stress stimuli 6 , 7 . No eIFs have been found to link extracellular stimuli to the activity of the large 60S ribosomal subunit. eIF6 binds 60S ribosomes precluding ribosome joining in vitro 8 , 9 , 10 . However, studies in yeasts showed that eIF6 is required for ribosome biogenesis rather than translation 11 , 12 , 13 , 14 . Here we show that mammalian eIF6 is required for efficient initiation of translation, in vivo . eIF6 null embryos are lethal at preimplantation. Heterozygous mice have 50% reduction of eIF6 levels in all tissues, and show reduced mass of hepatic and adipose tissues due to a lower number of cells and to impaired G1/S cell cycle progression. eIF6 +/- cells retain sufficient nucleolar eIF6 and normal ribosome biogenesis. The liver of eIF6 +/- mice displays an increase of 80S in polysomal profiles, indicating a defect in initiation of translation. Consistently, isolated hepatocytes have impaired insulin-stimulated translation. Heterozygous mouse embryonic fibroblasts recapitulate the organism phenotype and have normal ribosome biogenesis, reduced insulin-stimulated translation, and delayed G1/S phase progression. Furthermore, eIF6 +/- cells are resistant to oncogene-induced transformation. Thus, eIF6 is the first eIF associated with the large 60S subunit that regulates translation in response to extracellular signals.

Insulin regulates glycaemia, lipogenesis and increases mRNA translation. Cells with reduced eukaryotic initiation factor 6 (eIF6) do not increase translation in response to insulin. The role of insulin-regulated translation is unknown. Here we show that reduction of insulin-regulated translation in mice heterozygous for eIF6 results in normal glycaemia, but less blood cholesterol and triglycerides. eIF6 controls fatty acid synthesis and glycolysis in a cell autonomous fashion. eIF6 acts by exerting translational control of adipogenic transcription factors like C/EBPβ, C/EBPδ and ATF4 that have G/C rich or uORF sequences in their 5′ UTR. The outcome of the translational activation by eIF6 is a reshaping of gene expression with increased levels of lipogenic and glycolytic enzymes. Finally, eIF6 levels modulate histone acetylation and amounts of rate-limiting fatty acid synthase (Fasn) mRNA. Since obesity, type 2 diabetes, and cancer require a Fasn-driven lipogenic state, we propose that eIF6 could be a therapeutic target for these diseases. Insulin enhances mRNA translation via the translation initiation factor eIF6. Here, Brina et al . show that insulin-mediated activation of eIF6 is associated with the selective translation of genes involved in glycolysis and lipid synthesis with characteristic G/C-rich and uORF sequences in their mRNA.

Ribosomopathies are a family of inherited disorders caused by mutations in genes necessary for ribosomal function. Shwachman-Diamond Bodian Syndrome (SDS) is an autosomal recessive disease caused, in most patients, by mutations of the SBDS gene. SBDS is a protein required for the maturation of 60S ribosomes. SDS patients present exocrine pancreatic insufficiency, neutropenia, chronic infections, and skeletal abnormalities. Later in life, patients are prone to myelodisplastic syndrome and acute myeloid leukemia (AML). It is unknown why patients develop AML and which cellular alterations are directly due to the loss of the SBDS protein. Here we derived mouse embryonic fibroblast lines from an SbdsR126T/R126T mouse model. After their immortalization, we reconstituted them by adding wild type Sbds. We then performed a comprehensive analysis of cellular functions including colony formation, translational and transcriptional RNA-seq, stress and drug sensitivity. We show that: 1. Mutant Sbds causes a reduction in cellular clonogenic capability and oncogene-induced transformation. 2. Mutant Sbds causes a marked increase in immature 60S subunits, limited impact on mRNA specific initiation of translation, but reduced global protein synthesis capability. 3. Chronic loss of SBDS activity leads to a rewiring of gene expression with reduced ribosomal capability, but increased lysosomal and catabolic activity. 4. Consistently with the gene signature, we found that SBDS loss causes a reduction in ATP and lactate levels, and increased susceptibility to DNA damage. Combining our data, we conclude that a cell-specific fragile phenotype occurs when SBDS protein drops below a threshold level, and propose a new interpretation of the disease.