Project description:Reprogramming gene expression at the translational level drives intestinal tumorigenesis. Codon decoding during translation elongation relies on tRNA modifications, while their pathological relevance in colorectal cancer remains to be elucidated. Here, we show that AlkB homolog 8 (ALKBH8), a uridine 34 (U34) tRNA methyltransferase, is a direct target of Wnt/β-catenin and is upregulated in colorectal cancer. Genetic ablation of ALKBH8 inhibits the development of intestinal tumors in Apcmin/+, AOM/DSS, and xenograft models. Loss of ALKBH8 induces ribosome pausing at adenine-ending codons, impairing the translation elongation of mRNAs enriched with these codons. Specifically, ALKBH8 regulates the translation of KRAS proto-oncogene in a codon-dependent manner. Rescue experiments demonstrate that the methyltransferase activity of ALKBH8 is required for its translation-promoting function. Together, our findings reveal ALKBH8-dependent mRNA translation as a critical mediator of intestinal tumorigenesis, underscoring its potential as a promising target for colorectal cancer therapy.
Project description:The Notch signaling pathway regulates fate decision, proliferation and differentiation of intestinal epithelial cells. However, the role of Notch signaling in colorectal cancer progression is largely unknown. Here we show that Notch signaling suppresses the progression of colorectal tumorigenesis, even though it augments tumor initiation. In contrast to adenomas of Apcmin mice, Notch-inactivated Apcmin adenomas showed more malignant characteristics, such as submucosal invasion and loss of glandular pattern. Conversely, Notch-activated Apcmin adenomas showed a reversion from high-grade to low-grade features, such as the restoration of adherent junctions. Expression profiling revealed that Notch signaling promotes the differentiation of tumor cells with down regulation of Wnt/beta-catenin target genes and inhibition of epithelial-mesenchymal transition. Comparison of mouse and human expression profiles also suggests the common role of Notch in inhibition of tumor progression. Interestingly, Notch signaling suppressed the expression of beta-catenin responsive genes through chromatin modification of Tcf4/beta-catenin binding sides. Our results suggest that Notch signaling has dual roles in colorectal tumorigenesis: promoting adenoma initiation, while inhibiting tumor progression to colorectal cancer. mRNAs from normal (WT, Notch-activated and Notch-inactivated) and tumor (WT, Notch-activated and Notch-inactivated) tissues were profiled.
Project description:Ribosome profiling data reports on the distribution of translating ribosomes, at steady-state, with codon-level resolution. We present a robust method to extract codon translation rates and protein synthesis rates from these data, and identify causal features associated with elongation and translation efficiency in physiological conditions in yeast. We show that neither elongation rate nor translational efficiency is improved by experimental manipulation of the abundance or body sequence of the rare AGG tRNA. Deletion of three of the four copies of the heavily used ACA tRNA shows a modest efficiency decrease that could be explained by other rate-reducing signals at gene start. This suggests that correlation between codon bias and efficiency arises as selection for codons to utilize translation machinery efficiently in highly translated genes. We also show a correlation between efficiency and RNA structure calculated both computationally and from recent structure probing data, as well as the Kozak initiation motif, which may comprise a mechanism to regulate initiation. We test whether tRNA abundance affects elongation or translation efficiency by changing the tRNA levels through deletion or over expression and measuring the ribosomal dwell time at each codon using a robust statistical method that accounts for flow conservation.
Project description:Codon usage bias is a universal feature of eukaryotic and prokaryotic genomes and has been proposed to regulate translation efficiency, accuracy and protein folding based on the assumption that codon usage affects translation dynamics. The role of codon usage in regulating translation, however, is not clear and has been challenged by recent ribosome profiling studies. Here we used a Neurospora cell-free translation system to directly monitor the velocity of mRNA translation. We demonstrated that the use of preferred codons enhances the rate of translation elongation, whereas non-optimal codons slow translation. In addition, codon usage regulates ribosome traffic on the mRNA. These conclusions were supported by ribosome profiling results in vitro and in vivo with substrate mRNAs manipulated to increase signal over background noise. We further show that codon usage plays an important role in regulating protein function by affecting co-translational protein folding. Together, these results resolve a long-standing fundamental question and demonstrate the importance of codon usage on protein folding.
Project description:Metabolic reprogramming is a typical feature of tumors, in which biological macromolecules and energy produced in abnormal metabolism meet the requirements of highly proliferative tumor cells and participate in multiple stages of tumor development. High mobility group A1 (HMGA1) is a structural transcription factor, which plays a carcinogenic role in regulating the transcription of oncogenes. Bioinformatics analysis showed that HMGA1 was overexpressed in human CRC. However, the mechanisms by which HMGA1 promotes the tumorigenesis of CRC remains unknown. Herein, we applied intestinal epithelium conditional knockout (Hmga1△IEC) and knock-in (Hmga1IEC-OE/+) mice of HMGA1 to induce CRC, and identified that HMGA1 promotes colorectal cancer growth by increasing lipid synthesis. Single-cell sequencing (scRNA seq) and immunohistochemical staining showed that HMGA1 was highly expressed in the epithelial cells of CRC. HMGA1 promoted the CRC cell proliferation and accelerated CRC development in HMGA1-knock-in (Hmga1IEC-OE/+) mice. Knockout of HMGA1 (Hmga1△IEC) in intestinal epithelial cells of mice reduced the lipid accumulation and inhibited the occurrence and development of CRC. We further characterized that HMGA1 upregulated the level of fatty acid synthase (FASN) through enhancing the transcriptional binding of sterol regulatory element-binding protein 1 (SREBP1) to the promoter of FASN, leading to an increase in lipid synthesis in intestinal epithelial cells. High fat diet (HFD) aggravated the malignant progression of CRC in Hmga1△IEC mice and reversed the inhibitory effect of HMGA1 depletion on CRC. Administration Orlistat (50 mg/kg), an inhibitor of FASN-mediated lipid synthesis, into Hmga1-knock-in (Hmga1IEC-OE/+) mice markedly reduced lipid accumulation in intestinal epithelial cells and decreased the tumorigenesis of CRC. Taken together, our data suggest that HMGA1 promotes the tumorigenesis of colorectal cancer by up-regulating FASN-mediated de novo fatty acid synthesis. Our findings provide strong evidence supporting therapeutic intervention of lipid accumulation for the prevention and treatment of CRC