Project description:Auxin critically regulates nearly every aspect of plant growth and development. Auxin-driven transcriptional responses are mediated through the AUXIN RESPONSE FACTOR (ARF) family of transcription factors. Although ARF protein stability is regulated via the 26S proteasome, molecular mechanisms underlying ARF stability and turnover are unknown. Here, we report the identification and functional characterization of an F-Box E3 ubiquitin ligase, which we have named AUXIN RESPONSE FACTOR F-BOX1 (AFF1). AFF1 directly interacts with ARF19 and regulates its accumulation. Mutants defective in AFF1 display ARF19 protein hyperaccumulation, mild auxin resistance, and developmental defects. Together, our data suggest a new mechanism, namely control of ARF protein stability, in regulating auxin responsiveness.
Project description:Hematopoietic stem cell (HSC) differentiation is regulated by cell-intrinsic and extrinsic cues. In addition to transcriptional regulation, post-translational regulation may also control HSC differentiation. To test this hypothesis, we visualized ubiquitin-regulated protein stability of a single transcription factor, c-Myc. The stability of c-Myc protein was instructive of HSC quiescence and c-Myc protein abundance was controlled by the ubiquitin ligase Fbw7. Fine changes in stability of c-Myc protein regulated the HSC “gene expression signature”. Using whole genome genomic approaches, we identified specific regulators of HSC function that are directly controlled by c-Myc binding, however adult HSCs and embryonic stem cells sense and interpret distinctly c-Myc regulated gene expression. These studies show a ubiquitin ligase–substrate pair can orchestrate the molecular program of HSC differentiation.
Project description:E3 ubiquitin-ligases are important for the cellular protein homeostasis and their deregulation is implicated in cancer. The E3 ubiquitin-ligase Hakai is involved in tumour progression and metastasis, through the regulation of the tumour suppressor E-cadherin. Hakai is overexpressed in colon cancer, however, the implication in colitis-associated cancer is unknown. Here, we investigated the potential role of Hakai in intestinal inflammation and cancer bowel disease.Several mouse models of colitis and associated cancer were used including AOM-DSS, acute colitis, and genetically modified mice deficient for the IL-10 gene, to analyse Hakai expression by immunohistochemistry. Interactome analysis of Hakai was performed and effect on selected protein was determined by plasmid and siRNA transfection, western-blotting, immunoprecipitation, immunofluorescence and ubiquitination assays. Lipid accumulation was assayed by oil red staining. Immunohistochemistry was also performed in inflamed colon biopsies from ulcerative colitis, Crohn's disease and colorectal cancer patients. Our results show that Hakai was downregulated in inflammatory tissues in different mouse models. Fatty Acid Synthase (FASN) protein was identified as a novel Hakai-interacting protein. Hakai induces FASN ubiquitination and degradation via lysosome, thus regulating FASN-mediated lipid accumulation. An inverse expression of FASN with Hakai expression was detected in inflammatory AOM/DSS mouse model. In conclusion, Hakai regulates FASN ubiquitination and degradation, resulting in the regulation of FASN-mediated lipid accumulation, which is associated to the development of inflammatory bowel disease. The interaction between Hakai and FASN may be an important mechanism for the homeostasis of intestinal barrier function and in the pathogenesis of this disease.
Project description:The m6A modification regulates mRNA stability and translation. Here we show that transcriptomic m6A modification is dynamic and the m6A reader protein YTHDF2 promotes mRNA decay during the cell cycle. Depletion of YTHDF2 leads to the delay of mitotic entry due to overaccumulation of WEE1, a negative regulator of CDK1. We demonstrate that WEE1 transcripts contain m6A modification, which promotes their decay through the m6A reader YTHDF2. Moreover, we found that YTHDF2 protein stability is dependent on CDK1 activity. Thus, CDK1, YTHDF2, and WEE1 form a feedforward regulatory loop to promote mitotic entry. We further identified CUL1, CUL4A, DDB1, and SKP2 as components of E3 ubiquitin ligase complexes that mediate YTHDF2 proteolysis. Our study provides insights into how cell cycle mediators modulate transcriptomic m6A modification, which in turn regulates the cell cycle.
Project description:Hematopoietic stem cell (HSC) differentiation is regulated by cell-intrinsic and extrinsic cues. In addition to transcriptional regulation, post-translational regulation may also control HSC differentiation. To test this hypothesis, we visualized ubiquitin-regulated protein stability of a single transcription factor, c-Myc. The stability of c-Myc protein was instructive of HSC quiescence and c-Myc protein abundance was controlled by the ubiquitin ligase Fbw7. Fine changes in stability of c-Myc protein regulated the HSC âgene expression signatureâ. Using whole genome genomic approaches, we identified specific regulators of HSC function that are directly controlled by c-Myc binding, however adult HSCs and embryonic stem cells sense and interpret distinctly c-Myc regulated gene expression. These studies show a ubiquitin ligaseâsubstrate pair can orchestrate the molecular program of HSC differentiation. Gene expression profiles from c-Myc-High and c-Myc-Low expressing Lineage negative, c-Kit and Sca1 positive (LSKs) were compared using genome wide mRNA expression profiling by Affymetrix genechip arrays (Mouse 430 2.0) and key targets were validated by chromatin immunoprecipitation experiments.
Project description:The ubiquitin ligase Huwe1 regulates stem cell quiescence, maintenance and lymphoid specification by controlling the expression of N-Myc.