Project description:Cell-cell fusion is a frequent and essential event during development, and its dysregulation causes diseases ranging from infertility to muscle weakness. Fusing cells repeatedly need to remodel their plasma membrane by orchestrated formation and disassembly of cortical actin filaments, but how the dynamic reorganization of the actin cytoskeleton control is still poorly understood. Here, we identified a ubiquitin- dependent toggle switch that establishes reversible actin bundling during mammalian cell fusion. We found that EPS8-IRSp53 complexes stabilize cortical actin bundles at sites of cell contact, which in part pushes cells towards each other. Conversely, EPS8 monoubiquitylation by CUL3KCTD10 displaces EPS8-IRSp53 from membranes and counteracts actin bundling, a dual activity that allows apposed cells to progress with fusion. We conclude that cytoskeletal rearrangements during development are precisely controlled by ubiquitylation, raising the possibility to modulate the efficiency of cell-cell fusion for therapeutic benefit.
Project description:HBP1 is a sequence-specific transcription factor which acts as a tumor inhibitor. HBP1 exerts tumor-suppressive function through regulating the expression of many genes during cell metabolism and cell cycle process. Posttranslational modification of HBP1 is crucial for its function. In this study, we found that HBP1 was methylated at R378 by PRMT1, which decreased 16 HBP1 protein stability by promoting its ubiquitination and proteasome-mediated degradation. PRMT1-mediated methylation of HBP1 could alleviate the repressive effects of HBP1 on tumor metastasis and growth through regulation of GSN expression. GSN was identified as a novel target gene of HBP1. Methylation of HBP1 promoted actin cytoskeleton remodeling and tumor progression by downregulating GSN levels. The methylated HBP1-GSN axis was also associated with the clinical outcomes of cancer patients. Targeting methylated HBP1-GSN axis may provide a therapeutic strategy for cancer. Significance: This investigation elucidated the mechanism of how methylation of HBP1 at R378 inhibits its tumor-suppressive function and promotes actin cytoskeleton remodeling, thus providing the strategy for targeting HBP1 during cancer treatment.
Project description:We describe a new mutant allele of the ACTIN2 gene with enhanced actin dynamics, displaying a broad array of twisting and bending phenotypes that resemble BR-treated plants. Moreover, auxin transcriptional regulation is enhanced on the mutant background, supporting the idea that shaping actin filaments is sufficient to modulate BR-mediated auxin responsiveness. The actin cytoskeleton thus functions as a scaffold for integration of auxin and BR signaling pathways.
Project description:We describe a new mutant allele of the ACTIN2 gene with enhanced actin dynamics, displaying a broad array of twisting and bending phenotypes that resemble BR-treated plants. Moreover, auxin transcriptional regulation is enhanced on the mutant background, supporting the idea that shaping actin filaments is sufficient to modulate BR-mediated auxin responsiveness. The actin cytoskeleton thus functions as a scaffold for integration of auxin and BR signaling pathways. Three biological replicates were performed for each sample (wild-type and actin2-5) and hybridized to the the Affymetrix ATH1 GeneChips.
Project description:Transcription factors (TFs) engage in various cellular essential processes including differentiation, growth and migration. However, the master TF involved in distant metastasis of nasopharyngeal carcinoma (NPC) remains largely unclear. Here we show that KLF5 regulates actin remodeling to enhance NPC metastasis. We analyzed the msVIPER algorithm-generated transcriptional regulatory networks and identified KLF5 as a master TF of metastatic NPC linked to poor clinical outcomes. KLF5 regulates actin remodeling and lamellipodia formation to promote the metastasis of NPC cells in vitro and in vivo. Mechanistically, KLF5 preferentially occupies distal enhancer regions of ACTN4 to activate its transcription, whereby decoding the informative DNA sequences. ACTN4, extensively localized within actin cytoskeleton, facilitates dense and branched actin networks and lamellipodia formation at the cell leading edge, empowering cells to migrate faster. Collectively, our findings reveal that KLF5 controls robust transcription program of ACTN4 to modulate actin remodeling and augment cell motility which enhances NPC metastasis, and provide new potential biomarkers and therapeutic interventions for NPC.
Project description:Transcription factors (TFs) engage in various cellular essential processes including differentiation, growth and migration. However, the master TF involved in distant metastasis of nasopharyngeal carcinoma (NPC) remains largely unclear. Here we show that KLF5 regulates actin remodeling to enhance NPC metastasis. We analyzed the msVIPER algorithm-generated transcriptional regulatory networks and identified KLF5 as a master TF of metastatic NPC linked to poor clinical outcomes. KLF5 regulates actin remodeling and lamellipodia formation to promote the metastasis of NPC cells in vitro and in vivo. Mechanistically, KLF5 preferentially occupies distal enhancer regions of ACTN4 to activate its transcription, whereby decoding the informative DNA sequences. ACTN4, extensively localized within actin cytoskeleton, facilitates dense and branched actin networks and lamellipodia formation at the cell leading edge, empowering cells to migrate faster. Collectively, our findings reveal that KLF5 controls robust transcription program of ACTN4 to modulate actin remodeling and augment cell motility which enhances NPC metastasis, and provide new potential biomarkers and therapeutic interventions for NPC.
Project description:The actin cytoskeleton is a three-dimensional scaffold of proteins that is a regulatory, energy-consuming material with dynamic properties shaping the structure and function of the cell. The proper function of actin is required for many cellular pathways, including cell division, autophagy, chaperone function, endocytosis, and exocytosis (1–5). The breakdown of these cellular processes manifests during aging and exposure to stress, which is in part due to the breakdown of the actin cytoskeleton (5–9). However, the regulatory mechanisms involved in preservation of cytoskeletal form and function are not well understood. Here, we performed a multi-pronged, cross-organismal screen combining a whole-genome CRISPR-Cas9 screen in human fibroblasts with in vivo C. elegans synthetic lethality screening. We identified the bromodomain protein, BET-1, as a key regulator promoting actin health and longevity. Interestingly, overexpression of bet-1 preserves actin health at late age and promotes lifespan and healthspan in C. elegans. These beneficial effects are through preservation of actin, downstream of the function of BET-1 as a transcriptional regulator. Together, our discovery attributes assigns a key role of BET-1 in cytoskeletal health, highlighting regulatory cellular networks promoting cytoskeletal homeostasis.
Project description:The actin cytoskeleton is a three-dimensional scaffold of proteins that is a regulatory, energy-consuming material with dynamic properties shaping the structure and function of the cell. The proper function of actin is required for many cellular pathways, including cell division, autophagy, chaperone function, endocytosis, and exocytosis (1–5). The breakdown of these cellular processes manifests during aging and exposure to stress, which is in part due to the breakdown of the actin cytoskeleton (5–9). However, the regulatory mechanisms involved in preservation of cytoskeletal form and function are not well understood. Here, we performed a multi-pronged, cross-organismal screen combining a whole-genome CRISPR-Cas9 screen in human fibroblasts with in vivo C. elegans synthetic lethality screening. We identified the bromodomain protein, BET-1, as a key regulator promoting actin health and longevity. Interestingly, overexpression of bet-1 preserves actin health at late age and promotes lifespan and healthspan in C. elegans. These beneficial effects are through preservation of actin, downstream of the function of BET-1 as a transcriptional regulator. Together, our discovery attributes assigns a key role of BET-1 in cytoskeletal health, highlighting regulatory cellular networks promoting cytoskeletal homeostasis.
Project description:Methylation of HBP1 by PRMT1 inhibits its tumor-suppressive function through regulating 2 GSN-mediated actin cytoskeleton remodeling
Project description:Amplification of the Melanocortin-1 Receptor in Nephrotic Syndrome Renders a Good Target for Podocyte Cytoskeleton Stabilization During the last years, several reports have been presented of beneficial effects of ACTH in patients with nephrotic syndrome. Among the known ACTH receptors, the melanocortin-1 receptor (MC1R) has been suggested as the mediator of the ACTH renoprotective effect with the mechanism of action resulting in stabilization of the actin cytoskeleton in podocytes. To understand how melanocortin receptors are regulated in nephrotic syndrome and how they are involved in restoration of filtration barrier function, melanocortin receptor expression was evaluated in patients and in a rat model of nephrotic syndrome in combination with cell culture analysis. Phosphoproteomic mass spectrometry was applied and identified MC1R pathways confirmed using biochemical analysis. We found that glomerular MC1R expression was increased in nephrotic syndrome, both in humans and in a rat model. A MC1R agonist protected podocytes from protamine sulfate induced stress fiber loss with the top ranked phoshoproteomic MC1R activated pathway beeing actin cytoskeleton signaling. Actin stabilization through the MC1R consisted of ERK1/2 dependent phosphorylation and inactivation of EGFR signaling with stabilization of synaptopodin and stress fibers in podocytes. These results further explain how patients with nephrotic syndrome show responsiveness to ACTH treatment by depressing EGFR signaling through activation of the MC1R receptor and as a consequence restore filtration barrier function by stabilizing the podocyte actin cytoskeleton.