Project description:Spinal microglia play a pivotal role in the development of neuropathic pain. Peripheral nerve injury induces changes in the transcriptional profile of microglia, including increased expression of components of translational machinery. Whether microglial protein synthesis is stimulated following nerve injury and has a functional role in mediating pain hypersensitivity is unknown. Here, we show that nascent protein synthesis is upregulated in spinal microglia following peripheral nerve injury. Stimulating mRNA translation in microglia, via selective ablation of the translational repressor, eukaryotic initiation factor 4E-binding protein 1 (4E-BP1), promoted the transition of microglia to a reactive state and induced mechanical hypersensitivity. Conversely, inhibiting microglial translation by expressing mutant 4E-BP1 in microglia attenuated their peripheral nerve injury-induced activation and alleviated neuropathic pain. Thus, the stimulation of 4E-BP1-dependent translation promotes microglia reactivity and mechanical hypersensitivity, whereas its inhibition alleviates neuropathic pain.
Project description:Activation of the mechanistic target of rapamycin complex 1 (mTORC1) contributes to the development of chronic pain. However, the specific mechanisms by which mTORC1 causes hypersensitivity remain elusive. The eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) is a key mTORC1 downstream effector that represses translation initiation. Here we show that nociceptor-specific deletion of 4E-BP1, mimicking activation of mTORC1-dependent translation, is sufficient to cause mechanical hypersensitivity.
Project description:Eukaryotic translation initiation factor 4E (eIF4E)–binding protein 1 (4E-BP1) inhibits cap-dependent translation in eukaryotes by competing with eIF4G for an interaction with eIF4E. Phos-phorylation at Ser-83 of 4E-BP1 occurs during mitosis through the activity of cyclin-dependent kinase 1 (CDK1)/cyclin B rather than through canonical mTOR kinase activity. Here, we investi-gated the interaction of eIF4E with 4E-BP1 or eIF4G during interphase and mitosis. We observed that 4E-BP1 and eIF4G bind eIF4E at similar levels during interphase and mitosis. The most highly phosphorylated mitotic 4E-BP1 isoform (δ) did not interact with eIF4E, whereas a distinct 4E-BP1 phospho-isoform, EB-γ—phosphorylated at Thr-70, Ser-83, and Ser-101—bound to eIF4E during mitosis. Two-dimensional gel electropho-retic analysis corroborated the identity of the phosphorylation marks on the eIF4E-bound 4E-BP1 isoforms and uncovered a population of phosphorylated 4E-BP1 molecules lacking Thr-37/Thr-46–priming phosphorylation. Moreover, proximity ligation assays for phospho–4E-BP1 and eIF4E revealed different in situ interactions during interphase and mitosis. The eIF4E:eIF4G interaction was not inhibited, but rather increased in mitotic cells, consistent with active translation initiation during mitosis. Phospho-defective substitution of 4E-BP1 at Ser-83 did not change global translation or individual mRNA translation profiles as measured by single-cell nascent protein synthesis and eIF4G RNA-immunoprecipitation sequencing. Mitotic 5’-terminal oligopyrimidine RNA translation was active and, unlike interphase translation, resistant to mTOR inhibition. Our findings reveal the phosphorylation profiles of 4E-BP1 isoforms and their interactions with eIF4E throughout the cell cycle and indicate that 4E-BP1 does not specifically inhibit translation initiation during mitosis.
Project description:Evidence has long suggested that epidermal growth factor receptor (EGFR) may play a prominent role in triple-negative breast cancer (TNBC) pathogenesis, but clinical trials of EGFR inhibitors have yielded disappointing results. Using a candidate drug screen, we discovered that inhibition of cyclin-dependent kinases 12 and 13 (CDK12/13) dramatically sensitizes diverse models of TNBC to EGFR blockade. This combination therapy drives cell death through the 4E-BP1-dependent suppression of the translation and translation-linked turnover of driver oncoproteins, including MYC. A genome-wide CRISPR/Cas9 screen identified the CCR4-NOT complex as a major determinant of sensitivity to the combination therapy whose loss renders 4E-BP1 unresponsive to drug-induced dephosphorylation, thereby rescuing MYC translational suppression and promoting MYC stability. The central roles of CCR4-NOT and 4E-BP1 in response to the combination therapy were further underscored by the observation of CNOT1 loss and rescue of 4E-BP1 phosphorylation in TNBC cells that naturally evolved therapy resistance. Thus, pharmacological inhibition of CDK12/13 reveals a long proposed EGFR dependence in TNBC that functions through the cooperative regulation of translation-coupled oncoprotein stability.
Project description:Cyclin-dependent kinases 13 (CDK13) has been suggested to phosphorylate RNA polymerase II and is involved in transcriptional activation. However, whether CDK13 catalyzes other protein substrates and how CDK13 contributes to tumorigenesis remain largely unclear. Herein, we identify key translation machinery components 4E-BP1 and eIF4B as novel CDK13 substrates. CDK13 directly phosphorylates 4E-BP1 at Thr46 and eIF4B at Ser422 such that genetic or pharmacological inhibition of CDK13 perturbs RNA translation. Polysome profiling analysis shows that MYC oncoprotein synthesis depends on the CDK13-regulated translation in colorectal cancer (CRC), and CDK13 is required for CRC cell proliferation. As mTORC1 has been shown to phosphorylate the 4E-BP1 and eIF4B, knockdown or inhibition of CDK13 in combination with mTORC1 inhibitor rapamycin further dephosphorylates 4E-BP1 and eIF4B and blocks protein synthesis. As a result, dual inhibition of CDK13 and mTORC1 accelerated CRC cell death and again MYC were significantly downregulated upon combination treatment. These findings demonstrate a pro-tumorigenic role of CDK13 in CRC and shed light on the role of CDK13 in protein synthesis by direct phosphorylation of translation initiation factors. Therefore, therapeutic targeting of CDK13 alone or in combination with rapamycin may pave a new way for CRC treatment.
Project description:Although the mTOR-4E-BP1 signaling pathway is implicated in aging and aging-related disorders, the role of 4E-BP1 in regulating human stem cell homeostasis remains largely unknown. Here, we report that the expression of 4E-BP1 decreases along with the senescence of human mesenchymal stem cells (hMSCs). Genetic inactivation of 4E-BP1 in hMSCs accelerates cellular senescence, compromises mitochondrial respiration and increases mitochondrial ROS production. Mechanistically, the absence of 4E-BP1 destabilizes proteins in mitochondrial respiration complexes, especially several key subunits of the complex III including UQCRC2. Ectopic expression of 4E-BP1 attenuates mitochondrial abnormalities and alleviates cellular senescence in 4E-BP1-deficient hMSCs as well as in physiologically aged hMSCs. These findings together demonstrate that 4E-BP1 functions as a geroprotector to alleviate human stem cell senescence and maintain mitochondrial homeostasis, particularly for the mitochondrial respiration complex III and provide a new potential target to counteract human stem cell senescence.
Project description:Using mRNA-seq and ChIP-seq in muscle tissue, we found that BCL6 controls a broad range of anabolic targets, directly suppressing eukaryotic translation initiation factor 4E-binding protein 1 (Eif4epb1) and myostatin (Mstn) while enhancing insulin-like growth factor 1 (Igf1) and androgen receptor (Ar). Consistent with these gene regulatory effects, skeletal muscle ablation of Bcl6 increased physical association of the translation initiation factor eIF4E with its inhibitor EIF4E-BP1 and ribosomal sequencing in vivo revealed reduced translation efficiency.
Project description:Discodermolide treatment of A549 results in senescence. We compared cells resistant to disco-induced senescence to those that are sensitive to senescence induction. We also examined the gene expression of resistant (AD32) cells overexpressing 4E-BP1, a protein known to restore sensitivity to discodermolide in these cells. Total RNA was collected from A549, A549 disco, AD32, and AD32 4E-BP1 cells and gene expression profiles were examined.
Project description:Activation of brown adipose tissue (BAT) thermogenesis increases energy expenditure and alleviates obesity. Epigenetic regulation has emerged as a key mechanism underlying BAT development and function. To study the epigenetic regulation of BAT thermogenesis, we surveyed the expression of epigenetic enzymes that catalyze histone modifications in developmental beige adipocytes and found a unique expression pattern of suppressor of variegation 4-20 homolog 2 (Drosophila) (Suv420h2), a histone methyltransferase that preferentially catalyzes the tri-methylation at histone H4 lysine 20 (H4K20me3), a hallmark of gene silencing. Here we discovered that Suv420h2 expression parallels that of UCP1 expression in brown and beige adipocytes and that SUV420H2 knockdown significantly reduces, whereas SUV420H2 overexpression significantly increases UCP1 levels in brown adipocytes. Suv420h2 knockout (H2KO mice exhibit impaired cold-induced thermogenesis and are prone to diet-induced obesity. In contrast, mice with specific overexpression of Suv420h2 in adipocytes display enhanced cold-induced thermogenesis and are resistant to diet-induced obesity. Further study showed that Suv420h2 catalyzes H4K20 trimethylation at eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) promoter, leading to down-regulated expression of 4E-BP1, a negative regulator of the translation initiation complex. This in turn up-regulates PGC1α protein levels, which is associated with increased expression of thermogenic program. We conclude that Suv420h2 is a key regulator of brown/beige adipocyte development and thermogenesis.