Project description:Within the endolysosomal pathway in mammalian cells, ESCRT complexes facilitate degradation of membrane proteins from limiting membranes of late endosomes. Recent studies revealed that yeast ESCRT proteins also sort for degradation, ubiquitinated proteins from vacuolar membrane. However, whether mammalian ESCRTs perform similar function at lysosomes remained unknown. Here, we studied the involvement of mammalian ESCRT-I in maintaining lysosomal membrane homeostasis and its implication in lysosome-related signaling. We show that ESCRT-I restricts the size of lysosomes and promotes degradation of lysosomal Ca2+ channel, MCOLN1 protein. ESCRT-I depletion induced transcriptional response related to MiT-TFE signaling and cholesterol biosynthesis, pointing to lysosomal dysfunction. The lack of ESCRT-I promoted abnormal cholesterol accumulation on lysosomes and activated TFEB/TFE3 transcription factors in Ca2+-MCOLN1-dependent, but lipid-independent manner. Hence, our study provides evidence that ESCRT-I maintains lysosomal homeostasis and elucidates MiT-TFE regulatory mechanism activated in response to ESCRT-I deprivation
Project description:We report that CCF nucleus-to-cytoplasm shuttling in senescence is mediated by nuclear egress, mediated by ESCRT-III and Torsin complex. We inhibit ESCRT-III by KO ALIX, and Torsin by KO TOR1A.
Project description:The ESCRT machinery drives the multivesicular body (MVB) pathway in eukaryotic cells and thus is required for the degradation of ubiquitinated membrane proteins in lysosomes. To systematically characterize how cells respond to loss of ESCRT function, we used quantitative proteomics and gene expression profiling in yeast. We find that ESCRT mutants display severe defects in amino acid homeostasis, resulting in lower levels of free intracellular amino acids. This deficit renders the growth of ESCRT mutants highly sensitive to nutrient limitation. Further proteomic analysis revealed that the MVB pathway essentially contributes to proteome remodeling under nutrient limitation. The rapid decline of protein synthesis upon starvation no longer enables ESCRT mutants to complete their cell cycle and properly enter a quiescent state, which strongly affects their long-term survival. Thus, the MVB pathway functions to selectively down-regulate integral membrane proteins and, together with autophagy and proteasomal degradation, considerably contributes to amino acid recycling. We used microarrays to identify gene expression changes between delta VPS4 knock out and wild type Saccharomyces cerevisiae strains
Project description:While liganded nuclear receptors are well established to regulate Pol II protein-coding transcription units, their role in regulation of DNA repeats remains largely unknown. Here, we report that ~2-3% of the ~1-200,000 human DR2 Alu repeats, particularly those in proximity to retinoic acid-activated Pol II transcription units, are bound and activated by retinoic acid receptor in human embryonic stem cells, triggering their Pol III-dependent transcription. The non-coding DR2 Alu transcripts are processed in a Dicer-dependent fashion into a series of small RNA products with sizes ranging ~28-65nt and exhibit substantial co-localization with P bodies. These small RNAs cause degradation of a subset of mRNAs critical for the "stem cell" state, which harbor complimentary sequences in their 3' untranslated regions. This regulation requires Ago3- dependent stabilization of full-length and processed DR2 Alu transcripts, and recruitment of Ago3-associated decapping complexes to the target mRNAs. Thus, the RAR/Pol III-dependent DR2 Alu transcriptional program in stem cells serves as a functional complement to the RAR/Pol II-dependent counterpart. ChIP-seq of H3K36me3 samples before and after RA (retinoic acid) treatments.
Project description:The proteasome is central to proteolysis by the ubiquitin-proteasome system under normal growth conditions but is itself degraded through macroautophagy under nutrient stress. A recently described AMPactivated protein kinase (AMPK)-regulated endosomal sorting complex required for transport (ESCRT)-dependent microautophagy pathway also regulates proteasome trafficking and degradation in low-glucose conditions in yeast. Aberrant proteasomes are more prone to microautophagy, suggesting the ESCRT system fine-tunes proteasome quality control under low-glucose stress. Here, we uncover additional features of the selective microautophagy of proteasomes in budding yeast. Genetic or pharmacological induction of aberrant proteasomes is associated with increased mono- or oligo-ubiquitylation of proteasome components, which appears to be recognized by ESCRT-0. AMPK controls this pathway in part by regulating the trafficking of ESCRT-0 to the vacuole surface, which also leads to degradation of the Vps27 subunit of ESCRT-0. The Rsp5 ubiquitin ligase contributes to proteasome subunit ubiquitylation, and multiple ubiquitin-binding elements in Vps27 are involved in their recognition.We propose that ESCRT-0 at the vacuole surface recognizes ubiquitylated proteasomes and initiates their microautophagic elimination during glucose depletion.
Project description:Fully grown oocytes remain transcriptionally quiescent, yet many maternal mRNAs are synthesized and retained in growing oocytes. We now know that maternal mRNAs are stored in a structure called the mitochondria associated ribonucleoprotein domain (MARDO). But the components and functions of MARDO remain elusive. Here, we found that LSM14B knockout prevents the proper storage and timely clearance of mRNAs (including Cyclin B1, Btg4, and other mRNAs that are translationally activated during meiotic maturation), specifically by disrupting MARDO assembly during oocyte growth and meiotic maturation. With decreased levels of storage and clearance, the LSM14B knockout oocytes failed to enter meiosis II, ultimately resulting in female infertility. Our results demonstrate the function of LSM14B in MARDO assembly, couple the MARDO with mRNA clearance and oocyte meiotic maturation
Project description:The activation of Mixed Lineage Kinase-Like (MLKL) by Receptor Interacting Protein Kinase-3 (RIPK3) results in plasma membrane (PM) disruption and a form of regulated necrosis, called necroptosis. Here we show that during necroptosis, MLKL-dependent calcium (Ca++) influx and phosphatidylserine (PS) exposure on the outer leaflet of the plasma membrane preceded loss of PM integrity. Activation of MLKL results in the generation of broken, PM “bubbles” with exposed PS that are released from the surface of the otherwise intact cell. Components of the ESCRT machinery are required for formation of these bubbles, and act to sustain survival of the cell when MLKL activation is limited or reversed. Under conditions of necroptotic cell death, ESCRT controls the duration of plasma membrane integrity. As a consequence of the action of ESCRT, cells undergoing necroptosis can express chemokines and other regulatory molecules, and promote antigenic cross-priming of CD8+ T cells.