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Open Access Publications from the University of California

Scholarly Works (4 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2021)

The biogenesis of mitochondria depends on sophisticated import machineries to correctlytarget and fold cytosolically synthesized mitochondrial proteins. The mitochondrial import and assembly (MIA) pathway is a redox relay system that is essential for protein import into the intermembrane space (IMS) of mitochondria. It is unique that protein oxidation is tightly coupled to protein translocation. Given that the intermembrane space is highly relevant to a broad spectrum of diseases including apoptosis and neurodegeneration, additional research is needed to understand the underlying mechanism and new roles of regulation by the redox relay system. We have identified a novel protein, Aim32 that is dually localized in matrix and IMS. Aim32 is a thioredoxin-like [2Fe-2S] ferredoxin protein and binds with Erv1. Deletion of Aim32 or mutation of conserved cysteine residues resulted in an increased accumulation of proteins with aberrant disulfide linkages. In addition, the steady-state level of assembled mitochondrial protein import complexes was decreased, and a subset of the complexes showed disassembly. Aim32 also bound to several mitochondrial proteins through disulfide linkages, suggesting a function in maintaining the redox status of proteins by potentially targeting cysteine residues. These studies suggest that Aim32 may be poised as a sensor or regulator in quality control in a broad range of mitochondrial proteins. In addition to the function of ALR/Erv1 in protein translocation, it plays critical roles in various cellular pathways. We found ALR/Erv1 has an unexpected pro-survival role in hPSCs. A small molecule inhibitor that is specific for ALR/Erv1 was applied to investigate the hPSCs apoptosis and differentiation, which has the potential in hPSCs therapeutics.

    Cover page: Characterizing the Mitochondrial Redox Relay System
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2017)
    Glucocorticoids promote lipolysis in white adipose tissue (WAT) to adapt to energy demands under stress, whereas superfluous lipolysis causes metabolic disorders, including dyslipidemia and hepatic steatosis. Glucocorticoid-induced lipolysis requires the phosphorylation of cytosolic hormone-sensitive lipase (HSL) and perilipin 1 (Plin1) in the lipid droplet by protein kinase A (PKA). We previously identified Pik3r1 (also called p85α) as a glucocorticoid receptor target gene. Here, we found that glucocorticoids increased HSL phosphorylation, but not Plin1 phosphorylation, in adipose tissue-specific Pik3r1-null (AKO) mice. Furthermore, in lipid droplets, the phosphorylation of HSL and Plin1 and the levels of catalytic and regulatory subunits of PKA were increased by glucocorticoids in wild-type mice. However, these effects were attenuated in AKO mice. In agreement with reduced WAT lipolysis, glucocorticoid- initiated hepatic steatosis and hypertriglyceridemia were improved in AKO mice. Our data demonstrated a novel role of Pik3r1 that was independent of the regulatory function of phosphoinositide 3-kinase in mediating the metabolic action of glucocorticoids. Thus, the inhibition of Pik3r1 in adipocytes could alleviate lipid disorders caused by excess glucocorticoid exposure.
      Cover page: Pik3r1 Is Required for Glucocorticoid-Induced Perilipin 1 Phosphorylation in Lipid Droplet for Adipocyte Lipolysis.
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2016)
      Glucocorticoids and FoxO3 exert similar metabolic effects in skeletal muscle. FoxO3 gene expression was increased by dexamethasone (Dex), a synthetic glucocorticoid, both in vitro and in vivo. In C2C12 myotubes the increased expression is due to, at least in part, the elevated rate of FoxO3 gene transcription. In the mouse FoxO3 gene, we identified three glucocorticoid receptor (GR) binding regions (GBRs): one being upstream of the transcription start site, -17kbGBR; and two in introns, +45kbGBR and +71kbGBR. Together, these three GBRs contain four 15-bp glucocorticoid response elements (GREs). Micrococcal nuclease (MNase) assay revealed that Dex treatment increased the sensitivity to MNase in the GRE of +45kbGBR and +71kbGBR upon 30- and 60-min Dex treatment, respectively. Conversely, Dex treatment did not affect the chromatin structure near the -17kbGBR, in which the GRE is located in the linker region. Dex treatment also increased histone H3 and/or H4 acetylation in genomic regions near all three GBRs. Moreover, using chromatin conformation capture (3C) assay, we showed that Dex treatment increased the interaction between the -17kbGBR and two genomic regions: one located around +500 bp and the other around +73 kb. Finally, the transcriptional coregulator p300 was recruited to all three GBRs upon Dex treatment. The reduction of p300 expression decreased FoxO3 gene expression and Dex-stimulated interaction between distinct genomic regions of FoxO3 gene identified by 3C. Overall, our results demonstrate that glucocorticoids activated FoxO3 gene transcription through multiple GREs by chromatin structural change and DNA looping.
        Cover page: Transcriptional regulation of FoxO3 gene by glucocorticoids in murine myotubes
        • Article
        • Peer Reviewed
        UCLA Previously Published Works (2021)
        Yeast is a facultative anaerobe and uses diverse electron acceptors to maintain redox-regulated import of cysteine-rich precursors via the mitochondrial intermembrane space assembly (MIA) pathway. With the growing diversity of substrates utilizing the MIA pathway, understanding the capacity of the intermembrane space (IMS) to handle different types of stress is crucial. We used MS to identify additional proteins that interacted with the sulfhydryl oxidase Erv1 of the MIA pathway. Altered inheritance of mitochondria 32 (Aim32), a thioredoxin-like [2Fe-2S] ferredoxin protein, was identified as an Erv1-binding protein. Detailed localization studies showed that Aim32 resided in both the mitochondrial matrix and IMS. Aim32 interacted with additional proteins including redox protein Osm1 and protein import components Tim17, Tim23, and Tim22. Deletion of Aim32 or mutation of conserved cysteine residues that coordinate the Fe-S center in Aim32 resulted in an increased accumulation of proteins with aberrant disulfide linkages. In addition, the steady-state level of assembled TIM22, TIM23, and Oxa1 protein import complexes was decreased. Aim32 also bound to several mitochondrial proteins under nonreducing conditions, suggesting a function in maintaining the redox status of proteins by potentially targeting cysteine residues that may be sensitive to oxidation. Finally, Aim32 was essential for growth in conditions of stress such as elevated temperature and hydroxyurea, and under anaerobic conditions. These studies suggest that the Fe-S protein Aim32 has a potential role in general redox homeostasis in the matrix and IMS. Thus, Aim32 may be poised as a sensor or regulator in quality control for a broad range of mitochondrial proteins.
          Cover page: Aim32 is a dual-localized 2Fe-2S mitochondrial protein that functions in redox quality control
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