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Open Access Publications from the University of California

Scholarly Works (4 results)

  • Thesis
  • Peer Reviewed
UC San Francisco Electronic Theses and Dissertations (2011)

This thesis addresses the endosomal sorting of the beta-2 adrenergic receptor (B2AR), a "typical" (family A) member of the large superfamily of seven-transmembrane signaling receptors, the G-protein coupled receptors (GPCRs). The introductory chapter provides background on the general importance of sorting in the cell, how sorting affects signaling receptors, models for protein sorting, a primer on sequence based sorting, and a brief explanation of the scientific approach I took in my thesis work. The 2nd chapter details findings on the role of ubiquitin and the ESCRT machinery in sorting of B2AR. We find that direct receptor ubiquitination plays no role in endosomal sorting of B2AR to the lysosome. Chapter 3 explores the role of actin in maintaining a subset of endosomal tubules which are important for B2AR recycling. In chapter 4, a direct interactor of the B2AR sorting sequence, SNX27, is identified and its role in recycling of B2AR is chronicled. Chapter 5 introduces the retromer complex as the endosomal sorting location for B2AR. Further, it elucidates the connectivity of SNX27 to the retromer and demonstrates a role for SNX27 in receptor entry into the retromer tubule. Lastly, Chapter 6 explores the results presented in the previous chapters, attempts to reconcile them with the "big picture," and suggests avenues for future study.

    Cover page: Elucidating the Post-Endocytic Sorting Mechanism of the Beta-2 Adrenergic Receptor
    • Article
    • Peer Reviewed
    UC San Francisco Previously Published Works (2011)
    Endocytic sorting of signalling receptors between recycling and degradative pathways is a key cellular process controlling the surface complement of receptors and, accordingly, the cell's ability to respond to specific extracellular stimuli. The β2 adrenergic receptor (β2AR) is a prototypical seven-transmembrane signalling receptor that recycles rapidly and efficiently to the plasma membrane after ligand-induced endocytosis. β2AR recycling is dependent on the receptor's carboxy-terminal PDZ ligand and Rab4. This active sorting process is required for functional resensitization of β2AR-mediated signalling. Here we show that sequence-directed sorting occurs at the level of entry into retromer tubules and that retromer tubules are associated with Rab4. Furthermore, we show that sorting nexin 27 (SNX27) serves as an essential adaptor protein linking β2ARs to the retromer tubule. SNX27 does not seem to directly interact with the retromer core complex, but does interact with the retromer-associated Wiskott-Aldrich syndrome protein and SCAR homologue (WASH) complex. The present results identify a role for retromer in endocytic trafficking of signalling receptors, in regulating a receptor-linked signalling pathway, and in mediating direct endosome-to-plasma membrane traffic.
      Cover page: SNX27 mediates retromer tubule entry and endosome-to-plasma membrane trafficking of signalling receptors
      • Article
      • Peer Reviewed
      UC San Francisco Previously Published Works (2010)
      Postsynaptic density 95/discs large/zonus occludens-1 (PDZ) domain-interacting motifs, in addition to their well-established roles in protein scaffolding at the cell surface, are proposed to act as cis-acting determinants directing the molecular sorting of transmembrane cargo from endosomes to the plasma membrane. This hypothesis requires the existence of a specific trans-acting PDZ protein that mediates the proposed sorting operation in the endosome membrane. Here, we show that sorting nexin 27 (SNX27) is required for efficient PDZ-directed recycling of the beta(2)-adrenoreceptor (beta(2)AR) from early endosomes. SNX27 mediates this sorting function when expressed at endogenous levels, and its recycling activity requires both PDZ domain-dependent recognition of the beta(2)AR cytoplasmic tail and Phox homology (PX) domain-dependent association with the endosome membrane. These results identify a discrete role of SNX27 in PDZ-directed recycling of a physiologically important signaling receptor, and extend the concept of cargo-specific molecular sorting in the recycling pathway.
        Cover page: SNX27 mediates PDZ-directed sorting from endosomes to the plasma membrane
        • Article
        • Peer Reviewed
        UC San Francisco Previously Published Works (2014)
        A fundamental and still largely unresolved question is how neurons achieve rapid delivery of selected signaling receptors throughout the elaborate dendritic arbor. Here we show that this requires a conserved sorting machinery called retromer. Retromer-associated endosomes are distributed within dendrites in ∼2 μm intervals and supply frequent membrane fusion events into the dendritic shaft domain immediately adjacent to (<300 nm from) the donor endosome and typically without full endosome discharge. Retromer-associated endosomes contain β-adrenergic receptors as well as ionotropic glutamate receptors, and retromer knockdown reduces extrasynaptic insertion of adrenergic receptors as well as functional expression of AMPA and NMDA receptors at synapses. We propose that retromer supports a broadly distributed network of plasma membrane delivery to dendrites, organized in micron-scale axial territories to render essentially all regions of the postsynaptic surface within rapid diffusion distance of a local exocytic event.
          Cover page: Retromer Mediates a Discrete Route of Local Membrane Delivery to Dendrites
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