Mitf is a Schwann cell sensor of axonal integrity that drives nerve repair

Cell Reports · 2023 · 18 citations

• Cell biology
• Biology
• Neuroscience

Schwann cells respond to acute axon damage by transiently transdifferentiating into specialized repair cells that restore sensorimotor function. However, the molecular systems controlling repair cell formation and function are not well defined, and consequently, it is unclear whether this form of cellular plasticity has a role in peripheral neuropathies. Here, we identify Mitf as a transcriptional sensor of axon damage under the control of Nrg-ErbB-PI3K-PI5K-mTorc2 signaling. Mitf regulates a core transcriptional program for generating functional repair Schwann cells following injury and during peripheral neuropathies caused by CMT4J and CMT4D. In the absence of Mitf, core genes for epithelial-to-mesenchymal transition, metabolism, and dedifferentiation are misexpressed, and nerve repair is disrupted. Our findings demonstrate that Schwann cells monitor axonal health using a phosphoinositide signaling system that controls Mitf nuclear localization, which is critical for activating cellular plasticity and counteracting neural disease.

Live Cell Imaging of Yeast Golgi Dynamics

Methods in molecular biology · 2022 · 1 citations

• Cell biology
• Chemistry
• Biology

Mitf is a Schwann Cell Sensor of Axonal Integrity that Drives Nerve Repair

bioRxiv (Cold Spring Harbor Laboratory) · 2022-09-27 · 1 citations

Summary Schwann cells respond to acute axon damage by transiently transdifferentiating into specialized repair cells that restore sensorimotor function. However, the molecular systems controlling repair cell formation and function are not well defined and consequently it is unclear whether this form of cellular plasticity has a role in peripheral neuropathies. Here we identify Mitf as a transcriptional sensor of axon damage under the control of Nrg-ErbB-PI3K-PI5K-mTorc2 signaling. Mitf regulates a core transcriptional program for generating functional repair Schwann cells following injury and during peripheral neuropathies caused by CMT4J and CMT4D. In the absence of Mitf , core genes for epithelial-to-mesenchymal transition, metabolism and dedifferentiation are misexpressed and nerve repair is disrupted. Taken together, our findings demonstrate that Schwann cells monitor axonal health using a phosphoinositide signaling system that controls Mitf, which is critical for activating cellular plasticity and counteracting neural disease. Highlights Mitf-induced Schwann cell plasticity is triggered by peripheral neuropathy. Nrg-ErbB signaling activates Mitf via cytoplasmic-to-nuclear translocation. Mitf restores sensorimotor function following axonal breakdown. Mitf regulates a core repair program across both injury and neurodegeneration.

Conserved role for Gga proteins in phosphatidylinositol 4-kinase localization to the <i>trans</i> -Golgi network

Proceedings of the National Academy of Sciences · 2017-03-13 · 36 citations

-Golgi network (TGN), phosphatidylinositol 4-phosphate (PtdIns4P) plays important roles in recruitment of two major clathrin adaptors, Gga (Golgi-localized, gamma-adaptin ear homology, Arf-binding) proteins and the AP-1 (assembly protein-1) complex. The molecular mechanisms that mediate localization of phosphatidylinositol kinases responsible for synthesis of PtdIns4P at the TGN are not well characterized. We identify two motifs in the yeast phosphatidylinositol 4-kinase, Pik1, which are required for binding to the VHS domain of Gga2. Mutations in these motifs that inhibit Gga2-VHS binding resulted in reduced Pik1 localization and delayed accumulation of PtdIns4P and recruitment of AP-1 to the TGN. The Pik1 homolog in mammals, PI4KIIIβ, interacted preferentially with the VHS domain of GGA2 compared with VHS domains of GGA1 and GGA3. Depletion of GGA2, but not GGA1 or GGA3, specifically affected PI4KIIIβ localization. These results reveal a conserved role for Gga proteins in regulating phosphatidylinositol 4-kinase function at the TGN.

Mechanisms of Phosphoinositide-Mediated Clathrin Adaptor Progression at the trans-Golgi Network

eScholarship (California Digital Library) · 2013-01-01

Clathrin-mediated trafficking is a conserved process during which clathrin coated vesicles transport cargo between the trans-Golgi Network (TGN) and the endosomes, and during the process of endocytosis. These studies identify a previously unrecognized sequence of assembly between adaptor-specific clathrin coated vesicles. At the TGN, we found that GGA-enriched vesicles form first, followed by the biogenesis of AP-1 enriched vesicles. We then identified the mechanism by which this process is temporally controlled. We have identified a novel direct physical interaction between the VHS domain of Gga2 and the yeast PI(4)-Kinase, Pik1p, that is important for the recruitment of Pik1p to the TGN membrane. Deletion of GGA proteins results in the delay of PI(4)P accumulation and Pik1p recruitment. Furthermore, we have mapped the regions through which Pik1p interacts with Gga2 and demonstrate that these binding sites are important for the Pik1p-GGA interaction in vivo. Disruption of these binding sites through mutation results in delayed PI(4)P accumulation, mislocalized Ent5p and delayed AP-1 recruitment. We also provide evidence that this Pik1/GGA interaction is regulated by GTP-Arf1. Arf1 binds to the GAT domain of GGA2, enabling Pik1p to directly bind to the VHS domain of Pik1p. We also find that this network of physical interactions is conserved in mammals.

Phosphoinositide-mediated clathrin adaptor progression at the trans-Golgi network

Nature Cell Biology · 2012-02-17 · 140 citations

Yeast Irc6p is a novel type of conserved clathrin coat accessory factor related to small G proteins

Molecular Biology of the Cell · 2012-09-20 · 12 citations

Clathrin coat accessory proteins play key roles in transport mediated by clathrin-coated vesicles. Yeast Irc6p and the related mammalian p34 are putative clathrin accessory proteins that interact with clathrin adaptor complexes. We present evidence that Irc6p functions in clathrin-mediated traffic between the trans-Golgi network and endosomes, linking clathrin adaptor complex AP-1 and the Rab GTPase Ypt31p. The crystal structure of the Irc6p N-terminal domain revealed a G-protein fold most related to small G proteins of the Rab and Arf families. However, Irc6p lacks G-protein signature motifs and high-affinity GTP binding. Also, mutant Irc6p lacking candidate GTP-binding residues retained function. Mammalian p34 rescued growth defects in irc6 cells, indicating functional conservation, and modeling predicted a similar N-terminal fold in p34. Irc6p and p34 also contain functionally conserved C-terminal regions. Irc6p/p34-related proteins with the same two-part architecture are encoded in genomes of species as diverse as plants and humans. Together these results define Irc6p/p34 as a novel type of conserved clathrin accessory protein and founding members of a new G protein-like family.

Genome-wide Analysis of AP-3–dependent Protein Transport in Yeast

Molecular Biology of the Cell · 2008-12-31 · 52 citations

The evolutionarily conserved adaptor protein-3 (AP-3) complex mediates cargo-selective transport to lysosomes and lysosome-related organelles. To identify proteins that function in AP-3-mediated transport, we performed a genome-wide screen in Saccharomyces cerevisiae for defects in the vacuolar maturation of alkaline phosphatase (ALP), a cargo of the AP-3 pathway. Forty-nine gene deletion strains were identified that accumulated precursor ALP, many with established defects in vacuolar protein transport. Maturation of a vacuolar membrane protein delivered via a separate, clathrin-dependent pathway, was affected in all strains except those with deletions of YCK3, encoding a vacuolar type I casein kinase; SVP26, encoding an endoplasmic reticulum (ER) export receptor for ALP; and AP-3 subunit genes. Subcellular fractionation and fluorescence microscopy revealed ALP transport defects in yck3Delta cells. Characterization of svp26Delta cells revealed a role for Svp26p in ER export of only a subset of type II membrane proteins. Finally, ALP maturation kinetics in vac8Delta and vac17Delta cells suggests that vacuole inheritance is important for rapid generation of proteolytically active vacuolar compartments in daughter cells. We propose that the cargo-selective nature of the AP-3 pathway in yeast is achieved by AP-3 and Yck3p functioning in concert with machinery shared by other vacuolar transport pathways.