Ubiquilin functions in autophagy and is degraded by chaperone-mediated autophagy.
Autophagy is the process by which organelles and portions of the cytoplasm are degraded in lysosomes. Several different forms of autophagy are known that are distinguishable chiefly by the mode in which cargo is delivered to the lysosome for degradation. Ubiquilin was recently reported to regulate macroautophagy, the form of autophagy in which cytosolic cargo is packaged in a double-membrane structure or autophagosome that fuses with lysosomes for degradation. We confirm here using different morphological and biochemical procedures that ubiquilin is present in autophagosomes in HeLa cells and in brain and liver tissue of mouse. Coimmunoprecipitation studies indicated that ubiquilin binds the autophagosome marker LC3 in a complex and that reduction of ubiquilin expression reduces autophagosome formation, which correlates with a reduction in maturation of LC3-I to the LC3-II form of the protein. We found that ubiquilin is degraded during both macroautophagy and during chaperone-mediated autophagy (CMA), the latter of which involves the active transport of proteins into lysosomes. We discuss the implication of this degradation in mediating cross-talk between macroautophagy and CMA. Finally, we demonstrate that ubiquilin protects cells against starvation-induced cell death propagated by overexpression of mutant Alzheimer's disease PS2N141I protein and green fluorescent protein (GFP)-huntingtin exon-1 fusion protein containing 74 polyglutamines.
Center for Biomedical Engineering and Technology, University of Maryland, Baltimore, 725 West Lombard Street, Baltimore, MD 21201, USA.
Cara
C
Rothenberg
Deepa
D
Srinivasan
Leann
L
Mah
Susmita
S
Kaushik
Corrine M
CM
Peterhoff
Janet
J
Ugolino
Shengyun
S
Fang
Ana Maria
AM
Cuervo
Ralph A
RA
Nixon
Mervyn J
MJ
Monteiro
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D001343:Autophagy; D000071183:Autophagy-Related Proteins; D015153:Blotting, Western; D001921:Brain / Q000378:metabolism / Q000648:ultrastructure; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D000071058:Huntingtin Protein; D008247:Lysosomes / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008856:Microscopy, Fluorescence; D016253:Microscopy, Immunoelectron; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D018832:Molecular Chaperones / Q000378:metabolism*; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D010455:Peptides / Q000235:genetics; D010588:Phagosomes / Q000378:metabolism; D053766:Presenilin-2 / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D034622:RNA Interference; D014162:Transfection; D018911:Trinucleotide Repeats / Q000235:genetics
D048868:Adaptor Proteins, Signal Transducing; D000071183:Autophagy-Related Proteins; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C086055:HTT protein, human; D000071058:Huntingtin Protein; C480860:Map1lc3b protein, mouse; D008869:Microtubule-Associated Proteins; D018832:Molecular Chaperones; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D010455:Peptides; D053766:Presenilin-2; C107792:UBQLN1 protein, human; D049452:Green Fluorescent Proteins; C097188:polyglutamine