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1: Traffic. 2008 Jul;9(7):1146-56. Epub 2008 Apr 18.
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TrkA receptor endolysosomal degradation is both ubiquitin and proteasome dependent.

Geetha T, Wooten MW.

Department of Biological Sciences, Program in Cellular and Molecular Biosciences, Auburn University, Auburn, AL 36849, USA.

Gaps in our knowledge exist regarding the degradation of the tropomyosin-regulated kinase A (TrkA) receptor after addition of neurotrophin, nerve growth factor (NGF). TrkA is rapidly and transiently ubiquitinated upon addition of NGF. Here, we demonstrate that the polyubiquitin tag plays a definitive role in receptor sorting. Treatment of PC12 cells with lactacystin prevented NGF-dependent deubiquitination and degradation of TrkA. However, treatment with methylamine, bafilomycin or leupeptin, did not prevent NGF-dependent deubiquitination but blocked the degradation of TrkA. Employing co-immunoprecipitation, biochemical fractionation and confocal microscopy, the kinetics of receptor trafficking post-internalization was observed to occur as a sequel from endosome/multivesicular body, proteasomes, culminating with degradation in the lysosomes. The trafficking of the polyubiquitin-deficient TrkA receptor mutant K485R was impaired and likewise failed to degrade revealing that the receptor escapes degradation. The interaction of TrkA with proteasomes was confirmed by purification and co-immunoprecipitation. We provide evidence that proteasomal deubiquitinating enzymes trim K63-ubiquitin chains from the TrkA receptor prior to its delivery to lysosomes for degradation. Taken together, our results reveal the existence of a novel proteasome-dependent step in receptor degradation.

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PMID: 18419753 [PubMed - indexed for MEDLINE]