Endosomal Deubiquitinating Enzymes Control Ubiquitination and Down-regulation of Protease-activated Receptor 2

The ␤-site amyloid precursor protein-cleaving enzyme (BACE1) is the rate-limiting enzyme in the production of amyloid-␤, the toxic peptide that accumulates in the brain of subjects affected by Alzheimer disease. Our previous studies have shown that BACE1 is degraded via the lysosomal pathway and that that depletion of the trafficking molecule Golgi-localized ␥-ear-containing ARF-binding protein 3 (GGA3) results in increased BACE1 levels and activity because of impaired lysosomal degradation. We also determined that GGA3 regulation of BACE1 levels requires its ability to bind ubiquitin. Accordingly, we reported that BACE1 is ubiquitinated at lysine 501 and that lack of ubiquitination at lysine 501 produces BACE1 stabilization. Ubiquitin conjugation is a reversible process mediated by deubiquitinating enzymes. The ubiquitin-specific peptidase 8 (USP8), an endosome-associated deubiquitinating enzyme, regulates the ubiquitination, trafficking, and lysosomal degradation of several plasma membrane proteins. Here, we report that RNAi-mediated depletion of USP8 reduced levels of both ectopically expressed and endogenous BACE1 in H4 human neuroglioma cells. Moreover, USP8 depletion increased BACE1 ubiquitination, promoted BACE1 accumulation in the early endosomes and late endosomes/lysosomes, and decreased levels of BACE1 in the recycling endosomes. We also found that decreased BACE1 protein levels were accompanied by a decrease in BACE1-mediated amyloid precursor protein cleavage and amyloid-␤ levels. Our findings demonstrate that USP8 plays a key role in the trafficking and degradation of BACE1 by deubiquitinating lysine 501. These studies suggest that therapies able to accelerate BACE1 degradation (e.g. by increasing BACE1 ubiquitination) may represent a potential treatment for Alzheimer disease.

Section: Usp8 Depletion Results In Bace1 Accumulation In Early Endososupporting

confidence: 93%

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

The Endosome-associated Deubiquitinating Enzyme USP8 Regulates BACE1 Enzyme Ubiquitination and Degradation

Yeates¹,

Tesco

2016

“…Endosome-Along with published evidence (19,22,23,37), the observations described above suggest that USP8 may function as a general regulator of Hrs-dependent trafficking at the sorting endosome. To investigate the cellular interactions between USP8 and the ESCRT-0 complex, BiFC microscopy was employed.…”

Section: Usp8 Modulates the Integrity Of The Endocytic Compartment Atmentioning

confidence: 52%

The Deubiquitinating Enzyme USP8 Promotes Trafficking and Degradation of the Chemokine Receptor 4 at the Sorting Endosome

Berlin¹,

Higginbotham

Dise

et al. 2010

Reversible ubiquitination orchestrated by the opposition of ubiquitin ligases and deubiquitinating enzymes mediates endocytic trafficking of cell surface receptors for lysosomal degradation. Ubiquitin-specific protease 8 (USP8) has previously been implicated in endocytosis of several receptors by virtue of their deubiquitination. The present study explores an indirect role for USP8 in cargo trafficking through its regulation of the chemokine receptor 4 (CXCR4). Contrary to the effects of USP8 loss on enhanced green fluorescent protein, we find that USP8 depletion stabilizes CXCR4 on the cell surface and attenuates receptor degradation without affecting its ubiquitination status. In the presence of ligand, diminished CXCR4 turnover is accompanied by receptor accumulation on enlarged early endosomes and leads to enhancement of phospho-ERK signaling. Perturbation in CXCR4 trafficking, resulting from USP8 inactivation, occurs at the ESCRT-0 checkpoint, and catalytic mutation of USP8 specifically targeted to the ESCRT-0 complex impairs the spatial and temporal organization of the sorting endosome. USP8 functionally opposes the ubiquitin ligase AIP4 with respect to ESCRT-0 ubiquitination, thereby promoting trafficking of CXCR4. Collectively, our findings demonstrate a functional cooperation between USP8, AIP4, and the ESCRT-0 machinery at the early sorting phase of CXCR4 and underscore the versatility of USP8 in shaping trafficking events at the earlyto-late endosome transition.Endocytosis and trafficking of cell surface receptors is essential for organized signal transduction and maintenance of homeostasis. Malfunctions along the molecular pathways governing endocytosis can lead to a wide range of human pathologies including metabolic disorders, autoimmune diseases, and cancer (1, 2). Ubiquitination, a reversible post-translational modification of proteins (3), mediates spatial and temporal aspects of endocytosis by dictating macromolecular complex assembly and cargo fate (4). Although polyubiquitination linked through Lys 48 of ubiquitin targets substrates for proteasomal degradation (5), mono-and Lys 63 -linked ubiquitination signal cargo trafficking (6), and modulate function of endocytic sorting machinery (7). The reversible nature of ubiquitination is imparted by deubiquitinating enzymes (DUBs) 4 and enables dynamic regulation of these ubiquitin-dependent processes in the cell (8).Trafficking of endocytosed cargo for degradation by the lysosome occurs in a series of discrete selection stages that utilize the endosomal sorting complexes required for transport (ESCRTs) -0, -I, -II, and -III. The ESCRT-0 complex, consisting of the adaptor proteins hepatocyte growth factor-regulated substrate (Hrs) and signal transducing adaptor molecule (STAM), resides at the sorting endosome and functions in the first step of cargo selection. ESCRT-0 partitions the endocytosed material arriving on the early endosomes between recycling and the multivesicular body (9 -11) and interacts with downstream ESCRT machinery (12, 13) respon...

“…The deubiquitinating enzyme, known as associated molecule with the SH3 domain of STAM (AMSH), has been implicated in the regulation of epidermal growth factor receptor, calcium-sensing receptor, and most recently, the ␦-opioid receptor and the protease-activated receptor 2 (37)(38)(39)(40)(41)(42)(43). AMSH was first identified as an interacting partner of the SH3 domain of STAM (44) and later characterized as a Zn 2ϩ -dependent ubiquitin isopeptidase with a substrate preference for Lys-63-linked polyubiquitin chains (37,45).…”

mentioning

confidence: 99%

AMSH Interacts with ESCRT-0 to Regulate the Stability and Trafficking of CXCR4

Sierra¹,

Wright

Nash

2010

Reversible ubiquitination is essential for the endocytic sorting and down-regulation of G protein-coupled receptors, such as the chemokine receptor CXCR4. The deubiquitinating enzyme AMSH has been implicated in the endocytic sorting of both G protein-coupled receptors and receptor-tyrosine kinases. Herein, we examine the role of AMSH in the regulation of CXCR4 stability and trafficking and characterize protein-protein interactions critical for this function. Loss of AMSH catalytic activity or depletion by RNAi results in increased steady-state levels of CXCR4 under basal conditions. Analysis of truncation and point mutation of AMSH reveal the importance of an RXXK motif for CXCR4 degradation. The RXXK motif of AMSH interacts with the SH3 domains of the STAM and Grb2 families of adaptor proteins with high affinity. Cells expressing a catalytically inactive mutant of AMSH show basal hyperubiquitination, but not increased degradation, of the ESCRT-0 components STAM1 and Hrs. This is dependent on the RXXK motif of AMSH. Ubiquitination of endocytic machinery modulates their activity, suggesting that AMSH may directly regulate endocytic adaptor protein function. This is reflected in CXCR4 trafficking and provides a mechanism by which AMSH specifies the fate of endocytosed receptors. Taken together, these studies implicate AMSH as a key modulator of receptor fate determination through its action on components of the endocytic machinery.The sorting and trafficking of cell surface receptors through endosomal compartments is a highly regulated process that is essential for maintaining cellular homeostasis and generating adaptive and coordinated responses to external stimuli. To avoid prolonged receptor activation and signaling, receptor-ligand complexes are endocytosed and either recycled back to the plasma membrane or sorted to lysosomes for degradation (1-4). This process is mediated by reversible ubiquitination. The modification of a target protein with ubiquitin moieties is extensively utilized to regulate the assembly of endosomal machinery as well as being a sorting signal for transmembrane proteins within the endosomal system (5-7). The crucial role for ubiquitination in the trafficking of endocytosed receptors has been documented for receptor-tyrosine kinases and a number of G protein-coupled receptors including the chemokine receptor CXCR4 (8 -10). CXCR4 has been extensively studied as a co-receptor for the entry of T-trophic human immunodeficiency virus into CD4ϩ T-cells (11,12). Along with its cognate ligand, Stromal cell-derived factor-1␣ (SDF-1/ CXCL12), CXCR4 plays important roles in hematopoiesis, development, and organization of the immune system and stem cell homing (13-15). CXCR4 deregulation is associated with various pathologies, including human immunodeficiency virus infection, cardiovascular disease, and neurodegenerative diseases and is associated with metastatic disease in a number of cancers (16 -20). Mutations that result in truncation of the C-terminal intracellular region of CXCR4 cause WHIM sy...