Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P50502 (Hip)
 7,003 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To maintain quality control in cells, mechanisms distinguish among improperly folded peptides, mature and functional proteins, and proteins to be targeted for degradation. The molecular chaperones, including heat-shock protein Hsp90, have the ability to recognize misfolded proteins and assist in their conversion to a functional conformation. Disruption of Hsp90 heterocomplexes by the Hsp90 inhibitor geldanamycin leads to substrate degradation through the ubiquitin-proteasome pathway, implicating this system in protein triage decisions. We previously identified CHIP (carboxyl terminus of Hsc70-interacting protein) to be an interaction partner of Hsc70 (ref. 4). CHIP also interacts directly with a tetratricopeptide repeat acceptor site of Hsp90, incorporating into Hsp90 heterocomplexes and eliciting release of the regulatory cofactor p23. Here we show that CHIP abolishes the steroid-binding activity and transactivation potential of the glucocorticoid receptor, a well-characterized Hsp90 substrate, even though it has little effect on its synthesis. Instead, CHIP induces ubiquitylation of the glucocorticoid receptor and degradation through the proteasome. By remodelling Hsp90 heterocomplexes to favour substrate degradation, CHIP modulates protein triage decisions that regulate the balance between protein folding and degradation for chaperone substrates.
 ...
PMID:The co-chaperone CHIP regulates protein triage decisions mediated by heat-shock proteins. 1114 32

Proper folding of proteins (either newly synthesized or damaged in response to a stressful event) occurs in a highly regulated fashion. Cytosolic chaperones such as Hsc/Hsp70 are assisted by cofactors that modulate the folding machinery in a positive or negative manner. CHIP (carboxyl terminus of Hsc70-interacting protein) is such a cofactor that interacts with Hsc70 and, in general, attenuates its most well characterized functions. In addition, CHIP accelerates ubiquitin-dependent degradation of chaperone substrates. Using an in vitro ubiquitylation assay with recombinant proteins, we demonstrate that CHIP possesses intrinsic E3 ubiquitin ligase activity and promotes ubiquitylation. This activity is dependent on the carboxyl-terminal U-box. CHIP interacts functionally and physically with the stress-responsive ubiquitin-conjugating enzyme family UBCH5. Surprisingly, a major target of the ubiquitin ligase activity of CHIP is Hsc70 itself. CHIP ubiquitylates Hsc70, primarily with short, noncanonical multiubiquitin chains but has no appreciable effect on steady-state levels or half-life of this protein. This effect may have heretofore unanticipated consequences with regard to the chaperoning activities of Hsc70 or its ability to deliver substrates to the proteasome. These studies demonstrate that CHIP is a bona fide ubiquitin ligase and indicate that U-box-containing proteins may comprise a new family of E3s.
 ...
PMID:CHIP is a U-box-dependent E3 ubiquitin ligase: identification of Hsc70 as a target for ubiquitylation. 1155 50

The ubiquitin-proteasome system catalyses the immediate destruction of misfolded or impaired proteins generated in cells, but how this proteolytic machinery recognizes abnormality of cellular proteins for selective elimination remains elusive. Here, we report that the C-terminus of Hsc70-interacting protein (CHIP) with a U-box domain is an E3 ubiquitin-ligase collaborating with molecular chaperones Hsp90 and Hsc70. Thermally denatured firefly luciferase was multiubiquitylated by CHIP in the presence of E1 and E2 (Ubc4 or UbcH5c) in vitro, only when the unfolded substrate was captured by Hsp90 or Hsc70 and Hsp40. No ubiquitylating activity was detected in CHIP lacking the U-box region. CHIP efficiently ubiquitylated denatured luciferase trapped by the C-terminal region of Hsp90, which contains a CHIP binding site. CHIP also showed self-ubiquitylating activity independent of target ubiquitylation. Our results indicate that CHIP can be regarded as 'a quality-control E3' that selectively ubiquitylates unfolded protein(s) by collaborating with molecular chaperones.
 ...
PMID:CHIP is a chaperone-dependent E3 ligase that ubiquitylates unfolded protein. 1174 28

BAG-1 is a ubiquitin domain protein that links the molecular chaperones Hsc70 and Hsp70 to the proteasome. During proteasomal sorting BAG-1 can cooperate with another co-chaperone, the carboxyl terminus of Hsc70-interacting protein CHIP. CHIP was recently identified as a Hsp70- and Hsp90-associated ubiquitin ligase that labels chaperone-presented proteins with the degradation marker ubiquitin. Here we show that BAG-1 itself is a substrate of the CHIP ubiquitin ligase in vitro and in vivo. CHIP mediates attachment of ubiquitin moieties to BAG-1 in conjunction with ubiquitin-conjugating enzymes of the Ubc4/5 family. Ubiquitylation of BAG-1 is strongly stimulated when a ternary Hsp70.BAG-1.CHIP complex is formed. Complex formation results in the attachment of an atypical polyubiquitin chain to BAG-1, in which the individual ubiquitin moieties are linked through lysine 11. The noncanonical polyubiquitin chain does not induce the degradation of BAG-1, but it stimulates a degradation-independent association of the co-chaperone with the proteasome. Remarkably, this stimulating activity depends on the simultaneous presentation of the integrated ubiquitin-like domain of BAG-1. Our data thus reveal a cooperative recognition of sorting signals at the proteolytic complex. Attachment of polyubiquitin chains to delivery factors may represent a novel mechanism to regulate protein sorting to the proteasome.
 ...
PMID:Ubiquitylation of BAG-1 suggests a novel regulatory mechanism during the sorting of chaperone substrates to the proteasome. 1229 98

The ubiquitin/proteasome system has been proposed to play an important role in Alzheimer's disease (AD) pathogenesis. However, the critical factor(s) modulating both amyloid-beta peptide (Abeta) neurotoxicity and ubiquitin/proteasome system in AD are not known. We report the isolation of an unusual ubiquitin-conjugating enzyme, E2-25K/Hip-2, as a mediator of Abeta toxicity. The expression of E2-25K/Hip-2 was upregulated in the neurons exposed to Abeta(1-42) in vivo and in culture. Enzymatic activity of E2-25K/Hip-2 was required for both Abeta(1-42) neurotoxicity and inhibition of proteasome activity. E2-25K/Hip-2 functioned upstream of apoptosis signal-regulating kinase 1 (ASK1) and c-Jun N-terminal kinase (JNK) in Abeta(1-42) toxicity. Further, the ubiquitin mutant, UBB+1, a potent inhibitor of the proteasome which is found in Alzheimer's brains, was colocalized and functionally interacted with E2-25K/Hip-2 in mediating neurotoxicity. These results suggest that E2-25K/Hip-2 is a crucial factor in regulating Abeta neurotoxicity and could play a role in the pathogenesis of Alzheimer's disease.
 ...
PMID:Essential role of E2-25K/Hip-2 in mediating amyloid-beta neurotoxicity. 1452 3

Kennedy's disease is a degenerative disorder of motor neurons caused by the expansion of a glutamine tract near the amino terminus of the androgen receptor (AR). Ligand binding to the receptor is associated with several post-translational modifications, but it is poorly understood whether these affect the toxicity of the mutant protein. Our studies now demonstrate that mutation of lysine residues in wild-type AR that are normally acetylated in a ligand-dependent manner mimics the effects of the expanded glutamine tract on receptor trafficking, misfolding, and aggregation. Mutation of lysines 630 or 632 and 633 to alanine markedly delays ligand-dependent nuclear translocation. The K632A/K633A mutant also undergoes ligand-dependent misfolding and aggregation similar to the expanded glutamine tract AR. This acetylation site mutant exhibits ligand-dependent 1C2 immunoreactivity, forms aggregates that co-localize with Hsp40, Hsp70, and the ubiquitin-protein isopeptide ligase (E3) ubiquitin ligase carboxyl terminus of Hsc70-interacting protein (CHIP), and inhibits proteasome function. Ligand-dependent nuclear translocation of the wild-type receptor and misfolding and aggregation of the K632A/K633A mutant are blocked by radicicol, an Hsp90 inhibitor. These data identify a novel role for the acetylation site as a regulator of androgen receptor subcellular distribution and folding and indicate that ligand-dependent aggregation is dependent upon intact Hsp90 function.
 ...
PMID:Androgen receptor acetylation site mutations cause trafficking defects, misfolding, and aggregation similar to expanded glutamine tracts. 1467 Sep 46

Here, we have used a chimera of green fluorescent protein (GFP) and the glucocorticoid receptor (GR) to study retrograde movement of a model soluble (i.e., non-vesicle-associated) protein in axons and dendrites of cultured NT2-N neurons. It is known that in non-neuronal cells, the GFP-GR moves from cytoplasm to the nucleus in a steroid-dependent manner by a rapid, hsp90-dependent mechanism. When rapid movement is inhibited by geldanamycin (GA), a specific inhibitor of the protein chaperone hsp90, the GFP-GR translocates slowly to the nucleus by diffusion. Here we show that GFP-GR expressed in hormone-free neurons is localized in both cytoplasm and neurites, and upon treatment with dexamethasone (DEX), it moves to the nucleus. In neurites, movement by diffusion is not possible, and we show that movement of the GFP-GR from neurites is blocked by geldanamycin, suggesting that the hsp90-dependent movement machinery is required for retrograde movement. In cells treated with both dexamethasone and geldanamycin, the GFP-GR becomes concentrated in fluorescent globules located periodically along the neurites. Carboxyl terminus of Hsc70-interacting protein (CHIP), the E3 ubiquitin ligase for the GR, also concentrates in the same loci in a steroid-dependent and geldanamycin-dependent manner. If geldanamycin is removed, the GFP-GR exits the globules and continues its retrograde movement. However, in the continued presence of geldanamycin, the GFP-GR in the globules undergoes proteasomal degradation, suggesting that the globules function as degradasomes. This is the first evidence for a linkage between receptor trafficking along neurites and receptor degradation by the proteasome.
 ...
PMID:Retrograde transport of the glucocorticoid receptor in neurites requires dynamic assembly of complexes with the protein chaperone hsp90 and is linked to the CHIP component of the machinery for proteasomal degradation. 1504 63

Although the ubiquitin-proteasome system and the molecular chaperones are implicated to play an important role in pathogenesis of familial amyotrophic lateral sclerosis (FALS) caused by mutations in Cu/Zn-superoxide dismutase (SOD1), the mechanism underlying the causes of this fatal disease is still poorly understood. Here we found that co-chaperone CHIP (carboxyl terminus of Hsc70-interacting protein), together with molecular chaperones Hsc70/Hsp70 and Hsp90, associates with FALS-linked mutant SOD1 proteins in cultured human cells. S5a subunit of 26S proteasomes, which recognizes polyubiquitylated proteins, also interacts with mutant SOD1 proteins. Over-expression of CHIP leads to the reduction in cellular levels of mutant SOD1 as well as the suppression of cytotoxicity induced by mutant SOD1. Unusually, rather than increasing the level of poly-ubiquitylated SOD1, over-expressed CHIP alters the ubiquitylation pattern of mutant SOD1 proteins. Both down-regulation and ubiquitylation of mutant SOD1 are greatly reduced by a mutant CHIP protein lacking U-box domain. Taken together, these results suggest that co-chaperone CHIP, possibly with another E3 ligase(s), modulates the ubiquitylation of mutant SOD1 and renders them more susceptible for proteasomal degradation.
 ...
PMID:Co-chaperone CHIP associates with mutant Cu/Zn-superoxide dismutase proteins linked to familial amyotrophic lateral sclerosis and promotes their degradation by proteasomes. 1535 45

Ubiquitin-positive deposits are histopathologically found in patients with Alzheimer's disease (AD). It is not understood why ubiquitin is accumulated in intra- and extra-cellular deposits or how it is involved in AD pathogenesis. Interestingly, recent evidence, including studies of E2-25K/Hip-2, has elucidated the molecular mechanism of the ubiquitin-proteasome system (UPS) malfunction in AD. The neurotoxicity and proteasome inhibition by Abeta, a main cause of AD pathogenesis, are mediated by increased E2-25K/Hip-2 in the brains of patients with AD. Furthermore, E2-25K/Hip-2 is required for the neurotoxicity that is mediated by a ubiquitin B mutant (UBB+1), which is a potent inhibitor of proteasomes that is found in patients with AD. Intensive research is required to identify the components of the UPS that are involved in AD pathogenesis.
 ...
PMID:Alzheimer's disease meets the ubiquitin-proteasome system. 1551 83

Recent evidence indicates that the transactivation of estrogen receptor alpha (ERalpha) requires estrogen-dependent receptor ubiquitination and degradation. Here we show that estrogen-unbound (unliganded) ERalpha is also ubiquitinated and degraded through a ubiquitin-proteasome pathway. To investigate this ubiquitin-proteasome pathway, we purified the ubiquitin ligase complex for unliganded ERalpha and identified a protein complex containing the carboxyl terminus of Hsc70-interacting protein (CHIP). CHIP preferentially bound to misfolded ERalpha and ubiquitinated it to induce degradation. Ligand binding to the receptor induced the dissociation of CHIP from ERalpha. In CHIP-/- cells, the degradation of unliganded ERalpha was abrogated; however, estrogen-induced degradation was observed to the same extent as in CHIP+/+ cells. Our findings suggest that ERalpha is regulated by two independent ubiquitin-proteasome pathways, which are switched by ligand binding to ERalpha. One pathway is necessary for the transactivation of the receptor and the other is involved in the quality control of the receptor.
 ...
PMID:Ligand-dependent switching of ubiquitin-proteasome pathways for estrogen receptor. 1553 84


1 2 3 4 Next >>