Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:6.3.2.19 (ubiquitin-protein ligase)
 799 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We recently reported the identification of a RING finger-containing protein, HHARI (human homologue of Drosophila ariadne), which binds to the human ubiquitin-conjugating enzyme UbcH7 in vitro. We now demonstrate that HHARI interacts and co-localizes with UbcH7 in mammalian cells, particularly in the perinuclear region. We have further defined a minimal interaction region of HHARI comprising residues 186-254, identified individual amino acid residues essential for the interaction, and determined that the distance between the RING1 finger and IBR (in between RING fingers) domains is critical to maintaining binding. We have also established that the RING1 finger of HHARI cannot be substituted for by the highly homologous RING finger domains of either of the ubiquitin-protein ligase components c-CBL or Parkin, despite their similarity in structure and their independent capabilities to bind UbcH7. Furthermore, mutation of the RING1 finger domain of HHARI from a RING-HC to a RING-H2 type abolishes interaction with UbcH7. These studies demonstrate that very subtle changes to the domains that regulate recognition between highly conserved components of the ubiquitin pathway can dramatically affect their ability to interact.
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PMID:Features of the parkin/ariadne-like ubiquitin ligase, HHARI, that regulate its interaction with the ubiquitin-conjugating enzyme, Ubch7. 1127 16

Association between protein inclusions and neurodegenerative diseases, including Parkinson's and Alzheimer's diseases, and polyglutamine disorders, has been widely documented. Although ubiquitin is conjugated to many of these aggregated proteins, the 26S proteasome does not efficiently degrade them. Mutations in the ubiquitin-protein ligase Parkin are associated with autosomal recessive juvenile Parkinsonism. Although Parkin-positive inclusions are not detected in brains of autosomal recessive juvenile Parkinsonism patients, Parkin is found in Lewy bodies in sporadic disease. This suggests that loss of Parkin ligase activity via mutation, or sequestration to Lewy bodies, is a contributory factor to sporadic disease onset. We now demonstrate that decreased proteasomal activity causes formation of large, noncytotoxic inclusions within the cytoplasm of both neuronal and nonneuronal cells overexpressing Parkin. This is not a general phenomenon as there is an absence of similar inclusions when HHARI, a structural homolog of Parkin, is overexpressed. The inclusions colocalize with ubiquitin and with proteasomes. Furthermore, Parkin inclusions colocalize with gamma-tubulin, acetylated alpha-tubulin, and cause redistribution of vimentin, suggesting aggresome-like properties. Our data imply that lower proteasomal activity, previously observed in brain tissue of Parkinson's disease patients, leads to Parkin accumulation and a concomitant reduction in ligase activity, thereby promoting Lewy body formation.
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PMID:Inhibition of proteasomal activity causes inclusion formation in neuronal and non-neuronal cells overexpressing Parkin. 1293 72

HHARI (also known as ARIH1) is an ubiquitin-protein ligase and is the cognate of the E2, UbcH7 (UBE2L3). To establish a functional role for HHARI in cellular proliferation processes, we performed a reverse genetics screen that identified n=86/522 (16.5%) ubiquitin conjugation components that have a statistically significant effect on cell proliferation, which included HHARI as a strong hit. We then produced and validated a panel of specific antibodies that establish HHARI as both a nuclear and cytoplasmic protein that is expressed in all cell types studied. HHARI was expressed at higher levels in nuclei, and co-localized with nuclear bodies including Cajal bodies (p80 coilin, NOPP140), PML and SC35 bodies. We confirmed reduced cellular proliferation after ARIH1 knockdown with individual siRNA duplexes, in addition to significantly increased levels of apoptosis, an increased proportion of cells in G2 phase of the cell cycle, and significant reductions in total cellular RNA levels. In head and neck squamous cell carcinoma biopsies, there are higher levels of HHARI expression associated with increased levels of proliferation, compared to healthy control tissues. We demonstrate that HHARI is associated with cellular proliferation, which may be mediated through its interaction with UbcH7 and modification of proteins in nuclear bodies.
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PMID:Human Homolog of Drosophila Ariadne (HHARI) is a marker of cellular proliferation associated with nuclear bodies. 2305 69