Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P62988 (Ubiquitin)
 4,326 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In the present study we have addressed the issue of proteasome independent cytosolic protein degradation. Tripeptidyl peptidase II (TPPII) has been suggested to compensate for a reduced proteasome activity, partly based on evidence using the inhibitor Ala-Ala-Phe-chloromethylketone (AAF-cmk). Here we show that AAF-cmk induces the formation of polyubiquitin-containing accumulations in osteosarcoma and Burkitt's lymphoma cell lines. These accumulations meet many of the landmarks of the aggresomes that form after proteasome inhibition. Using a combination of experiments with chemical inhibitors and interference of gene expression, we show that TPPII inhibition is not responsible for these accumulations. Our evidence suggests that the relevant target(s) is/are in the ubiquitin-proteasome pathway, most likely upstream the proteasome. We obtained evidence supporting this model by inhibition of Hsp90, which also acts upstream the proteasome. Although our data suggest that Hsp90 is not a target of AAF-cmk, its inhibition resulted in accumulations similar to those obtained with AAF-cmk. Therefore, our results question the proposed role for TPPII as a prominent alternative to the proteasome in cellular proteolysis.
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PMID:Accumulation of polyubiquitylated proteins in response to Ala-Ala-Phe-chloromethylketone is independent of the inhibition of Tripeptidyl peptidase II. 2055 80

Extralysosomal proteolysis is a multistep process involving the Ubiquitin- Proteasome System (UPS) and supplementary peptidases. Tripeptidyl peptidase II (TPPII) is the most extensively characterized enzyme, supplementing and sometimes substituting for proteasomal functions. In response to proteasome inhibition, polyubiquitinated proteins acting as proteasome substrates aggregate with proteasomes and form aggresomes. Several proteasome inhibitors are used as anti-cancer drugs. Thus, in our study, we used a novel fluorescent-tagged proteasome inhibitor BSc2118 to induce aggresome formation in C26 murine colon adenocarcinoma cells. It allowed us to obtain effective, inhibitor-based, proteasome staining in vivo. This method has been validated by standard post-fixed indirect immunostaining and also allowed co-immunodetection of TPPII and polyubiquitinated proteins under laser scanning confocal microscopy. We found that in the absence of the inhibitor, TPPII is diffusely dispersed within the cytoplasm of C26 cells. The proteasome and ubiquitin-rich perinuclear region failed to display enhanced TPPII staining. However, when proteasome function was impaired by the inhibitor, TPPII associated more closely with both the proteasome and polyubiquitinated proteins via TPPII recruitment to the perinuclear region and subsequently into emerging aggresomal structures. Furthermore, we have demonstrated the dynamic recruitment of TPPII into the developing aggresome: TPPII in the early aggresome was dispersed within the central part but subsequently aggregated on the surface of this structure. In the mature aggresome of C26 cells TPPII formed a spherical mantle, which surrounded the round core containing proteasomes and polyubiquitinated proteins. Our morphological data indicate that TPPII displays spatial localization with proteasomes especially upon proteasome inhibition in aggresomes of C26 cells.
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PMID:Changes in spatio-temporal localization of tripeptidyl peptidase II (TPPII) in murine colon adenocarcinoma cells during aggresome formation: a microscopy study based on a novel fluorescent proteasome inhibitor. 3022 64