Biomedical subjects

Anna Borodovsky

Publications and source records attributed to Anna Borodovsky.

4 recordsLinked to original sources

PubMed2002

Pathways accessory to proteasomal proteolysis are less efficient in major histocompatibility complex class I antigen production.

Degradation of cytosolic proteins depends largely on the proteasome, and a fraction of the cleavage products are presented as major histocompatibility complex (MHC) class I-bound ligands at the cell surface of antigen presenting cells. Proteolytic pathways accessory to the proteasome contribute to protein turnover, and their up-regulation may complement the proteasome when proteasomal proteolysis is impaired. Here we show that reduced reliance on proteasomal proteolysis allowed a reduced efficiency of MHC class I ligand production, whereas protein turnover and cellular proliferation were maintained. Using the proteasomal inhibitor adamantane-acetyl-(6-aminohexanoyl)3-(leucinyl)3-vinyl-(methyl)-sulphone, we show that covalent inhibition of all three types of proteasomal beta-subunits (beta(1), beta(2), and beta(5)) was compatible with continued growth in cells that up-regulate accessory proteolytic pathways, which include cytosolic proteases as well as deubiquitinating enzymes. However, under these conditions, we observed poor assembly of H-2D(b) molecules and inhibited presentation of endogenous tumor antigens. Thus, the tight link between protein turnover and production of MHC class I ligands can be broken by enforcing the substitution of the proteasome with alternative proteolytic pathways.

Animals↗

PubMed2002

The ubiquitin-proteasome pathway in thymocyte apoptosis: caspase-dependent processing of the deubiquitinating enzyme USP7 (HAUSP).

Programmed cell death (apoptosis) is crucial for thymocyte development. We analyzed the role of the ubiquitin (Ub)-proteasome pathway in dexamethasone-triggered and TCR-mediated apoptosis in fetal thymic organ culture (FTOC). Proteasome activity was increased in apoptotic thymocytes, as visualized by active-site labeling of proteasomal beta subunits. The activity of deubiquitinating enzymes in murine apoptotic thymocytes was likewise examined by active-site labeling. We show that the deubiquitinating enzyme USP7 (HAUSP) is proteolytically processed upon dexamethasone-, gamma-irradiation-, and antigen-induced cell death. Such processing of HAUSP does not occur in caspase 3-/- thymocytes, or upon pretreatment of wild type thymocytes with the general caspase inhibitor ZVAD-fmk. Thus, our results suggest that thymocyte apoptosis leads to modification of deubiquitinating enzymes by caspase activity and may provide an additional link between the ubiquitin-proteasome pathway and the caspase cascade during programmed cell death.

Amino Acid Chloromethyl Ketones↗

PubMed2002

Chemistry-based functional proteomics reveals novel members of the deubiquitinating enzyme family.

The ubiquitin (Ub)-proteasome system includes a large family of deubiquitinating enzymes (DUBs). Many members are assigned to this enzyme class by sequence similarity but without evidence for biological activity. A panel of novel DUB-specific probes was generated by a chemical ligation method. These probes allowed identification of DUBs and associated components by tandem mass spectrometry, as well as rapid demonstration of enzymatic activity for gene products whose functions were inferred from primary structure. We identified 23 active DUBs in EL4 cells, including the tumor suppressor CYLD1. At least two DUBs tightly interact with the proteasome 19S regulatory complex. An OTU domain-containing protein, with no sequence homology to any known DUBs, was isolated. We show that this polypeptide reacts with the C terminus of Ub, thus demonstrating DUB-like enzymatic activity for this novel superfamily of proteases.

Animals↗

PubMed2002

Multiple associated proteins regulate proteasome structure and function.

We have identified proteins that are abundant in affinity-purified proteasomes, but absent from proteasomes as previously defined because elevated salt concentrations dissociate them during purification. The major components are a deubiquitinating enzyme (Ubp6), a ubiquitin-ligase (Hul5), and an uncharacterized protein (Ecm29). Ecm29 tethers the proteasome core particle to the regulatory particle. Proteasome binding activates Ubp6 300-fold and is mediated by the ubiquitin-like domain of Ubp6, which is required for function in vivo. Ubp6 recognizes the proteasome base and its subunit Rpn1, suggesting that proteasome binding positions Ubp6 proximally to the substrate translocation channel. ubp6Delta mutants exhibit accelerated turnover of ubiquitin, indicating that deubiquitination events catalyzed by Ubp6 prevent translocation of ubiquitin into the proteolytic core particle.

Adenosine Triphosphate↗