Use of anti-cancer drugs, mitocans, to enhance the immune responses against tumors.

Cytotoxic drugs in cancer therapy are used with the expectation of selectively killing and thereby eliminating the offending cancer cells. If they should die in an appropriate manner, the cells can also release danger signals that promote an immune reaction that reinforces the response against the cancer. The identity of these immune-enhancing danger signals, how they work extra- and intracellularly, and the molecular mechanisms by which some anti-cancer drugs induce cell death to bring about the release of danger signals are the major focus of this review. A specific group of mitocans, the vitamin E analogs that act by targeting mitochondria to drive ROS production and also promote a more immunogenic means of cancer cell death exemplify such anti-cancer drugs. The role of reactive oxygen species (ROS) production and the events leading to the activation of the inflammasome and pro-inflammatory mediators induced by dying cancer cell mitochondria are discussed along with the evidence for their contribution to promoting immune responses against cancer. Current knowledge of how the danger signals interact with immune cells to boost the anti-tumor response is also evaluated.

A novel active site-directed probe specific for deubiquitylating enzymes reveals proteasome association of USP14.

A C-terminally modified ubiquitin (Ub) derivative, ubiquitin vinyl sulfone (UbVS), was synthesized as an active site-directed probe that irreversibly modifies a subset of Ub C-terminal hydrolases (UCHs) and Ub-specific processing proteases (UBPs). Specificity of UbVS for deubiquitylating enzymes (DUBs) is demonstrated not only by inhibition of [(125)I]UbVS labeling with N-ethylmaleimide and Ub aldehyde, but also by genetic analysis. [(125)I]UbVS modifies six of the 17 known and putative yeast deubiquitylating enzymes (Yuh1p, Ubp1p, Ubp2p, Ubp6p, Ubp12p and Ubp15p), as revealed by analysis of corresponding mutant strains. In mammalian cells, greater numbers of polypeptides are labeled, most of which are likely to be DUBs. Using [(125)I]UbVS as a probe, we report the association of an additional DUB with the mammalian 26S proteasome. In addition to the 37 kDa enzyme reported to be part of the 19S cap, we identified USP14, a mammalian homolog of yeast Ubp6p, as being bound to the proteasome. Remarkably, labeling of 26S-associated USP14 with [(125)I]UbVS is increased when proteasome function is impaired, suggesting functional coupling between the activities of USP14 and the proteasome.

Integration of the ubiquitin-proteasome pathway with a cytosolic oligopeptidase activity.

Cytosolic proteolysis is carried out predominantly by the proteasome. We show that a large oligopeptidase, tripeptidylpeptidase II (TPPII), can compensate for compromised proteasome activity. Overexpression of TPPII is sufficient to prevent accumulation of polyubiquitinated proteins and allows survival of EL-4 cells at otherwise lethal concentrations of the covalent proteasome inhibitor NLVS (NIP-leu-leu-leu-vinylsulfone). Elevated TPPII activity also partially restores peptide loading of MHC molecules. Purified proteasomes from adapted cells lack the chymotryptic-like activity, but still degrade longer peptide substrates via residual activity of their Z subunits. However, growth of adapted cells depends on induction of other proteolytic activities. Therefore, cytosolic oligopeptidases such as TPPII normalize rates of intracellular protein breakdown required for normal cellular function and viability.

BAP1: a novel ubiquitin hydrolase which binds to the BRCA1 RING finger and enhances BRCA1-mediated cell growth suppression.

We have identified a novel protein, BAP1, which binds to the RING finger domain of the Breast/Ovarian Cancer Susceptibility Gene product, BRCA1. BAP1 is a nuclear-localized, ubiquitin carboxy-terminal hydrolase, suggesting that deubiquitinating enzymes may play a role in BRCA1 function. BAP1 binds to the wild-type BRCA1-RING finger, but not to germline mutants of the BRCA1-RING finger found in breast cancer kindreds. BAP1 and BRCA1 are temporally and spatially co-expressed during murine breast development and remodeling, and show overlapping patterns of subnuclear distribution. BAP1 resides on human chromosome 3p21.3; intragenic homozygous rearrangements and deletions of BAP1 have been found in lung carcinoma cell lines. BAP1 enhances BRCA1-mediated inhibition of breast cancer cell growth and is the first nuclear-localized ubiquitin carboxy-terminal hydrolase to be identified. BAP1 may be a new tumor suppressor gene which functions in the BRCA1 growth control pathway.