In tumors that retain wild-type p53, its tumor-suppressor function is often impaired as a result of the deregulation of HDM-2, which binds to p53 and targets it for proteasomal degradation. We have screened a chemical library and identified a small molecule named RITA (reactivation of p53 and induction of tumor cell apoptosis), which bound to p53 and induced its accumulation in tumor cells. RITA prevented p53–HDM-2 interaction in vitro and in vivo and affected p53 interaction with several negative regulators. RITA induced expression of p53 target genes and massive apoptosis in various tumor cells lines expressing wild-type p53. RITA suppressed the growth of human fibroblasts and lymphoblasts only upon oncogene expression and showed substantial p53-dependent antitumor effect in vivo. RITA may serve as a lead compound for the development of an anticancer drug that targets tumors with wild-type p53.

The Epstein–Barr virus (EBV) encoded nuclear antigen (EBNA) 1 is expressed in latently infected B lymphocytes that persist for life in healthy virus carriers and is the only viral protein regularly detected in all EBV associated malignancies. The Gly-Ala repeat domain of EBNA1 was shown to inhibit in cis the presentation of major histocompatibility complex (MHC) class I restricted cytotoxic T cell epitopes from EBNA4. It appears that the majority of antigens presented via the MHC I pathway are subject to ATP-dependent ubiquitination and degradation by the proteasome. We have investigated the influence of the repeat on this process by comparing the degradation of EBNA1, EBNA4, and Gly-Ala containing EBNA4 chimeras in a cell-free system. EBNA4 was efficiently degraded in an ATP/ubiquitin/proteasome-dependent fashion whereas EBNA1 was resistant to degradation. Processing of EBNA1 was restored by deletion of the Gly-Ala domain whereas insertion of Gly-Ala repeats of various lengths and in different positions prevented the degradation of EBNA4 without appreciable effect on ubiquitination. Inhibition was also achieved by insertion of a Pro-Ala coding sequence. The results suggest that the repeat may affect MHC I restricted responses by inhibiting antigen processing via the ubiquitin/proteasome pathway. The presence of regularly interspersed Ala residues appears to be important for the effect.

A semiquantitative polymerase chain reaction assay was used to monitor the blood levels of Epstein-Barr virus (EBV)-DNA in 9 patients receiving allogeneic bone marrow transplants (BMT). Four of 5 recipients of HLA-mismatched T-cell–depleted grafts showed a 4- to 5-log increase of EBV-DNA within 1 to 3 months after BMT. Administration of 2 to 4 infusions of 10⁷ EBV-specific cytotoxic T-lymphocytes (CTLs)/m² starting from the time of maximal virus load resulted in a 2- to 3-log decrease of virus titers in 3 patients. One patient, who received a T-cell culture lacking a major EBV-specific component, progressed to fatal EBV-positive lymphoma. Administration of EBV-CTLs before the onset of the EBV-DNA peak resulted in stabilization of the virus titers within 2 to 3 logs above the normal levels in the fifth patient. A moderate increase of virus titers was also detected in 3 of 4 patients receiving unmanipulated HLA-matched grafts, whereas 1 patient with Wiskott-Aldrich syndrome reached a 5-log increase of EBV-DNA load within 70 days after BMT. Our results suggest that a rapid increase of circulating EBV-DNA occurs in the absence of EBV-specific T-cell precursors or in the presence of congenital immune defects that prevent the reestablishment of virus-specific immunity. Prophylactic administration of EBV-CTLs early after BMT appears to provide the most effective protection against the development of EBV-associated lymphoproliferative disease.

Insoluble protein aggregates are consistently found in neurodegenerative disorders caused by expanded polyglutamine [poly(Q)] repeats. The aggregates contain various components of the ubiquitin/proteasome system, suggesting an attempt of the cell to clear the aberrant substrate. To investigate the effect of expanded poly(Q) repeats on ubiquitin/proteasome-dependent proteolysis, we targeted these proteins for proteasomal degradation by the introduction of an N-end rule degradation signal. While soluble poly(Q) proteins were degraded, they resisted proteasomal degradation once present in the aggregates. Stabilization was also observed for proteins that are co-aggregated via interaction with the expanded poly(Q) domain. Introduction of a degradation signal in ataxin-1/Q92 reduced the incidence of nuclear inclusions and the cellular toxicity, conceivably by accelerating the clearance of the soluble substrate.