Down-regulation of proteolytic complexes following EBV activation in BL cells

Structure-Based Design of Fluorogenic Substrates Selective for Human Proteasome Subunits

Proteasomes are established therapeutic targets for hematological cancers and promising targets for autoimmune diseases. In the past, we have designed and synthesized mechanism-based proteasome inhibitors that are selective for the individual catalytic activities of human constitutive proteasomes and immunoproteasomes: β1c, β1i, β2c, β2i, β5c and β5i. We show here that by taking the oligopeptide recognition element and substituting the electrophile for a fluorogenic leaving group, fluorogenic substrates are obtained that report on the proteasome catalytic activity also targeted by the parent inhibitor. Though not generally applicable (β5c and β2i substrates showing low activity), effective fluorogenic substrates reporting on the individual activity of β1c, β1i, β2c and β5i subunits in Raji (human B cell) lysates and purified 20S proteasome were identified in this manner. Our work thus adds to the expanding proteasome research toolbox through the identification of new and/or more effective subunit-selective fluorogenic substrates.

Epstein-Barr virus lytic cycle activation alters proteasome subunit expression in Burkitt's lymphoma cells

We have shown that Epstein-Barr virus (EBV) lytic cycle activation in Burkitt's lymphoma (BL) cells down-regulates chymotrypsin- and caspase-like activities of the proteasome. The aim of the present study was to evaluate whether EBV activation might also affect proteasome subunit composition. Our results indicate that, independently of the latency program established in the host cells, induction of the EBV lytic cycle reduces the expression of the proteasomal components β5, β1 and β2i, whereas it increases that of β2, β1i, PA28α and PA28β. The modulation of the composition and enzymatic activities of the proteolytic complex are indicative of a less efficient generation of viral immunoepitopes.

Inhibition of Poly(ADP-ribose)polymerase impairs Epstein Barr Virus lytic cycle progression

BACKGROUND

Poly(ADP-ribosylation) is a post-translational modification of nuclear proteins involved in several cellular events as well as in processes that characterize the infective cycle of some viruses. In the present study, we investigated the role of poly(ADP-ribosylation) on Epstein-Barr Virus (EBV) lytic cycle activation.

RESULTS

Inhibition of PARP-1 by 3-aminobenzamide (3-ABA) during EBV induction, diminished cell damage and apoptosis in the non-productive Raji cell line while markedly reducing the release of viral particles in the productive Jijoye cells. Furthermore, incubation with 3-ABA up-regulated the levels of LMP1 and EBNA2 latent viral proteins. At the same time, it slightly affected the expression of the immediate early BZLF1 gene, but largely down-regulated the levels of the early BFRF1 protein. The modulation of the expression of both latent and lytic EBV genes appeared to be post-transcriptionally regulated.

CONCLUSION

Taken together the data indicate that PARP-1 plays a role in the progression of EBV lytic cycle and therefore, PARP inhibitors might represent suitable pharmacological adjuncts to control viral spread in EBV productive infection.