Novel partner proteins of adenovirus penton.

Each of the 12 vertices of the adenovirus virion is made of penton, the complex of two oligomeric proteins: a pentameric penton base anchored in the capsid and an antenna-like trimeric fiber extending outwards. Adenovirus penton plays an essential role in the infection of host cells because it is indispensable for virus attachment and internalization. The initial interactions of penton with the primary and secondary receptors are well described. In contrast with that, the role of the penton components downstream of the initial cell contact is not known. This work shows for the first time that two adenovirus structural proteins, fiber and base, are able to interact intimately with different classes of cellular targets. In the case of penton base, a protein responsible for virus internalization, the partners include three ubiquitin-protein ligases that are involved in protein turnover, cell cycle control and endocytosis. Another base protein partner, BAG3, is involved in controlling Hsc70 chaperone activity. Virus attachment protein, fiber, interacts with many different partners, some of them involved in signal transduction and cell growth. Further work will illustrate the implications of these interactions for both the viral and cellular life cycles.

Toxoplasma gondii: role of the phosphatidylcholine-specific phospholipase C during cell invasion and intracellular development.

The effect of D609, a specific inhibitor of phosphatidylcholine-specific phospholipase C, was investigated on cyst development of the Prugniaud strain of Toxoplasma gondii in vitro. Following treatment with the inhibitor 24 h after cell infection, cyst development was affected as assessed by staining with the bradyzoite-specific mAb CC2: the CC2-reactive antigen was shown to be differently located (in the wall versus the matrix under control conditions). This correlated with a decrease in parasite multiplication induced by D609. Pretreatment of the parasites with D609 inhibited their entry into the host cells, whereas pretreatment of the host cells enhanced the intracellular multiplication of the para sites, without any effect on cell invasion or cyst formation. Our results suggest a crucial role for phosphatidylcholine-specific phospholipase C in the pathophysiology of toxoplasmosis.