FUNCTIONALITY AND CELL ANCHORAGE DEPENDENCE OF THE AFRICAN SWINE FEVER VIRUS GENE A179L, A VIRAL BCL-2 HOMOLOG, IN INSECT CELLS

The African swine fever virus gene A179L has been shown to be a functi onal member of the ced9/bcl-2 family of apoptosis inhibitors in mammal ian cell lines. In this work we have expressed the A179L gene product (p21) under the control of the baculovirus polyhedrin promoter using a baculovirus system. Expression of the A179L gene neither altered the baculovirus replication phenotype nor delayed the shutoff of cellular protein synthesis, but it extended the survival of the infected insect cells to very late times postinfection. The increase in cell survival rates correlated with a marked apoptosis reduction after baculovirus infection. Interestingly, prevention of apoptosis was observed when re combinant baculovirus infections were carried out in monolayer cell cu ltures but not when cells were infected in suspension, suggesting a ce ll anchorage dependence for p21 function in insect cells. Cell surviva l was enhanced under optimal conditions of cell attachment and cell-to -cell contact as provided by extracellular matrix components or poly-D -lysine. Since it was observed that cytoskeleton organization varied d epending on culture conditions of insect cells (grown in monolayer ver sus grown in suspension), these results suggested that A179L might reg ulate apoptosis in insect cells only when the cytoskeletal support of intracellular signaling is maintained upon cell adhesion. Thus, cell s hape and cytoskeleton status might allow variations in intracellular t ransduction of signals related to cell survival in virus-infected cell s.