Proteolysis of P6.9 Induced by Cytochalasin D in Autographa Californica M Nuclear Polyhedrosis Virus-infected Cells

Cytochalasin D, a fungus-derived compound that interferes with actin polymerization, inhibits Autographa californica M nuclear polyhedrosis virus production in infected Spodoptera frugiperda (IPLB-Sf-21) cells. Cytochalasin D appears to inhibit nucleocapsid morphogenesis by interfering with nucleoprotein packaging. We were interested in determining, therefore, whether the drug affected the synthesis or processing of p6.9, the major core protein involved in nucleoprotein packaging. We found that cytochalasin D had no effect on the synthesis, phosphorylation, or dephosphorylation of p6.9, but that it induced the proteolysis of p6.9, an effect which could account for the inhibition of nucleocapsid morphogenesis. We also determined that the cytochalasin D-induced proteolysis of p6.9 was reversible upon removal of the drug, even in the absence of protein synthesis.