Effect of influenza virus on protein phosphorylation in isolated membranes of chick embryo cells.

Membranes isolated from chick embryo cells (CEC) were found to contain an endogenous protein kinase that phosphorylated endogenous proteins. 32P incorporation into membrane proteins was analysed by sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE) and detected by autoradiography. Membrane phosphorylation in the presence of physiological saline (PM-phys) and in the presence of influenza virus (PM-V) were compared. Under short-time incubation (less than 1 min) with gamma-32P ATP there was practically no difference between PM-phys and PM-V in 32P incorporation. Under prolonged incubation (3-15 min), gradual dephosphorylation of the phosphoprotein moving in SDS-PAGE in the zone of relative molecular mass (Mr) of 60 kDa (phosphoprotein P60) was observed in PM-phys whereas in PM-V, phosphorylation of P60 increased with the time of incubation with gamma-32P ATP. Dephosphorylation of P60 in PM-phys was inhibited by 2.5 mmol/l EGTA as well as by 100 mumol/l chlorpromazine (CPZ) and stimulated by calmodulin (CaM) in the presence of Ca2+. Responsible for the dephosphorylation was probably the endogenous Ca2+ and/or CaM-dependent membrane protein phosphatase. It was inhibited by influenza virus (even in the presence of Ca2+ and CaM). The possible role of P60 phosphorylation in the first step of virus infection is discussed.