Protein phosphorylation in murine peritoneal macrophages induced by infection with Salmonella species.

Infection of peritoneal macrophages from C3H/HeN and C3H/HeJ mice with Salmonella typhimurium or S. enteritidis induced extensive phosphorylation in a set of proteins with molecular masses of 85, 72, 35, 30, and 23 kDa, which were different from those induced by bacterial lipopolysaccharide. The phosphorylated proteins of 35, 30, and 23 kDa (pp35, pp30, and pp23, respectively) originated from the infecting bacteria, because living bacteria could induce these phosphorylated proteins themselves, and no induction of the proteins occurred in macrophages after phagocytosis of heat-killed or UV-irradiated organisms. When the infected macrophages were disrupted and separated into bacterial and macrophage debris fractions, pp85 and pp72 remained in the macrophage debris fraction, with none in the bacterial fraction. Induction of pp85 and pp72 in infected macrophages was inhibited in the presence of chloramphenicol but not cytochalasin D, suggesting that bacterial growth in the macrophages is necessary for induction of both proteins. Neither of these proteins could be detected in macrophages infected with Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, or Listeria monocytogenes. These results support the view that phosphorylation of the 85- and 72-kDa proteins occurs in the macrophages during the early phases of the interaction between Salmonella organisms and macrophages. The functions of specific proteins remain to be clarified.