Role of protein kinase C-alpha in the control of infection by intracellular pathogens in macrophages

The protein kinase C (PKC) family regulates macrophage function involved in host defense against infection. In this study, we investigated the role of macrophage PKC-alpha in the uptake and subsequent fate of Leishmania donovani promastigotes and Legionella pneumophila infections. To this end, we used clones of the murine macrophage cell line RAW 264.7 overexpressing a dominant-negative (DN) mutant of PKC-alpha. While phagocytosis of L. donovani promastigotes was not affected by DN PKC-alpha overexpression, their intracellular survival was enhanced by 10- to 20-fold at 48 h postinfection. Intracellular survival of a L. donovani mutant defective in lipophosphoglycan repeating units synthesis, which normally is rapidly degraded in phagolysosomes, was enhanced by 100-fold at 48 h postinfection. However, IFN-gamma-induced leishmanicidal activity was not affected by DN PKC-alpha overexpression. Similar to macrophages from genetically resistant C57BL/6 mice, control RAW 264.7 cells were not permissive for the intracellular replication of Legionella pneumophila. In contrast, DN PKC-alpha-overexpressing RAW 264.7 clones were phenotypically similar to macrophages from genetically susceptible A/J mice, as they allowed intracellular replication of L. pneumophila. Permissiveness to L. pneumophila was not the consequence of a general defect in the microbicidal capacities because killing of a temperature-sensitive mutant of Pseudomonas aeruginosa was normal in DN PKC-alpha-overexpressing RAW 264.7 clones. Collectively, these results support a role for PKC-alpha in the regulation of innate macrophage functions involved in the control of infection by intracellular parasites.

Degradation of amyloid A precursor protein SAA by macrophage cell lines obtained from amyloid resistant and susceptible strains of mice

Reactive AA amyloidosis can be induced in mice in a model of sustained inflammation following daily casein subcutaneous injections. However, the development of AA amyloidosis is known to vary in different strains of mice. The C57BL/6 strain is susceptible to the development of amyloidosis while the A/J strain is resistant. The degradation of purified serum amyloid A (SAA) protein by human monocytes as well as by mouse macrophages has been shown. The resistance/susceptibility of different mouse strains to the development of systemic amyloidosis may therefore be related to a difference in the ability of macrophages to degrade SAA. The authors have used bone marrow-derived macrophage cell lines obtained from susceptible C57BL/6 (ANA-1) and resistant A/J (A/J 10) mouse strains to compare their ability to degrade HDL-SAA in vitro. Cells were incubated with HDL-SAA for up to 72 h and the culture medium was analysed by SDS-PAGE to determine the rate of SAA degradation by the macrophages. The A/J 10 cells (resistant) were found to initiate a constant HDL-SAA degradation promptly whereas ANA-1 cells (susceptible) showed an intermittent block in the degradation of the precursor. Activation of macrophages by lipopolysaccharide (LPS) or interferon-gamma (IFN-gamma) hampered the precursor degradation suggesting that the activation process may favour extracellular accumulation of the precursor leading to a partial degradation and fibril formation.