Leishmania major: Effect of protein kinase A and phosphodiesterase activity on infectivity and proliferation of promastigotes

Effect of modulators on protein kinase A (PKA) activity, promastigote growth and their ability to infect peritoneal macrophages was monitored. PKA inhibitors reduced [Protein Kinase Inhibitor (PKI) – 56%; H89 – 54.5%] kemptide phosphorylation by Leishmania major promastigote lysates, while activators increased phosphorylation (8-CPT-cAMP – 88%; Sp-cAMPS-AM – 152%). Activation was specifically inhibited by PKI. Phosphodiesterase inhibitors also increased kemptide phosphorylation (dipyridamole – 171%; rolipram – 106%; and 3-isobutyl-1-methyl-xanthine – 154%). Parasite proliferation was significantly retarded (200 nM H89; 100 μM myristoylated-PKI) or completely inhibited (500 nM H89) by culturing with PKA inhibitors. Incubation with dipyridamole or Sp-cAMPS-AM also inhibited proliferation. Brief treatment (2 h) with either H89, myristoylated-PKI, dipyridamole or Sp-cAMPS-AM reduced initial macrophage infection at days 1 and 2 (>40%) and on day 3 (>78% only for 100 μM myr-PKI). Characterization of leishmanial cAMP mediated signal transduction pathways will serve as the basis for the new drug design.