CHARACTERIZATION OF CALCINEURIN FROM HYMENOLEPIS-MICROSTOMA AND H-DIMINUTA AND ITS INTERACTION WITH CYCLOSPORINE-A

The drug cyclosporin A (CsA) exerts its immunosuppressive action by bi nding to the cytosolic protein, cyclophilin (CyP) and, as a complex, b inding to and inhibiting the calcium/calmodulin-dependent serine threo nine phosphatase, calcineurin. It is unknown whether a similar mode of action occurs during the drug's antiparasite activity. Calmodulin-bin ding proteins from the helminth parasites Hymenolepis microstoma and H . diminuta were purified by affinity chromatography, yielding single p olypeptide bands of 60 000 M(r), according to SDS-PAGE. These proteins were tested for calcineurin activity by the dephosphorylation of the R(II) peptide (part of the catalytic subunit of cAMP-dependent protein kinase). Both proteins were calcium- and calmodulin-dependent and wer e inhibited by mammalian cyclophilin complexed with cyclosporin A (IC5 0 values of 0 . 75 mu g CyP for H. microstoma and 0 . 90 mu g CyP for H. diminuta). However, neither of the parasite calcineurins was inhibi ted by H. microstoma cyclophilin/CsA. These data suggest the anthelmin tic mode of action of CsA in these helminth models does not involve th e inhibition of a signal transduction pathway requiring interaction wi th calcineurin.