Stage-Specific Expression and Subcellular Localization of Calcineurin in Infective Forms of Leishmania amazonensis

Calcineurin (CaN), a Ca²⁺-dependent phosphatase, plays key roles in eukaryotic cell signaling. We investigated whether <i>Leishmania amazonensis</i>' two infective forms-promastigotes and amastigotes-exhibit differences in CaN expression, localization, and functional impact, using two canonical inhibitors (cyclosporin A, CsA; tracolimus, FK506). At high 40 µM CsA, promastigotes showed reduced viability, whereas amastigotes remained resistant. FK506 had no effect on either form. At a sub-lethal 25 µM CsA, parasite proliferation remained unaffected. In parasite-macrophage co-incubation assays, phosphorylation patterns differed: amastigotes-but not promastigotes-showed increased serine/threonine phosphorylation upon CaN inhibition. Western blotting and in silico data revealed higher CaN catalytic (CaNA2) and regulatory (CaNB) subunit expression in amastigotes than promastigotes. Immunofluorescence localized CaNA prominently in both cytoplasm and nucleus of promastigotes, but predominantly cytoplasmic in amastigotes; CaNB was largely cytoplasmic in both. In silico localization predictions suggested strong membrane associations for CaNA in <i>Leishmania</i>, contrasting with mammalian models. Subcellular fractionation confirmed CaNA enrichment in membrane fractions, with CaNB in cytoplasmic and nuclear fractions. Collectively, these findings reveal form-specific differences in expression, subcellular distribution, and inhibitor responses of CaN in <i>L. amazonensis</i>, highlighting its potential as a stage-specific therapeutic target in leishmaniasis.