Identification of Echinococcus sp Calcineurin: Targets of Eg-FKBP-FK506 Complex

MARÍA CELESTE NICOLAO; ANDREA C. CUMINO

Mar del Plata

Congreso; LVI Reunión Anual de la Sociedad Argentina de Investigación Clínica; 2011

Sociedad Argentina de Investigación Clínica

Calcineurin (CaN) is a eukaryotic Ca-and calmodulin-dependent serine/threonine protein phosphatase (PP2B), potently inhibited by immunosuppressant drugs, CsA and FK506, in the presence of their respective receptor proteins, cyclophilin and FKBP, both described in Echinococcus sp. (Cumino et. al., 2010). Previous experiments in our laboratory have showed that FK506 and CsA possess dose-dependent protoscolicidal activity in E. granulosus. CaN is a heterodimeric protein consisting of a catalytic subunit A, which contains an active site dinuclear metal center and a tightly associated, regulatory Ca-binding subunit B. We identified and analyzed in silico ortologous in Echinococcus genome: Eg-CaN-A and Eg-CaN-B, both archetypal proteins with all residues implicated in the binding of pharmacological ligands, and in interactions with possible targets. The primary sequence of both subunits and heterodimeric quaternary structure is highly conserved in Echinococcus sp. Eg-CaN-A contains a CaM-binding domain (PD343921), a CaN-B-binding domain (PD862669) and an autoinhibitory domain (PD322644). The CaN-B subunit itself is a CaM-like Ca+2-binding protein that contains four high-affinity Ca+2-binding EF hands. Binding of Ca+2 to CaN-B stimulates phosphatase activity, although to a lesser extent than when CaM is also present. Although the estrogen receptor-independent mechanisms of tamoxifen (TAM) remain unclear, it is demonstrated that TAM is implicated in regulates the transcriptional response to calcium. In E. granulosus, protoscolicidal treatment with TAM, showed induction of intracellular calcium release, the alteration of cellular membrane properties and the inhibition of P-glycoprotein (Nicolao et al., 2010). Transcriptional profiling studies showed that TAM reduces the Eg-canB expression, consistently with these observations, in other cellular systems, TAM could involve in the estrogen-dependent regulation of CaN. These findings highlight the potential to define novel drug targets and elucidate conserved elements of signal transduction cascades