myo-Inositol hexakisphosphate (IP6) is an abundant intracellular component of animal cells. In this study we describe the presence of extracellular IP6 in the hydatid cyst wall (HCW) of the larval stage of the cestode parasite Echinococcus granulosus. The HCW comprises an inner cellular layer and an outer, acellular (laminated) layer up to 2mm in thickness that protects the parasite from host immune cells. A compound, subsequently identified as IP6, was detected in and purified from an HCW extract on the basis of its capacity to inhibit complement activation. The identification of the isolated compound was carried out by a combination of NMR, MS and TLC. The majority of IP6 in the HCW was found in the acellular layer, with only a small fraction of the compound being extracted from cells. In the laminated layer, IP6 was present in association with calcium, and accounted for up to 15% of the total dry mass of the HCW. IP6 was not detected in any other structures or stages of the parasite. Our results imply that IP6 is secreted by the larval stage of the parasite in a polarized fashion towards the interface with the host. This is the first report of the secretion of IP6, and the possible implications beyond the biology of E. granulosus are discussed.
Abbreviations used: CyPA, cyclophilin A; E-64, trans-epoxysuccinyl-l-leucylamido-(4-guanidino)butane; ECL® (Amersham Biosciences), enhanced chemiluminescence; ER, endoplasmic reticulum; GAG, glycosaminoglycan; HCW, hydatid cyst wall; IP6, myo-inositol hexakisphosphate; IP5, myo-inositol pentakisphosphate; PEI, polyethyleneimine.