Inorganic Polyphosphate Inhibits an Aspartic Protease-Like Activity in the eggs of Rhodnius prolixus (Stahl) and Impairs Yolk Mobilization In Vitro

Laboratório de Entomologia Médica, Programa de Biologia Celular e Parasitologia, Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Cidade Universitária, Rio de Janeiro, RJ, Brazil.
Journal of Cellular Physiology (Impact Factor: 3.84). 01/2009; 222(3):606-11. DOI: 10.1002/jcp.21975
Source: PubMed


Inorganic polyphosphate (poly P) is a polymer of phosphate residues that has been shown to act as modulator of some vertebrate cathepsins. In the egg yolk granules of Rhodnius prolixus, a cathepsin D is the main protease involved in yolk mobilization and is dependent on an activation by acid phosphatases. In this study, we showed a possible role of poly P stored inside yolk granules on the inhibition of cathepsin D and arrest of yolk mobilization during early embryogenesis of these insects. Enzymatic assays detected poly P stores inside the eggs of R. prolixus. We observed that micromolar poly P concentrations inhibited cathepsin D proteolytic activity using both synthetic peptides and homogenates of egg yolk as substrates. Poly P was a substrate for Rhodnius acid phosphatase and also a strong competitive inhibitor of a pNPPase activity. Fusion events have been suggested as important steps towards acid phosphatase transport to yolk granules. We observed that poly P levels in those compartments were reduced after in vitro fusion assays and that the remaining poly P did not have the same cathepsin D inhibition activity after fusion. Our results are consistent with the hypothesis that poly P is a cathepsin D inhibitor and a substrate for acid phosphatase inside yolk granules. It is possible that, once activated, acid phosphatase might degrade poly P, allowing cathepsin D to initiate yolk proteolysis. We, therefore, suggest that degradation of poly P might represent a new step toward yolk mobilization during embryogenesis of R. prolixus.

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    • "Here, we measured PolyP mobilization by following DAPI-PolyP fluorescence levels in samples containing PolyP extracted from eggs of the insect R. prolixus during the early stages of development. Results showed that a strong mobilization of PolyP takes place during this period (Figure 7C) and were validated after a comparison against the well-established protocol for PolyP quantification based on the PolyP binding to silica powder in suspension followed by enzymatic PolyP hydrolysis into Pi by a recombinant yeast exopolyphosphatase,14,26,39,53 which showed similar profiles of PolyP mobilization during the early days of development. "
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    • "Although the first evidence for the presence of poly P in mammalian cells was obtained a long time ago 50, relatively few studies have addressed its physiological roles in animal cells 1, 9-12, 14, 18, 42, 51, 52. "
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