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: 3.87). 01/2009; 222(3):606-11. DOI: 10.1002/jcp.21975
Source: PubMed

ABSTRACT 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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Available from: Ednildo A Machado, Aug 15, 2015
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    • "Other classes of serpins have also been shown to inhibit cysteine and aspartic proteases (Kamada et al. 1997; Liu et al. 2003; Mathialagan and Hansen 1996; Silverman et al. 2004; Takeda et al. 1995) and to regulate cell death processes (Bird et al. 1998; Medema et al. 2001; Suminami et al. 2000; Tewari et al. 1995). We have previously described a role for PolyP in the regulation of an aspartic-like protease in the eggs of Rhodnius prolixus Stahl (Gomes et al. 2010). The role of PolyP regulation in protease-triggered events such as digestion and cell death in the midgut of Anticarsia is currently under investigation in our laboratory. "
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    • "However, further studies will be necessary to assess a more precise function of the enzyme. In the triatomine R. prolixus, cathepsin D and acid phosphatase are involved in a programmed proteolysis of yolk protein throughout embryogenesis (Nussenzveig et al., 1992; Fialho et al., 2002, 2005; Gomes et al., 2010). Therefore, it is plausible that in D. maxima the same enzymatic system would be operative during atresia. "
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    • "It is thus plausible that PolyPs also play major roles in invertebrate physiology. Accordingly, involvement of PolyP with the regulation of proteases (Gomes et al., 2010; Kuroda et al., 2001) and energy supply (Campos et al., 2007) has been proposed in invertebrate eggs. In the present report, we identified spherites from epithelial cells of A. gemmatalis Fig. 3. PolyP quantification and elemental composition of spherites. "
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