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Human metastasis regulator protein H-prune is a short-chain exopolyphosphatase

Marko Tammenkoski1, Katja Koivula, Emilio Cusanelli

  • 1Department of Biochemistry, University of Turku, FIN-20014 Turku, Finland.

Biochemistry
|August 15, 2008
PubMed

Insights

Human protein h-prune acts as an exopolyphosphatase, efficiently hydrolyzing short-chain polyphosphates. Its activity is regulated by nm23-H1 and inorganic polyphosphates, suggesting a role in cancer metastasis.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Enzymology

Background:

  • The DHH superfamily protein h-prune is overexpressed in metastatic cancers and is evolutionarily related to eukaryotic exopolyphosphatases.
  • H-prune binds to the metastasis suppressor nm23-H1, hinting at a potential role in cancer progression.

Purpose of the Study:

  • To investigate the enzymatic activity of human protein h-prune, specifically its potential exopolyphosphatase function.
  • To elucidate the substrate specificity, cofactor requirements, and regulatory mechanisms of h-prune activity.
  • To explore the relationship between h-prune's enzymatic function and its role in cancer metastasis.

Main Methods:

  • Enzyme kinetic assays were performed to determine the hydrolytic activity of h-prune on various polyphosphate substrates.
  • The requirement for divalent metal cofactors (Mg2+, Co2+, Mn2+) was assessed.
  • The effects of potential regulators, including nm23-H1 and different phosphate compounds, on h-prune activity were examined.
  • Site-directed mutagenesis was used to probe the active site residues homologous to yeast exopolyphosphatase.

Main Results:

  • H-prune efficiently hydrolyzes short-chain inorganic polyphosphates (tri- and tetrapolyphosphates) and nucleoside 5'-tetraphosphates, with Michaelis–Menten kinetics.
  • Enzyme activity requires a divalent metal cofactor and is inhibited by nm23-H1, long-chain polyphosphates, and pyrophosphate.
  • Mutagenesis of conserved active site residues significantly reduced or, in one case, enhanced h-prune activity, confirming its exopolyphosphatase function.

Conclusions:

  • H-prune functions as a novel animal exopolyphosphatase, catalyzing the hydrolysis of specific polyphosphate substrates.
  • The activity of h-prune is subject to regulation by nm23-H1 and inorganic polyphosphates, suggesting a role in cellular signaling.
  • These findings support the hypothesis that inorganic polyphosphates modulate the metastatic potential of h-prune in cancer.

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