Mitochondrial Dysfunction Induced by a Cytotoxic Adenine Dinucleotide Produced by ADP-ribosyl Cyclases from cADPR

Santina Bruzzone,Giuliano Dodoni,Nina Kaludercic,Giovanna Basile,Enrico Millo,Antonio De Flora,Fabio Di Lisa,Elena Zocchi

doi:10.1074/jbc.m609802200

Santina Bruzzone, Giuliano Dodoni + Show 6 more

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https://doi.org/10.1074/jbc.m609802200

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Abstract

ADP-ribosyl cyclases were previously shown to produce three new adenine dinucleotides, P1,P2 diadenosine 5'-diphosphate (Ap2A) and two isomers thereof (P18 and P24), from cyclic ADP-ribose (cADPR) and adenine (Basile, G., Taglialatela-Scafati, O., Damonte, G., Armirotti, A., Bruzzone, S., Guida, L., Franco, L., Usai, C., Fattorusso, E., De Flora, A., and Zocchi, E. (2005) Proc. Natl. Acad. Sci. U. S. A. 102, 14509-14514). The Ap2A isomer P24, containing an unusual C1'-N3 N-glycosidic bond, is shown here to affect mitochondrial function through (i) opening of the permeability transition pore complex (and consequent proton gradient dissipation) and (ii) inhibition of Complex I of the respiratory chain. Whereas proton gradient dissipation is dependent upon the extracellular Ca(2+) influx triggered by P24, the effect on oxygen consumption is Ca(2+) independent. The proton gradient dissipation induces apoptosis in HeLa cells and thus appears to be responsible for the already described potent cytotoxic effect of P24 on several human cell types. The other products of ADP-ribosyl cyclase activity, Ap2A and cADPR, antagonize P24-induced proton gradient dissipation and cytotoxicity, suggesting that the relative concentration of P24, cADPR, and Ap2A in cyclase-positive cells may affect the balance between cell life and death.

Highlights

ADP-ribosyl cyclases (ADPRCs)2 are a family of multifunctional enzymes, present from protists to mammals and higher plants, that generate a number of products affecting the intracellular free calcium concentration ([Ca2ϩ]i), arguably the most influential regulatory signal in cell physiology [1, 2]
The Ca2ϩ-active products of ADPRCs known so far include cyclic ADP-ribose, ADP-ribose (ADPR), nicotinic acid adenine dinucleotide phosphate (NAADPϩ), and the ADP-ribose dimer (ADPR2). cADPR is produced from NADϩ by means of the reaction typical of the ADPRC family that removes the nicotinamide moiety and creates an unusual C1Ј-N1 bond that cyclizes the ADPR molecule [4, 6]. cADPR binds to specific receptor channels on the endoplasmic reticulum, the ryanodine receptors, releasing Ca2ϩ [4, 7, 8]
P24 Cytotoxicity Is Causally Related to the Dissipation of ⌬⌿m—The proton gradient dissipation and the inhibition of Complex I exerted by P24 at concentrations (5–20 ␮M) in the same range as those inducing cytotoxic effects on HeLa cells (Fig. 1B) suggested that the mitochondrial effects of the dinucleotide could be responsible for cell death

Summary

Introduction

ADP-ribosyl cyclases (ADPRCs)2 are a family of multifunctional enzymes, present from protists to mammals and higher plants, that generate a number of products affecting the intracellular free calcium concentration ([Ca2ϩ]i), arguably the most influential regulatory signal in cell physiology [1, 2]. Results obtained demonstrate that mitochondria are a major target of P24 toxicity, with micromolar concentrations of the dinucleotide inducing (i) dissipation of the mitochondrial proton gradient (⌬⌿m) in intact cells through opening of the permeability transition pore (PTP) and (ii) inhibition of the respiratory chain in isolated mitochondria, acting on Complex I.

Results

Conclusion