Nicotinate Adenine Dinucleotide Phosphate (NAADP) Triggers a Specific Calcium Release System in Sea Urchin Eggs

Abstract

Transient fluxes of intracellular ionized calcium (Ca2+) from intracellular stores are integral components of regulatory signaling pathways operating in numerous biological regulations, including in early stages of egg fertilization. Therefore, we explored whether NADP, which is rapidly generated by phosphorylation of NAD upon fertilization may, directly or indirectly, exert a regulatory role as a trigger of Ca2+ release from intracellular stores in sea urchin eggs. NADP had no effect, but we found that the deamidated derivative of NADP, nicotinate adenine dinucleotide phosphate (beta-NAADP), is a potent and specific stimulus (ED50 16 nM) for Ca2+ release in sea urchin egg homogenates. NAADP triggers the Ca2+ release via a mechanism which is distinct from the well-known Ca2+ release systems triggered either by inositol-1,4,5-triphosphate (IP3) or by cyclic adenosine diphospho-ribose (cADPR). The NAADP-induced release of Ca2+ is not blocked by heparin, an antagonist of IP3, or by procaine or ruthenium red, antagonists of cADPR. However, it is selectively blocked by thionicotinamide-NADP which does not inhibit the actions of IP3 or cADPR. NAADP produced by heating of NADP in alkaline (pH = 12) medium or synthetized enzymatically by nicotinic acid-NADP reaction catalyzed by NAD glycohydrolase have identical properties. The results presented herein thus describe a novel endocellular Ca(2+)-releasing system controlled by NAADP as a specific stimulus. The NAADP-controlled Ca2+ release system may be an integral component of multiple intracellular regulations occurring in fertilized sea urchin eggs, which are mediated by intracellular Ca2+ release, and may also have similar role(s) in other tissues.

Calcium signals regulated by NAADP and two-pore channels - their role in development, differentiation and cancer

“…Unlike cADPR-and InsP 3 -mediated Ca 2+ release, NAADP-induced Ca 2+ release is insensitive to changes in cytosolic Ca 2+ concentration or Ca 2+ chelation, indicating that the target receptor for NAADP is not subject to Ca 2+ -induced Ca 2+ -release (CICR) (Chini and Dousa 1996). In urchin egg homogenates, NAADP-evoked Ca 2+ release is not affected by blockers of cADPRor IP 3 -induced Ca 2+ release, 8-NH 2 -cADPR or heparin (Lee and Aarhus 1995), ER Ca 2+ depletion by thapsigargin (Genazzani et al, 1996), or prior Ca 2+ release by cADPR or IP 3 (Chini et al, 1995), but is desensitised by prior NAADP-induced Ca 2+ release (Lee and Aarhus 1995). In addition, prior exposure to non-Ca 2+ -releasing concentrations of NAADP has been shown to desensitise urchin egg homogenates to subsequent release by activating concentrations (Genazzani et al, 1996).…”

Calcium release from the endoplasmic reticulum of higher plants elicited by the NADP metabolite nicotinic acid adenine dinucleotide phosphate

“…Separation of sea urchin microsomes on Percoll gradients has demonstrated that the InsP 3 -and cADPR-dependent Ca 2ϩ release pathways coreside in the same fraction, whereas the NAADPsensitive vesicles are scattered throughout various fractions (39). However, the precise membrane location of the NAADPsensitive Ca 2ϩ pool could not be defined (12,50). It is interesting to note that the distribution of ligand-sensitive Ca 2ϩ pools share similar patterns in both sea urchins and plants, whereby InsP 3 -and cADPR-gated channels coreside on the same membrane type, ER in the case of sea urchins and the vacuolar membrane in the case of plants.…”

“…The two Ca 2ϩ -mobilizing agents cADPR and NAADP, although structurally related (36) and produced by the same ADP-ribosyl cyclase activity (37), trigger Ca 2ϩ release through independent mechanisms in sea urchin eggs (9,12). To ascertain whether the NAADP-dependent Ca 2ϩ release pathway is distinct from that activated by cADPR in plant cells, Ca 2ϩ -loaded beet microsomes were treated with saturating doses (1 M) of cADPR and subsequently NAADP.…”

“…More recently, nicotinic acid adenine dinucleotide phosphate (NAADP), a metabolite of NADP, also has been identified as a potent mobilizer of Ca 2ϩ in sea urchin eggs, pancreatic acinar cells, and brain (9)(10)(11). Pharmacological and fractionation studies (9,11,12) demonstrate that both the release mechanism and the Ca 2ϩ stores sensitive to NAADP are distinct from those that are sensitive to InsP 3 and cADPR. NAADP-dependent Ca 2ϩ release also displays biochemical features not found in the other two ligand-gated systems.…”

Nicotinic Acid Adenine Dinucleotide Phosphate-induced Ca2+ Release

“…NAADP ϩ releases Ca 2ϩ via a mechanism distinct from those triggered by Ins-P 3 and cADPr because: (i) the antagonists heparin and 8-NH 2 -cADPr do not block NAADP ϩ -induced Ca 2ϩ release (4); (ii) desensitization of Ins-P 3 and ryanodine receptors does not influence NAADP ϩ -induced Ca 2ϩ release (4,5); and, (iii) NAADP ϩ -induced Ca 2ϩ release appears to be additive to that induced by Ins-P 3 or cADPr. (7).…”