Identifying Glyceraldehyde 3-Phosphate Dehydrogenase as a Cyclic Adenosine Diphosphoribose Binding Protein by Photoaffinity Protein-Ligand Labeling Approach

Cyclic adenosine diphosphoribose (cADPR), an endogenous nucleotide derived from nicotinamide adenine dinucleotide (NAD+), mobilizes Ca2+ release from endoplasmic reticulum (ER) via ryanodine receptors (RyRs), yet the bridging protein(s) between cADPR and RyRs remain(s) unknown. Here we synthesized a novel photoaffinity labeling (PAL) cADPR agonist, PAL-cIDPRE, and subsequently applied it to purify its binding proteins in human Jurkat T cells. We identified glyceraldehyde 3-phosphate dehydrogenase (GAPDH) as one of the cADPR binding protein(s), characterized the binding affinity between cADPR and GAPDH in vitro by surface plasmon resonance (SPR) assay, and mapped cADPR's binding sites in GAPDH. We further demonstrated that cADPR induces the transient interaction between GAPDH and RyRs in vivo and that GAPDH knockdown abolished cADPR-induced Ca2+ release. However, GAPDH did not catalyze cADPR into any other known or novel compound(s). In summary, our data clearly indicate that GAPDH is the long-sought-after cADPR binding protein and is required for cADPR-mediated Ca2+ mobilization from ER via RyRs.

Role of kidney ADP-ribosyl cyclase in diabetic nephropathy

The role of ADP-ribosyl cyclases (ADPR-cyclases) in diabetic nephropathy was investigated. ADPR-cyclases synthesize cADP-ribose (cADPR), a Ca(2+)-mobilizing second messenger, and are stimulated by G protein-coupled receptors. We have previously reported that ADPR-cyclases can be activated by ANG II and showed that a specific kidney ADPR-cyclase inhibitor, 4,4'-dihydroxyazobenzene (DHAB), can protect ANG II-mediated mesangial cell growth (Kim SY, Gul R, Rah SY, Kim SH, Park SK, Im MJ, Kwon HJ, Kim UH. Am J Physiol Renal Physiol 294: F982-F989, 2008). In this study, we examined the preventive effect of DHAB on glomerular injury in streptozotocin (STZ)-induced diabetic mice. Male mice were randomly assigned to normal control and diabetic groups of comparable age. A diabetic group received 45 microg/kg of DHAB for 6 wk via daily intraperitoneal injections. Several nephropathy parameters were improved in the DHAB-treated diabetic group compared with the diabetic group, including urinary albumin (diabetic, 44.6 +/- 5.1 vs. treated, 33.9 +/- 3.9 microg/day), creatinine clearance (diabetic, 0.72 +/- 0.03 vs. treated, 0.83 +/- 0.04 ml.min(-1).100 g(-1)), ratio of kidney to body weight (diabetic, 2.5 +/- 0.04 vs. treated, 1.4 +/- 0.04), and mesangial matrix expansion (diabetic, 13.9 +/- 2.2 vs. treated, 8.5 +/- 2.0%). These results indicate that kidney function in STZ-induced diabetes was improved by DHAB administration. Furthermore, DHAB inhibited phosphorylation of Akt and nuclear factor of activated T cell 3 nuclear translocation, as well as ADPR-cyclase activity and cADPR production, which were increased in the kidneys of the diabetic group. In addition, DHAB treatment decreased fibrosis marker protein expression and glomerular hypertrophy in the diabetic kidney. These findings indicate a crucial role that ADPR-cyclase signaling plays in the renal pathogenesis of diabetes and provide a therapeutic tool for the treatment of renal diseases.

Molecular mechanism of ADP-ribosyl cyclase activation in angiotensin II signaling in murine mesangial cells

ADP-ribosyl cyclase (ADPR-cyclase) produces a Ca(2+)-mobilizing second messenger cyclic ADP-ribose (cADPR) from NAD(+). In this study, we investigated the molecular basis of ADPR-cyclase activation and the following cellular events in angiotensin II (ANG II) signaling in mouse mesangial cells (MMCs). Treatment of MMCs with ANG II induced an increase in intracellular Ca(2+) concentrations through a transient Ca(2+) release via an inositol 1,4,5-trisphosphate receptor and a sustained Ca(2+) influx via L-type Ca(2+) channels. The sustained Ca(2+) signal, but not the transient Ca(2+) signal, was blocked by a cADPR antagonistic analog, 8-bromo-cADPR (8-Br-cADPR), and an ADPR-cyclase inhibitor, 4,4'-dihydroxyazobenzene (DHAB). In support of the results, ANG II stimulated cADPR production in a time-dependent manner, and DHAB inhibited ANG II-induced cADPR production. Application of pharmacological inhibitors revealed that activation of ADPR-cyclase by ANG II involved ANG II type 1 receptor, phosphoinositide 3-kinase, protein tyrosine kinase, and phospolipase C-gamma1. Moreover, DHAB as well as 8-Br-cADPR abrogated ANG II-mediated Akt phosphorylation, nuclear translocation of nuclear factor of activated T cell, and uptake of [(3)H]thymidine and [(3)H]leucine in MMCs. These results demonstrate that ADPR-cyclase in MMCs plays a pivotal role in ANG II signaling for cell proliferation and protein synthesis.