Koji Nata

Cyclic ADP-ribose Binds to FK506-binding Protein 12.6 to Release Ca2+ from Islet Microsomes

Cyclic ADP-ribose (cADPR) is a second messenger for Ca2+ mobilization via the ryanodine receptor (RyR) from islet microsomes for insulin secretion (Takasawa, S., Nata, K., Yonekura, H., and Okamoto, H. (1993) Science 259, 370-373). In the present study, FK506, an immunosuppressant that prolongs allograft survival, as well as cADPR were found to induce the release of Ca2+ from islet microsomes. After islet microsomes were treated with FK506, the Ca2+ release by cADPR from microsomes was reduced. cADPR as well as FK506 bound to FK506-binding protein 12.6 (FKBP12.6), which we also found occurs naturally in islet microsomes. When islet microsomes were treated with cADPR, FKBP12.6 dissociated from the microsomes and moved to the supernatant, releasing Ca2+ from the intracellular stores. The microsomes that were then devoid of FKBP12.6 did not show Ca2+ release by cADPR. These results strongly suggest that cADPR may be the ligand for FKBP12.6 in islet RyR and that the binding of cADPR to FKBP12.6 frees the RyR from FKBP12.6, causing it to release Ca2+.

Regulatory role of CD38 (ADP-ribosyl cyclase/cyclic ADP-ribose hydrolase) in insulin secretion by glucose in pancreatic beta cells. Enhanced insulin secretion in CD38-expressing transgenic mice.

Cyclic ADP-ribose (cADPR) serves as a second messenger for Ca2+ mobilization in insulin secretion, and CD38 has both ADP-ribosyl cyclase and cADPR hydrolase activities (Takasawa, S., Tohgo, A., Noguchi, N., Koguma, T., Nata, K., Sugimoto, T., Yonekura, H., and Okamoto, H.(1993) J. Biol. Chem. 268, 26052-26054). Here, we produced transgenic mice overexpressing human CD38 in pancreatic β cells. The enzymatic activity of CD38 in transgenic islets was greatly increased, and ATP efficiently inhibited the cADPR hydrolase activity. The Ca2+ mobilizing activity of cell extracts from transgenic islets incubated in high glucose was 3-fold higher than that of the control, suggesting that ATP produced by glucose metabolism increased cADPR accumulation in transgenic islets. Glucose- and ketoisocaproate-induced but not tolbutamide- nor KCl-induced insulin secretions from transgenic islets were 1.7-2.3-fold higher than that of control. In glucose-tolerance tests, the transgenic serum insulin level was higher than that of control. The present study provides the first evidence that CD38 has a regulatory role in insulin secretion by glucose in β cells, suggesting that the Ca2+ release from intracellular cADPR-sensitive Ca2+ stores as well as the Ca2+ influx from extracellular sources play important roles in insulin secretion.

Autoantibodies against CD38 (ADP-ribosyl cyclase/cyclic ADP-ribose hydrolase) that impair glucose-induced insulin secretion in noninsulin- dependent diabetes patients.

Cyclic ADP-ribose (cADPR) has been shown to be a mediator for intracellular Ca2+ mobilization for insulin secretion by glucose in pancreatic beta cells, and CD38 shows both ADP-ribosyl cyclase to synthesize cADPR from NAD+ and cADPR hydrolase to hydrolyze cADPR to ADP-ribose. We show here that 13.8% of Japanese non-insulin-dependent diabetes (NIDDM) patients examined have autoantibodies against CD38 and that the sera containing anti-CD38 autoantibodies inhibit the ADP-ribosyl cyclase activity of CD38 (P </= 0.05). Insulin secretion from pancreatic islets by glucose is significantly inhibited by the addition of the NIDDM sera with anti-CD38 antibodies (P </= 0.04-0.0001), and the inhibition of insulin secretion is abolished by the addition of recombinant CD38 (P </= 0.02). The increase of cADPR levels in pancreatic islets by glucose was also inhibited by the addition of the sera (P </= 0.05). These results strongly suggest that the presence of anti-CD38 autoantibodies in NIDDM patients can be one of the major causes of impaired glucose-induced insulin secretion in NIDDM.

A missense mutation in the CD38 gene, a novel factor for insulin secretion: association with Type II diabetes mellitus in Japanese subjects and evidence of abnormal function when expressed in vitro

Summary Cyclic adenosine 5′diphosphate-ribose (cADPR) is thought to have a second messenger role in insulin secretion through mobilisation of Ca2 +. As human lymphocyte antigen CD38 has both ADP-ribosyl cyclase and cADPR hydrolase activity, it may be important in glucose-induced insulin secretion in islets. Thirty one randomly selected Japanese patients with Type II diabetes mellitus who had first-degree and/or second-degree relative(s) with Type II diabetes mellitus were screened for mutations of this gene using single-stranded conformation polymorphism. Two variant patterns in exon 3 and exon 4 of the CD38 gene were identified. The variant in exon 3 resulted in an amino acid substitution from Arg140 (CGG) to Trp (TGG). The Arg140Trp mutation was observed in 4 of 31 patients, and allele frequencies were significantly different in patients and the control subjects (p = 0.004). One patient with this mutation has two missense mutations on beta cell/liver glucose transporter (GLUT2) gene; her mother, who has impaired glucose tolerance, also has this mutation on the CD38 gene and one missense mutation on the GLUT2 gene. Enzyme activity studies using COS-7 cells expressing the Arg140Trp mutation showed a reduction in ADP-ribosyl cyclase and cADPR hydrolase activity of around 50 %. The Arg140Trp mutation on CD38 thus appears to contribute to the development of Type II diabetes mellitus via the impairment of glucose-induced insulin secretion in the presence of other genetic defects. [Diabetologia (1998) 41: 1024–1028]

Cyclin D1 activation through ATF-2 in Reg-induced pancreatic β-cell regeneration

Regenerating gene product (Reg) is induced in pancreatic β‐cells and acts as an autocrine/paracrine growth factor for regeneration via a cell surface Reg receptor. However, the manner by which Reg induces β‐cell regeneration was unknown. In the present study, we found that Reg increased phospho‐ATF‐2, which binds to −57 to −52 of the cyclin D1 gene to activate the promoter. The Reg/ATF‐2‐induced cyclin D1 promoter activation was attenuated by PI(3)K inhibitors such as LY294002 and wortmannin. In Reg knockout mouse islets, the levels of phospho‐ATF‐2, cyclin D1, and phospho‐Rb were greatly decreased. These results indicate that the Reg–Reg receptor system stimulates the PI(3)K/ATF‐2/cyclin D1 signaling pathway to induce β‐cell regeneration.

Lysine 129 of CD38 (ADP-ribosyl Cyclase/Cyclic ADP-ribose Hydrolase) Participates in the Binding of ATP to Inhibit the Cyclic ADP-ribose Hydrolase

CD38 catalyzes not only the formation of cyclic ADP-ribose (cADPR) from NAD+ but also the hydrolysis of cADPR to ADP-ribose (ADPR), and ATP inhibits the hydrolysis (Takasawa, S., Tohgo, A., Noguchi, N., Koguma, T., Nata, K., Sugimoto, T., Yonekura, H., and Okamoto, H. (1993) J. Biol. Chem. 268, 26052-26054). In the present study, using purified recombinant CD38, we showed that the cADPR hydrolase activity of CD38 was inhibited by ATP in a competitive manner with cADPR. To identify the binding site for ATP and/or cADPR, we labeled the purified CD38 with FSBA. Sequence analysis of the lysylendopeptidase-digested fragment of the labeled CD38 indicated that the FSBA-labeled residue was Lys-129. We introduced site-directed mutations to change the Lys-129 of CD38 to Ala and to Arg. Neither mutant was labeled with FSBA nor catalyzed the hydrolysis of cADPR to ADPR. Furthermore, the mutants did not bind cADPR, whereas they still used NAD+ as a substrate to form cADPR and ADPR. These results indicate that Lys-129 of CD38 participates in cADPR binding and that ATP competes with cADPR for the binding site, resulting in the inhibition of the cADPR hydrolase activity of CD38.

The CD38-cyclic ADP-ribose signalling system in insulin secretion: molecular basis and clinical implications.

In answer to the comments of Islam and Berggrenconcerning our hypothesis on the CD38-cyclic ADP-ribose (cADPR) signalling system, we will presentseveral lines of evidence that we believe can explainthe discrepancies between their view and ours.The Okamoto model and cADPRGlucose is the primary stimulus of insulin secretionand synthesis in pancreatic beta cells of the islets ofLangerhans [1–3]. Increases in the intracellular Ca

Important role of heparan sulfate in postnatal islet growth and insulin secretion.

Heparan sulfate (HS) binds with several signaling molecules and regulates ligand-receptor interactions, playing an essential role in embryonic development. Here we showed that HS was intensively expressed in pancreatic islet beta-cells after 1 week of age in mice. The enzymatic removal of HS in isolated islets resulted in attenuated glucose-induced insulin secretion with a concomitant reduction in gene expression of several key components in the insulin secretion machinery. We further depleted islet HS by inactivating the exostosin tumor-like 3 gene specifically in beta-cells. These mice exhibited abnormal islet morphology with reduced beta-cell proliferation after 1 week of age and glucose intolerance due to defective insulin secretion. These results demonstrate that islet HS is involved in the regulation of postnatal islet maturation and required to ensure normal insulin secretion.

Nucleotide sequence determination of chicken glucagon precursor cDNA: Chicken preproglucagon does not contain glucagon-like peptide II

cDNA clones coding for glucagon were isolated from a chicken pancreas cDNA library, and the nucleotide and amino acid sequences were determined. The amino acid sequence of chicken glucagon was HSQGTFTSDYSKYLDSRRAQDFVQWLMST, which was contained in the 151‐amino acid long precursor, being preceded by a signal sequence and an amino‐terminal peptide (NH2‐peptide) and followed by an intervening peptide and a glucagon‐like peptide I (GLP‐I). Chicken preproglucagon, however, lacked GLP‐II and intervening peptide II which have been shown to be contained in mammalian glucagon precursors.

Assignment of CD38, the gene encoding human leukocyte antigen CD38 (ADP-ribosyl cyclase/cyclic ADP-ribose hydrolase), to chromosome 4p15

CD38 has been used as a phenotype marker of lymphocyte differentiation. Recently, we have demonstrated that cyclic ADP-ribose can be synthesized and hydrolyzed by CD38 and acts as a second messenger in insulin secretion from pancreatic beta-cells. We have mapped the CD38 gene to human chromosome 4p15 by fluorescence in situ hybridization.