title: A possible role of transglutaminase 2 in the nucleus of INS-1E and of cells of human pancreatic islets.
abstract: Transglutaminase 2 (TG2) is a multifunctional protein with Ca(2+)-dependent transamidating and G protein activity. Previously we reported that the role of TG2 in insulin secretion may involve cytoplasmic actin remodeling and a regulative action on other proteins during granule movement. The aim of this study was to gain a better insight into the role of TG2 transamidating activity in mitochondria and in the nucleus of INS-1E rat insulinoma cell line (INS-1E) during insulin secretion. To this end we labeled INS-1E with an artificial donor (biotinylated peptide), in basal condition and after stimulus with glucose for 2, 5, and 8min. Biotinylated proteins of the nuclear/mitochondrial-enriched fraction were analyzed using two-dimensional electrophoresis and mass spectrometry. Many mitochondrial proteins involved in Ca(2+) homeostasis (e.g. voltage-dependent anion-selective channel protein, prohibitin and different ATP synthase subunits) and many nuclear proteins involved in gene regulation (e.g. histone H3, barrier to autointegration factor and various heterogeneous nuclear ribonucleoprotein) were identified among a number of transamidating substrates of TG2 in INS-1E. The combined results provide evidence that a temporal link exists between glucose-stimulation, first phase insulin secretion and the action of TG on histone H3 both in INS-1E and human pancreatic islets.
  
  
  CONCLUSIONS
  Research into the role of transglutaminase 2 during insulin secretion in INS-1E rat insulinoma cellular model is depicting a complex role for this enzyme. Transglutaminase 2 acts in the different INS-1E compartments in the same way: catalyzing a post-translational modification event of its substrates. In this work we identify some mitochondrial and nuclear substrates of INS-1E during first phase insulin secretion. The finding that TG2 interacts with nuclear proteins that include BAF and histone H3 immediately after (2-5min) glucose stimulus of INS-1E suggests that TG2 may be involved not only in insulin secretion, as suggested by our previous studies in cytoplasmic INS-1E fraction, but also in the regulation of glucose-induced gene transcription.
authors.affiliation: Research Laboratories, Bambino Gesù Children's Hospital, IRCCS, Rome, Italy.
authors.forename: Sara
authors.initials: S
authors.lastname: Sileno
authors.affiliation: Confocal Microscopy Core Facility, Research Laboratory, Bambino Gesù Children's Hospital, IRCSS, Rome, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: D'Oria
authors.affiliation: Dulbecco Telethon Institute at IRCCS-Istituto di Ricerche Farmacologiche Mario Negri, Milano, Italy.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Stucchi
authors.affiliation: Proteome Biochemistry Unit, San Raffaele Scientific Institute, Milan, Italy.
authors.forename: Massimo
authors.initials: M
authors.lastname: Alessio
authors.affiliation: Confocal Microscopy Core Facility, Research Laboratory, Bambino Gesù Children's Hospital, IRCSS, Rome, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Petrini
authors.affiliation: Dulbecco Telethon Institute at IRCCS-Istituto di Ricerche Farmacologiche Mario Negri, Milano, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: Bonetto
authors.affiliation: Department of Cell Physiology and Metabolism, Geneva University Medical Centre, Geneva 4, Switzerland.
authors.forename: Pierre
authors.initials: P
authors.lastname: Maechler
authors.affiliation: Endocrinology Unit, Niguarda Hospital, Milan, Italy.
authors.forename: Federico
authors.initials: F
authors.lastname: Bertuzzi
authors.affiliation: Research Laboratories, Bambino Gesù Children's Hospital, IRCCS, Rome, Italy.
authors.forename: Valeria
authors.initials: V
authors.lastname: Grasso
authors.affiliation: Dulbecco Telethon Institute at IRCCS-Istituto di Ricerche Farmacologiche Mario Negri, Milano, Italy.
authors.forename: Katia
authors.initials: K
authors.lastname: Paolella
authors.affiliation: Research Laboratories, Bambino Gesù Children's Hospital, IRCCS, Rome, Italy; Department of Experimental Medicine and Surgery, University of Tor Vergata, Rome, Italy.
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Barbetti
authors.affiliation: Research Laboratories, Bambino Gesù Children's Hospital, IRCCS, Rome, Italy. Electronic address: o.massa@virgilio.it.
authors.forename: Ornella
authors.initials: O
authors.lastname: Massa
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000201:enzymology*; D019204:GTP-Binding Proteins; D005947:Glucose / Q000494:pharmacology; D006801:Humans; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000201:enzymology*; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D051381:Rats; D013549:Sweetening Agents / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology; D011503:Transglutaminases / Q000235:genetics / Q000378:metabolism*
chemical_list: D007328:Insulin; D013549:Sweetening Agents; C000717609:Tgm2 protein, rat; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D019204:GTP-Binding Proteins; D005947:Glucose; D002118:Calcium
keywords: Calcium concentration; FPIS; Human islet; INS-1E; Insulin secretion; TG2; Transglutaminase 2; first phase insulin secretion; transglutaminase 2.; β-Cell