title: Identification of the ubiquitin-like domain of midnolin as a new glucokinase interaction partner.
abstract: Glucokinase acts as a glucose sensor in pancreatic beta cells. Its posttranslational regulation is important but not yet fully understood. Therefore, a pancreatic islet yeast two-hybrid library was produced and searched for glucokinase-binding proteins. A protein sequence containing a full-length ubiquitin-like domain was identified to interact with glucokinase. Mammalian two-hybrid and fluorescence resonance energy transfer analyses confirmed the interaction between glucokinase and the ubiquitin-like domain in insulin-secreting MIN6 cells and revealed the highest binding affinity at low glucose. Overexpression of parkin, an ubiquitin E3 ligase exhibiting an ubiquitin-like domain with high homology to the identified, diminished insulin secretion in MIN6 cells but had only some effect on glucokinase activity. Overexpression of the elucidated ubiquitin-like domain or midnolin, containing exactly this ubiquitin-like domain, significantly reduced both intrinsic glucokinase activity and glucose-induced insulin secretion. Midnolin has been to date classified as a nucleolar protein regulating mouse development. However, we could not confirm localization of midnolin in nucleoli. Fluorescence microscopy analyses revealed localization of midnolin in nucleus and cytoplasm and co-localization with glucokinase in pancreatic beta cells. In addition we could show that midnolin gene expression in pancreatic islets is up-regulated at low glucose and that the midnolin protein is highly expressed in pancreatic beta cells and also in liver, muscle, and brain of the adult mouse and cell lines of human and rat origin. Thus, the results of our study suggest that midnolin plays a role in cellular signaling of adult tissues and regulates glucokinase enzyme activity in pancreatic beta cells.
authors.affiliation: From the Institute of Clinical Biochemistry, Hannover Medical School, 30625 Hannover, Germany and.
authors.forename: Anke
authors.initials: A
authors.lastname: Hofmeister-Brix
authors.forename: Katrin
authors.initials: K
authors.lastname: Kollmann
authors.forename: Sara
authors.initials: S
authors.lastname: Langer
authors.forename: Julia
authors.initials: J
authors.lastname: Schultz
authors.forename: Sigurd
authors.initials: S
authors.lastname: Lenzen
authors.forename: Simone
authors.initials: S
authors.lastname: Baltrusch
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D005941:Glucokinase / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D006801:Humans; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000378:metabolism; D008297:Male; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000737:chemistry* / Q000378:metabolism*; D009928:Organ Specificity; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D025801:Ubiquitin / Q000737:chemistry*; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry / Q000378:metabolism
chemical_list: D007328:Insulin; D009687:Nuclear Proteins; D010446:Peptide Fragments; D025801:Ubiquitin; C414730:midnolin; D044767:Ubiquitin-Protein Ligases; C111567:parkin protein; D005941:Glucokinase; D005947:Glucose
keywords: Fluorescence Resonance Energy Transfer (FRET); Glucokinase; Insulin Secretion; Insulin Synthesis; Midnolin; Pancreatic Islets; Parkin; Two-hybrid System; Ubiquitin; Ubiquitin-like Domain