title: Integrator of Stress Responses Calmodulin Binding Transcription Activator 1 (Camta1) Regulates miR-212/miR-132 Expression and Insulin Secretion.
abstract: Altered microRNA profiles have been demonstrated in experimental models of type 2 diabetes, including in islets of the diabetic Goto-Kakizaki (GK) rat. Our bioinformatic analysis of conserved sequences in promoters of microRNAs, previously observed to be up-regulated in GK rat islets, revealed putative CGCG-core motifs on the promoter of the miR-212/miR-132 cluster, overexpression of which has been shown to increase insulin secretion. These motifs are possible targets of calmodulin binding transcription activators Camta1 and Camta2 that have been recognized as integrators of stress responses. We also identified putative NKE elements, possible targets of NK2 homeobox proteins like the essential islet transcription factor Nkx2-2. As Camtas can function as co-activators with NK2 proteins in other tissues, we explored the role of Camta1, Camta2, and Nkx2-2 in the regulation of the miR-212/miR-132 cluster and insulin secretion. We demonstrate that exposure of control Wistar or GK rat islets to 16.7 mm glucose increases miR-212/miR-132 expression but significantly less so in the GK rat. In addition, Camta1, Camta2, and Nkx2-2 were down-regulated in GK rat islets, and knockdown of Camta1 reduced miR-212/miR-132 promoter activity and miR-212/miR-132 expression, even under cAMP elevation. Knockdown of Camta1 decreased insulin secretion in INS-1 832/13 cells and Wistar rat islets but increased insulin content. Furthermore, knockdown of Camta1 reduced K(+)-induced insulin secretion and voltage-dependent Ca(2+) currents. We also demonstrate Camta1 and Nkx2-2 protein interaction. These results indicate that Camta1 is required not only for expression of the miR-212/miR-132 cluster but at multiple levels for regulating beta cell insulin content and secretion.
authors.affiliation: From the Department of Clinical Sciences, Clinical Research Centre, Lund University, Jan Waldenströms Gata 35, SE-20502 Malmö, Sweden inesmollet@gmail.com.
authors.forename: Inês Guerra
authors.identifier: 0000-0002-1422-1336
authors.initials: IG
authors.lastname: Mollet
authors.affiliation: From the Department of Clinical Sciences, Clinical Research Centre, Lund University, Jan Waldenströms Gata 35, SE-20502 Malmö, Sweden.
authors.forename: Helena Anna
authors.initials: HA
authors.lastname: Malm
authors.affiliation: From the Department of Clinical Sciences, Clinical Research Centre, Lund University, Jan Waldenströms Gata 35, SE-20502 Malmö, Sweden.
authors.forename: Anna
authors.identifier: 0000-0001-8807-5979
authors.initials: A
authors.lastname: Wendt
authors.affiliation: From the Department of Clinical Sciences, Clinical Research Centre, Lund University, Jan Waldenströms Gata 35, SE-20502 Malmö, Sweden.
authors.forename: Marju
authors.identifier: 0000-0002-3578-2503
authors.initials: M
authors.lastname: Orho-Melander
authors.affiliation: From the Department of Clinical Sciences, Clinical Research Centre, Lund University, Jan Waldenströms Gata 35, SE-20502 Malmö, Sweden.
authors.forename: Lena
authors.identifier: 0000-0002-6467-5029
authors.initials: L
authors.lastname: Eliasson
mesh_terms: D000818:Animals; D020013:Calcium Signaling; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D000090322:Homeobox Protein Nkx-2.2; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D007328:Insulin / Q000096:biosynthesis* / Q000235:genetics; D050417:Insulin-Secreting Cells / Q000378:metabolism*; D008297:Male; D051379:Mice; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins; D051381:Rats; D017208:Rats, Wistar; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D029961:Zebrafish Proteins
chemical_list: C487554:CAMTA1 protein, human; C000591996:CAMTA1 protein, mouse; D002135:Calcium-Binding Proteins; D000090322:Homeobox Protein Nkx-2.2; D018398:Homeodomain Proteins; D007328:Insulin; C547077:MIRN132 microRNA, human; C546976:MIRN132 microRNA, mouse; C548821:MIRN132 microRNA, rat; C551411:MIRN212 microRNA, human; C554518:MIRN212 microRNA, mouse; C552427:MIRN212 microRNA, rat; D035683:MicroRNAs; C000715631:NKX2-2 protein, human; C000715627:Nkx2-2 protein, mouse; C000715628:Nkx2-2 protein, rat; D009687:Nuclear Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D029961:Zebrafish Proteins; C000715630:nkx2.2b protein, zebrafish
keywords: NK2 homeobox 2 (Nkx2-2); beta cell (B-cell); calmodulin binding transcription activator 1 (Camta1); cyclic AMP (cAMP); insulin secretion; microRNA (miRNA); pancreatic islet; transcription coactivator; transcription promoter; type 2 diabetes