Integrator of stress responses calmodulin binding transcription activator 1 (Camta1) Regulates miR-212/miR-132 Expression and insulin secretion

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Integrator of stress responses calmodulin binding transcription activator 1 (Camta1) Regulates miR-212/miR-132 Expression and insulin secretion. / Mollet, Inês Guerra Uerra; Malm, Helena Anna; Wendt, Anna; Orho-Melander, Marju; Eliasson, Lena.

In: Journal of Biological Chemistry, Vol. 291, No. 35, 26.08.2016, p. 18440-18452.

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T1 - Integrator of stress responses calmodulin binding transcription activator 1 (Camta1) Regulates miR-212/miR-132 Expression and insulin secretion

AU - Mollet, Inês Guerra Uerra

AU - Malm, Helena Anna

AU - Wendt, Anna

AU - Orho-Melander, Marju

AU - Eliasson, Lena

PY - 2016/8/26

Y1 - 2016/8/26

N2 - 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 Ca2+ 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.

AB - 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 Ca2+ 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.

KW - Insulin

KW - calmodulin binding

KW - bioinformatics

KW - rat

UR - http://www.scopus.com/inward/record.url?scp=84984706989&partnerID=8YFLogxK

U2 - 10.1074/jbc.M116.716860

DO - 10.1074/jbc.M116.716860

M3 - Article

VL - 291

SP - 18440

EP - 18452

JO - Journal of Biological Chemistry

JF - Journal of Biological Chemistry

SN - 1083-351X

IS - 35

ER -