The Krüppel-Like Protein Gli-Similar 3 (Glis3) Functions as a Key Regulator of Insulin Transcription

Abstract

Transcriptional regulation of insulin in pancreatic β-cells is mediated primarily through enhancer elements located within the 5' upstream regulatory region of the preproinsulin gene. Recently, the Krüppel-like transcription factor, Gli-similar 3 (Glis3), was shown to bind the insulin (INS) promoter and positively influence insulin transcription. In this report, we examined in detail the synergistic activation of insulin transcription by Glis3 with coregulators, CREB-binding protein (CBP)/p300, pancreatic and duodenal homeobox 1 (Pdx1), neuronal differentiation 1 (NeuroD1), and v-maf musculoaponeurotic fibrosarcoma oncogene homolog A (MafA). Our data show that Glis3 expression, the binding of Glis3 to GlisBS, and its recruitment of CBP are required for optimal activation of the insulin promoter in pancreatic β-cells not only by Glis3, but also by Pdx1, MafA, and NeuroD1. Mutations in the GlisBS or small interfering RNA-directed knockdown of GLIS3 diminished insulin promoter activation by Pdx1, NeuroD1, and MafA, and neither Pdx1 nor MafA was able to stably associate with the insulin promoter when the GlisBS were mutated. In addition, a GlisBS mutation in the INS promoter implicated in the development of neonatal diabetes similarly abated activation by Pdx1, NeuroD1, and MafA that could be reversed by increased expression of exogenous Glis3. We therefore propose that recruitment of CBP/p300 by Glis3 provides a scaffold for the formation of a larger transcriptional regulatory complex that stabilizes the binding of Pdx1, NeuroD1, and MafA complexes to their respective binding sites within the insulin promoter. Taken together, these results indicate that Glis3 plays a pivotal role in the transcriptional regulation of insulin and may serve as an important therapeutic target for the treatment of diabetes.

Emerging roles of GLIS3 in neonatal diabetes, type 1 and type 2 diabetes

“…They further identified a GLIS3RE in the insulin gene promoter and found that GLIS3 physically and functionally interacts with PDX1, MAFA and NEUROD1 to control insulin gene transcription ). Subsequent study showed that mutations in the GLIS3RE markedly attenuated the insulin promoter activation by a combination of PDX1, MAFA and NEUROD1, indicating that the direct binding of GLIS3 to the insulin promoter is required for the interaction of its partners with the promoter (ZeRuth et al 2013). In agreement with these in vitro findings, Yang and coworkers found that tamoxifen-mediated β cell-specific inactivation of Glis3 in mice markedly downregulates insulin expression, leading to fulminant diabetes and death .…”

“…2). GLIS3 potently controls insulin gene transcription , ZeRuth et al 2013 as well as likely insulin secretion (Kang et al 2009b and β cell survival (Nogueira et al 2013, Dooley et al 2016, which perturbations may underlie all three forms of diabetes. Mutations or deletions in GLIS3 impair the proper expression and/or function of GLIS3 and its direct downstream target NGN3, causing severely abnormal β cell development in utero and marked impairment in insulin production at birth, culminating in permanent neonatal diabetes .…”

“…However, the underlying mechanisms were largely unknown until Glis3 global and β cell-specific knockout mice were generated. To gain insight into the role of GLIS3 in diabetes, three groups independently generated Glis3-deficient mice with different strategies (Kang et al 2009b, Watanabe et al 2009 and identified three direct downstream targets of GLIS3, such as NGN3 , insulin R80 Review x wen and y yang GLIS3 and diabetes 58 2 : R80 Review , ZeRuth et al 2013) and CCND2 , in the pancreatic progenitors and β cells. These studies reveal that GLIS3 is required not only for fetal islet differentiation but also for the maintenance of adult β cell function.…”

Transcription factor regulation of pancreatic organogenesis, differentiation and maturation

“…Glis3 has also been shown to regulate insulin expression in mature b-cells. 201,[203][204][205] Glis3 binding sites were located near the distal promoter region of Ngn3 and Glis3 also interacts with Hnf6. 206 The Glis3/Hnf6 protein complex may operate in conjunction with a larger transcription factor network to regulate Ngn3 expression and thus activate endocrine cell specification.…”

GLIS1–3 transcription factors: critical roles in the regulation of multiple physiological processes and diseases

“…Insulin ( Ins2 ), cyclin D2 ( Cdnd2 ), fibroblast growth factor 18 ( Fgf18 ), neurogenin 3 ( Ngn3 ), pendrin ( Pds ), and Na + /I - symporter ( Nis ) are among the genes directly regulated by GLIS3, while GLI1 , the Wnt family member 4 ( Wnt4 ) and Snail1 ( Snai1 ) are target genes of GLIS2 [17–22]. The interaction of GLIS proteins with GLISBS is mediated by their ZFD, which consists of a tandem repeat of five C2H2 zinc finger motifs [1, 5, 8, 16, 19]. All five zinc finger motifs are required for optimal binding of GLIS proteins to GLISBS; loss of the first zinc finger has the least impact on this interaction.…”