The Zinc Finger Protein ZBTB20 Regulates Transcription of Fructose-1,6-Bisphosphatase 1 and β Cell Function in Mice

BACKGROUND & AIMS: Fructose-1,6-bisphosphatase (FBP)-1 is a gluconeogenic enzyme that regulates glucose metabolism and insulin secretion in beta cells, but little is known about how its transcription is controlled. The zinc finger protein ZBTB20 regulates glucose homeostasis, so we investigated its effects on expression of FBP-1. METHODS: We analyzed gene expression using real-time reverse-transcription polymerase chain reaction, immunoblotting, and immunohistochemistry. We generated mice with beta cell-specific disruption of Zbtb20 using Cre/LoxP technology. Expression of Zbtb20 in beta cells was reduced using small interfering RNAs, and promoter occupancy and transcriptional regulation were analyzed by chromatin immunoprecipitation and reporter assays. RESULTS: ZBTB20 was expressed at high levels by beta cells and other endocrine cells in islets of normal mice; expression levels were reduced in islets from diabetic db/db mice. Mice with beta cell-specific knockout of Zbtb20 had normal development of beta cells but had hyperglycemia, hypoinsulinemia, glucose intolerance, and impaired glucose-stimulated insulin secretion. Islets isolated from these mice had impaired glucose metabolism, adenosine triphosphate production, and insulin secretion after glucose stimulation in vitro, although insulin secretion returned to normal levels in the presence of KCl. ZBTB20 knockdown with small interfering RNAs impaired glucose-stimulated insulin secretion in the beta cell line MIN6. Expression of Fbp1 was up-regulated in beta cells with ZBTB20 knockout or knockdown; impairments to glucose-stimulated insulin secretion were restored by inhibition of FBPase activity. ZBTB20 was recruited to the Fbp1 promoter and repressed its transcription in beta cells. CONCLUSIONS: The transcription factor ZBTB20 regulates beta cell function and glucose homeostasis in mice. It might be a therapeutic target for type 2 diabetes mellitus.