Krueppel-like transcription factor 11 (KLF11) inhibits activity of the human proinsulin promoter in pancreatic beta-cells

Abstract

KLF11 (TIEG2) is a member of the Sp1/KLF transcription factor family which plays an important role in mammalian gene regulation. KLF11 is a pancreas-enriched transcription factor that has elicited significant attention because of its role as negative regulator of exocrine cell growth in vitro and in vivo. However, its functional role in the endocrine pancreas remains to be established. Here we investigated endogenous expression of KLF11 in pancreatic beta-cells and analyzed the effects of KLF11 overexpression on human proinsulin promoter activity. RT-PCR revealed endogenous KLF11 mRNA expression in whole rat pancreas, human pancreatic islets and rat INS-1 beta-cells. Glucose stimulation does not seem to modulate KLF11 expression in INS-1 beta-cells. Transient co-transfection of human proinsulin promoter driven secreted alkaline phosphatase (SEAP) reporter gene vectors with KLF11 expression plasmids in INS-1 and betaTC3 beta-cells demonstrates dose-dependent, but glucose-independent KLF11-mediated repression of insulin promoter activity. 5((prime))-deletion analysis of the human proinsulin promoter sequence and gel-shift assays (EMSA) of protein/DNA binding indicate specific GC and CACCC boxes within the human proinsulin promoter as potential KLF11 binding sites. Further, KLF11 may interfere with SP1 binding sites at these response elements. In summary, we have identified Krueppel-like transcription factor 11 (KLF11) as a novel negative transcriptional regulator of human proinsulin gene expression in pancreatic beta-cells. Further we have characterized specific KLF11 DNA-response elements within the human proinsulin promoter. Impairment of KLF11-dependent transcriptional regulation of proinsulin expression may contribute to beta-cell dysfunction seen in the pathogenesis of diabetes mellitus.