Glucose Regulation of Insulin Gene Transcription and Pre-mRNA Processing in Human Islets

Abstract

Glucose is the primary regulator of insulin granule release from pancreatic islets. In rodent islets, the role of glucose in the acute regulation of insulin gene transcription has remained unclear, primarily because the abundance and long half-life of insulin mRNA confounds analysis of transcription by traditional methods that measure steady-state mRNA levels. To investigate the nature of glucose-regulated insulin gene transcription in human islets, we first quantitated the abundance and half-lives of insulin mRNA and pre-mRNAs after addition of actinomycin D (to stop transcription). Our results indicated that intron 1-and intron 2-containing pre-mRNAs were ϳ150-and 2,000-fold less abundant, respectively, than mature mRNA. 5 intron 2-containing pre-mRNAs displayed half-lives of only ϳ60 min, whereas all other transcripts displayed more extended lifetimes. In response to elevated glucose, pre-mRNA species increased within 60 min, whereas increases in mature mRNA did not occur until 48 h, suggesting that measurement of mature mRNA species does not accurately reflect the acute transcriptional response of the insulin gene to glucose. The acute increase in pre-mRNA species was preceded by a sixfold increase in histone H4 acetylation and a twofold increase in RNA polymerase II recruitment at the insulin promoter. Taken together, our data suggest that pre-mRNA species may be a more reliable reflection of acute changes to human insulin gene transcriptional rates and that glucose acutely enhances insulin transcription by a mechanism that enhances chromatin accessibility and leads to recruitment of basal transcriptional machinery.

A feat of metabolic proportions: Pdx1 orchestrates islet development and function in the maintenance of glucose homeostasis

“…This result may be secondary to the recruitment of the histone methyltransferase Set7/9 by Pdx1 [147]. Similarly, the glucose-stimulated increase in histone H4 acetylation (another marker of active, open chromatin) at the insulin gene in both cell lines and islets by Pdx1 is consistent with its recruitment of the histone acetyltransferase p300 [145,153,154]. These results suggest that an important component of gene activation by the Pdx1 protein complex may be its direct alteration of chromatin to a more open state, thereby permitting enhanced accessibility to other transcription factors and the basal transcriptional machinery.…”

The unique hypusine modification of eIF5A promotes islet β cell inflammation and dysfunction in mice

“…Five micrograms of total RNA from islets or INS-1 cells were reverse transcribed, as detailed previously (79). cDNA was subjected to quantitative PCR, using SYBR Green-based technology, and published primers for mouse Ins1/Ins2 pre-mRNA (80) and Quantitech primers (Qiagen) for all other mouse genes (81).…”

Novel splice variant of mouse insulin2 mRNA: Implications for insulin expression

“…Insulin, a pancreatic peptide hormone is regulated by glucose at various steps of insulin gene expression such as transcription, splicing, mRNA stability and translation [1][2][3][4]. The increase in insulin production within an hour of the glucose treatment occurs primarily due to increase in translation with no significant enhancement in mRNA levels [5].…”