Methyltransferase Set7/9 Maintains Transcription and Euchromatin Structure at Islet-Enriched Genes

Abstract

OBJECTIVE-The activation of ␤-cell genes, particularly of those encoding preproinsulin, requires an appropriate euchromatin (or "open") DNA template characterized by hypermethylation of Lys4 of histone H3. We hypothesized that this modification is maintained in islet ␤-cells by the action of the histone methyltransferase Set7/9. RESEARCH DESIGN AND METHODS-To identify the role of Set7/9, we characterized its expression pattern and gene regulation and studied its function using RNA interference in both cell lines and primary mouse islets.RESULTS-Within the pancreas, Set7/9 protein shows striking specificity for islet cells, including ␣-and ␤-cells, as well as occasional cells within ducts. Consistent with these findings, the Set7/9 gene promoter contained an islet-specific enhancer located between Ϫ5,768 and Ϫ6,030 base pairs (relative to the transcriptional start site) that exhibited Pdx1-responsive activation in ␤-cells. To study Set7/9 function, we depleted insulinoma cells and primary mouse islets of Set7/9 protein using siRNA. Following siRNA treatment, we observed striking repression of genes involved in glucose-stimulated insulin secretion, including Ins1/2, Glut2, and MafA. These changes in transcription were accompanied by loss of dimethylated H3 Lys4 and RNA polymerase II recruitment, particularly at the Ins1/2 and Glut2 genes. Consistent with these data, depletion of Set7/9 in islets led to defects in glucose-stimulated Ca 2ϩ mobilization and insulin secretion.CONCLUSIONS-We conclude that Set7/9 is required for normal ␤-cell function, likely through the maintenance of euchromatin structure at genes necessary for glucose-stimulated insulin secretion. Diabetes 58: [185][186][187][188][189][190][191][192][193] 2009

Transcriptional Activity of the Islet β Cell Factor Pdx1 Is Augmented by Lysine Methylation Catalyzed by the Methyltransferase Set7/9

“…Nevertheless, the full extent of the mechanisms governing Pdx1 action remains to be elucidated. Set7/9 is a Lys methyltransferase that has been shown to interact with Pdx1 and augment Pdx1 action at several target genes (26). In this study, we provide data suggesting that Set7/9-mediated methylation of Pdx1 augments Pdx1 transcriptional activity.…”

“…The CMV promoter-driven vector used to drive Setd7 has been described previously (25). Methods and primers for SYBR Green-based real-time RT-PCR have been described previously (26).…”

“…In prior studies, our group showed that transient knockdown of Set7/9 in islet ␤ cells results in a reduction in several gene targets of Pdx1 (26), but the link between Set7/9 and ␤ cell function in vivo has not been explored. To address this link more directly, we generated mice in which Cre recombinase recognition (Loxp) sites flanked exon 2 of the gene encoding Set7/9 (Setd7) so that conditional excision of the exon by Cre recombinase would result in a frameshift and premature termination of the mRNA (Fig.…”

Methyltransferase Set7/9 regulates p53 activity by interacting with Sirtuin 1 (SIRT1)

“…For example, Set7/9 interacts with Pdx1, an insulin transactivator, and catalyzes Pdx1 methylation. Although the interaction of Pdx1 with Set7/9 is able to recruit Set7/9 to histone H3 and induce H3K4 methylation (28,29), the methylation of Pdx1 is not directly associated with changes in Pdx1 function. In addition, although the methylation of DNMT1 leads to a decrease in the half-life of DNMT1, this modification is also not directly related to changes in DNMT1 methyltransferase activity (21,30).…”

Coordinate Changes in Histone Modifications, mRNA Levels, and Metabolite Profiles in Clonal INS-1 832/13 β-Cells Accompany Functional Adaptations to Lipotoxicity

“…Methylation of lysine residues 4, 36, and 79 of histone H3 are generally associated with active gene expression, whereas methylation of lysine residues 9 and 27 of histone H3 are associated with silenced or inactive chromatin (20,31). Set7/9, a H3 lysine 4 methyltransferase, has been found to regulate transcription of genes necessary for GSIS in ␤-cells (32,33).…”