Erin M. Bowers

Ghrelin is a gastric peptide hormone that stimulates weight gain in vertebrates. The biological activities of ghrelin require octanoylation of the peptide on Ser(3), an unusual posttranslational modification that is catalyzed by the enzyme ghrelin O-acyltransferase (GOAT). Here, we describe the design, synthesis, and characterization of GO-CoA-Tat, a peptide-based bisubstrate analog that antagonizes GOAT. GO-CoA-Tat potently inhibits GOAT in vitro, in cultured cells, and in mice. Intraperitoneal administration of GO-CoA-Tat improves glucose tolerance and reduces weight gain in wild-type mice but not in ghrelin-deficient mice, supporting the concept that its beneficial metabolic effects are due specifically to GOAT inhibition. In addition to serving as a research tool for mapping ghrelin actions, GO-CoA-Tat may help pave the way for clinical targeting of GOAT in metabolic diseases.

Histone modifications are reported to show different behaviors, associations, and functions in different genomic niches and organisms. We show here that rapid, continuous turnover of acetylation specifically targeted to all K4-trimethylated H3 tails (H3K4me3), but not to bulk histone H3 or H3 carrying other methylated lysines, is a common uniform characteristic of chromatin biology in higher eukaryotes, being precisely conserved in human, mouse, and Drosophila . Furthermore, dynamic acetylation targeted to H3K4me3 is mediated by the same lysine acetyltransferase, p300/cAMP response element binding (CREB)-binding protein (CBP), in both mouse and fly cells. RNA interference or chemical inhibition of p300/CBP using a newly discovered small molecule inhibitor, C646, blocks dynamic acetylation of H3K4me3 globally in mouse and fly cells, and locally across the promoter and start-site of inducible genes in the mouse, thereby disrupting RNA polymerase II association and the activation of these genes. Thus, rapid dynamic acetylation of all H3K4me3 mediated by p300/CBP is a general, evolutionarily conserved phenomenon playing an essential role in the induction of immediate-early (IE) genes. These studies indicate a more global function of p300/CBP in mediating rapid turnover of acetylation of all H3K4me3 across the nuclei of higher eukaryotes, rather than a tight promoter-restricted function targeted by complex formation with specific transcription factors.

Histone acetyltransferase enzymes (HATs) are important therapeutic targets, but there are few cell-based assays available for evaluating the pharmacodynamics of HAT inhibitors. Here we present the application of a FRET-based reporter, Histac, in live-cell studies of p300/CBP HAT inhibition, by both genetic and pharmacologic disruption. shRNA knockdown of p300/CBP led to increased Histac FRET, thus suggesting a role for p300/CBP in the acetylation of the histone H4 tail. Additionally, we describe a new p300/CBP HAT inhibitor, C107, and show that it can also increase cellular Histac FRET. Taken together, these studies provide a live-cell strategy for identifying and evaluating p300/CBP inhibitors.