Human NAA40 blocking peptide

Histone proteins are decorated with numerous post-(PTMs) or co-(CTMs) translational modifications mainly on their unstructured tails, but also on their globular domain. For many decades research on histone modifications has been focused almost solely on the biological role of modifications occurring at the side-chain of internal amino acid residues. In contrast, modifications on the terminal N-alpha amino group of histones-despite being highly abundant and evolutionarily conserved-have been largely overlooked. This oversight has been due to the fact that these marks were being considered inert until recently, serving no regulatory functions. However, during the past few years accumulating evidence has drawn attention towards the importance of chemical marks added at the very N-terminal tip of histones and unveiled their role in key biological processes including aging and carcinogenesis. Further elucidation of the molecular mechanisms through which these modifications are regulated and by which they act to influence chromatin dynamics and DNA-based processes like transcription is expected to enlighten our understanding of their emerging role in controlling cellular physiology and contribution to human disease. In this review, we clarify the difference between N-alpha terminal (Nt) and internal (In) histone modifications; provide an overview of the different types of known histone Nt-marks and the associated histone N-terminal transferases (NTTs); and explore how they function to shape gene expression, chromatin architecture and cellular phenotypes.

Protein N-terminal acetylation is an abundant post-translational modification in eukaryotes implicated in various fundamental cellular and biochemical processes. This modification is catalysed by evolutionarily conserved N-terminal acetyltransferases (NATs) whose deregulation has been linked to cancer development and thus, are emerging as useful diagnostic and therapeutic targets. Naa40 is a highly selective NAT that acetylates the aminotermini of histones H4 and H2A and acts as a sensor of cell growth in yeast. In the present study, we examine the role of Naa40 in cancer cell survival. We demonstrate that depletion of Naa40 in HCT116 and HT-29 colorectal cancer cells decreases cell survival by enhancing apoptosis, whereas Naa40 reduction in non-cancerous mouse embryonic fibroblasts has no effect on cell viability. Specifically, Naa40 knockdown in colon cancer cells activates the mitochondrial caspase-9-mediated apoptotic cascade. Consistent with this, we show that caspase-9 activation is required for the induced apoptosis because treatment of cells with an irreversible caspase-9 inhibitor impedes apoptosis when Naa40 is depleted. Furthermore, the effect of Naa40-depletion on cell-death is mediated through a p53-independent mechanism since p53-null HCT116 cells still undergo apoptosis upon reduction of the acetyltransferase. Altogether, these findings reveal an anti-apoptotic role for Naa40 and exhibit its potential as a therapeutic target in colorectal cancers.