Oncohistones: A new tool to dissect the role of H4R3 methylation in chromatin biology
Lead Research Organisation:
University of Birmingham
Department Name: Institute of Cancer and Genomic Sciences
Abstract
Protein arginine methyltransferases (PRMTs) are enzymes that regulate the behaviour of proteins in the cell by adding a chemical methyl group to the amino acid arginine. This in turn regulates several important cellular processes and is significant for human health because PRMT levels are higher in cancer cells. This is important as it is now thought that cancer cells highjack PRMT functions and that this enables them to grow and evade chemotherapy treatments. Because of this, PRMTs are now priority drug targets for several global pharmaceutical companies, however, the precise mechanisms by which PRMTs contribute to cancer and therapy resistance are still largely unknown. Without this knowledge, successful translation of PRMT drugs into the clinic will be challenging.
One of the first proteins identified as methylated by PRMTs was a protein called histone H4. Histones enable the packaging of DNA into a structure called chromatin, and their chemical modification is important for gene expression and DNA repair. Whilst it has been appreciated that PRMTs regulate these cellular functions, there has been an inability to define the actual significance of histone H4 methylation because PRMTs also methylate other proteins that are involved in gene expression and DNA repair. This has thus led to a substantial knowledge gap in an important area of cancer biology.
Some cancers are driven by mutations in histones, so called "oncohistones". We have taken advantage of a newly identified cancer-associated oncohistone mutation that occurs at a site targeted by PRMTs, providing us with a clinically relevant tool to understand how PRMT-mediated methylation of histone H4 regulates gene expression and genome stability.
In this project, we will investigate in fine detail how this oncohistone regulates cancer cell behaviour and if it is a driver event in cancer development. We will use state-of-the-art techniques to determine if effects of oncohistone expression are due to deregulated PRMT methylation or the substitution of an arginine amino acid for another. We will determine mechanistically how the oncohistone affects gene expression and DNA repair, and if the recruitment of proteins to DNA is altered.
The impact of our study is far reaching, clinically important and timely because PRMT inhibitors are in phase I clinical trials for cancer treatment. It will enable us to define the importance of PRMT-dependent histone H4 methylation and explore how it regulates gene expression and genome stability, and how this contributes to cancer growth and chemoresistance. Crucially, it will provide insight into how PRMT inhibitors can be used in combination with agents that by modulating chromatin and/or DNA repair, thereby maximising their clinical potential and ultimately benefiting cancer patients.
One of the first proteins identified as methylated by PRMTs was a protein called histone H4. Histones enable the packaging of DNA into a structure called chromatin, and their chemical modification is important for gene expression and DNA repair. Whilst it has been appreciated that PRMTs regulate these cellular functions, there has been an inability to define the actual significance of histone H4 methylation because PRMTs also methylate other proteins that are involved in gene expression and DNA repair. This has thus led to a substantial knowledge gap in an important area of cancer biology.
Some cancers are driven by mutations in histones, so called "oncohistones". We have taken advantage of a newly identified cancer-associated oncohistone mutation that occurs at a site targeted by PRMTs, providing us with a clinically relevant tool to understand how PRMT-mediated methylation of histone H4 regulates gene expression and genome stability.
In this project, we will investigate in fine detail how this oncohistone regulates cancer cell behaviour and if it is a driver event in cancer development. We will use state-of-the-art techniques to determine if effects of oncohistone expression are due to deregulated PRMT methylation or the substitution of an arginine amino acid for another. We will determine mechanistically how the oncohistone affects gene expression and DNA repair, and if the recruitment of proteins to DNA is altered.
The impact of our study is far reaching, clinically important and timely because PRMT inhibitors are in phase I clinical trials for cancer treatment. It will enable us to define the importance of PRMT-dependent histone H4 methylation and explore how it regulates gene expression and genome stability, and how this contributes to cancer growth and chemoresistance. Crucially, it will provide insight into how PRMT inhibitors can be used in combination with agents that by modulating chromatin and/or DNA repair, thereby maximising their clinical potential and ultimately benefiting cancer patients.
Technical Summary
The consequences of cancer-associated mutations within histones, particularly at residues that undergo post-translational modification, has long been underestimated because histones are encoded for by multiple genes. It is therefore assumed that mutations in a single allele would be inconsequential on normal cellular function. Challenging this dogma, landmark studies on the H3K27M and H3K36M "oncohistones" have revealed several surprising discoveries. Oncohistones are thus a unique, clinically relevant biological tool for the study of the molecular basis of cancer because they enable a deeper understanding of fundamental cellular processes such as gene expression and genome stability that are deregulated during transformation.
Histone tails are also modified at arginine residues by the protein arginine methyltransferase (PRMT) family, enzymes that are overexpressed in cancer and are priority drug targets for several global pharmaceutical companies. Despite this, very little is understood about the genome-wide significance of histone arginine methylation, principally because PRMTs also methylate non-histone proteins such as transcription factors/cofactors, RNA splicing proteins and DNA repair proteins. Consequently, the use of PRMT inhibitors is unable to disentangle histone-dependent versus non-histone mechanisms for gene expression and genome.
To overcome this obstacle, we will use state-of-the-art methodologies and take advantage of a newly identified cancer-associated point mutation at a PRMT-targeted site presenting at histone H4 and will exploit this as a novel tool in which to dissect out the significance of Histone H4 methylation for gene expression, DNA repair and cellular transformation. Our data will provide crucial new insight that could reveal mechanisms of transformation and vulnerabilities that can be exploited with PRMT inhibitors.
Histone tails are also modified at arginine residues by the protein arginine methyltransferase (PRMT) family, enzymes that are overexpressed in cancer and are priority drug targets for several global pharmaceutical companies. Despite this, very little is understood about the genome-wide significance of histone arginine methylation, principally because PRMTs also methylate non-histone proteins such as transcription factors/cofactors, RNA splicing proteins and DNA repair proteins. Consequently, the use of PRMT inhibitors is unable to disentangle histone-dependent versus non-histone mechanisms for gene expression and genome.
To overcome this obstacle, we will use state-of-the-art methodologies and take advantage of a newly identified cancer-associated point mutation at a PRMT-targeted site presenting at histone H4 and will exploit this as a novel tool in which to dissect out the significance of Histone H4 methylation for gene expression, DNA repair and cellular transformation. Our data will provide crucial new insight that could reveal mechanisms of transformation and vulnerabilities that can be exploited with PRMT inhibitors.
