Another great Keystone event kicked off the spring conference season and the University of Nebraska Medical Center’s Catherine Murari-Kanti was there to soak it all in. Check out her coverage to see what happened:
This symposia, held in Santa Fe, attracted mostly academic stalwarts in the field of epigenetics along with a few representatives from pharmaceutical companies such as GlaxoSmithKline, Celgene Corp. etc. The convention center located in downtown Santa Fe, allowed for two groups of the Keystone Symposia to have their meeting there at the same time. The Q1 session was the Cancer Epigenetics Meeting while Q2 was the Transcriptional Regulation meeting. The combined sessions held about 500 people present in the main conference room. Later in the evenings, Poster Sessions were arranged in an adjacent conference room, complete with an open bar and plenty of hors d’oeuvres for each of the three days. I found the following talks very interesting to me because of their content as well as how they were presented:
Chemical Modulation of Chromatin Structure and Function
James E. Bradner, Dana-Farber Cancer Institute
Going with the theme of being in New Mexico, James started his talk with an opening slide of the typical smoke-filled green colored letters from Breaking Bad, but his title-slide read, Breaking Bromodomain and extra terminal BETs. Dr. Bradner started by explaining how cancer is a disease of super enhancers and how readers of epigenetic marks are evolutionarily conserved and recognize modifications made to lysine tails of histones.
The Bradner lab focuses on BRD4, which is a member of the BET family and is critical to transcriptional elongation and is involved in the recruitment of positive transcription elongation factor complex (P-TEFb). BRD4 is an important component in the recurrent t(15;19) chromosomal translocation found in the aggressive form of human squamous carcinoma. Cell lines with the BRD4-NUT (nuclear protein in testis) oncoprotein have a proliferation advantage and differentiation block. The Bradner lab was able to develop, JQ1 which inhibits BRD4 by binding to Kac binding site of BRD4 of the BRD4-NUT oncoprotein and elegantly proved by a variety of experiments. This inhibition was then proved to be able to induce differentiation and growth arrest. JQ1’s anti-tumor effects were also proved in xenograft samples. JQ1 was one of its kind in the BET family inhibitors.
After Dr. Bradner discussed his science he discussed how he wanted science to be more of a collaborative industry than a “me-and-mine” kind of research. Bradner mentioned how he was willing to give 1gm of his newly founded drug for free, without any need for acknowledgements or authorship. However there were still a few people out there who were actually buying the drug from various companies and he tried very hard to state that the more collaborative science is, the better it is for future generations. Bradner’s talk was very well received considering his new faculty position and that his lab has only been established for three years.
Cellular Metabolism and Epigenetic Changes in Cancer
Craig B. Thompson, Memorial Sloan-Kettering Cancer Center
To throw light on the interesting topic, Dr. Thompson spent quite a bit of time on the role of metabolism in epigenetics in general. Histone acetyltransferases (HATs) transfer the acetyl group of the acetyl coA to the lysine residues of histones and produce coA as the end product making acetyl coA made from the body’s metabolism, a major metabolic unit into histone acetylation. Histone deacetylation is regulated by caloric restriction because in the presence of low nutrition, there is a decrease in Sirt1 levels. Histone Methylation usually causes silencing of genes which is a very energy requiring process. However tumor cells still prefer to use histone methylation to bring about silencing of many tumor suppressor genes. The extent to which a cell can engage in acetylation or deacetylation or methylation is dependent on the cell to utilize glucose.
Thompson then took the example of metabolic enzyme isocitrate dehydrogenase 1 (IDH1) that transfers NADPH to the cytosol. IDH1 interconverts isocitrate and α-ketoglutarate (α-KG) in the cytosol and mitochondria respectively. IDH1 is frequently mutated in various gliomas, adult de novo acute myeloid leukemias (AMLs) causing a loss of function, missense, error in the active site which occurs exclusively in the amino acids required for the binding to isocitrate. Mutant IDH1 causes the conversion of α-KG to 2-hydroxyglutarate (2-HG) and high levels of this new metabolite is usually found as high as 100-fold in AML patients. TET2 mutations were found in patient samples with mutually exclusive IDH mutations and this loss of function of TET2 mutations along with the IDH mutation blocked then TET2- induced increase in 5-hydroxymethylcytosine. Thompson also discussed how the combined effect of the accumulation of 2-HG and loss of TET2 leads to the block of a common myeloid progenitor. Thompson mentioned the drug AGI-6780 which potently and selectively inhibits tumor related IDH1/2. All of this pointed to how cellular metabolism plays such an important role in the regulation of epigenetic regulators.
CpG Island Methylation in Cancer: What is the trigger?
Susan J. Clark, Garvan Institute of Medical Research
I loved this talk because I believe Dr. Clark did an excellent job of showing the step by step process of how they learned what triggers hypermethylation of tumor suppressor genes in cancer cells. For this purpose Clark studied the CpG island-associated with the Glutathione S-transferase (GSTP1) gene which is hypermethylated in prostate tumors but is completely unmethylated in normal prostate cells.
The first question they asked was if there was something about the GSTP1 gene sequence itself that makes it susceptible to hypermethylation, to confirm this, they transfected normal GSTP1 gene sequence into LNCaP cells but the gene sequence remained unmethylated even after 22 passages. They then wanted to test if active transcription would protect the CpG sites from hypermethylation but it was not so. They also found that if the boundary elements around the CpG islands were removed or if the gene was silenced earlier that it did not affect hypermethylation. They then proposed the “Seeding and silencing: trigger for hypermethylation” model wherein they suggested that 2 events have to happen in combination which includes the inactivation of a particular gene and random “seeds” of methylation in CpG island which eventually would act as a trigger for further de novo methylation. This low level of methylation that is observed in an invactivated gene (through an oncogenic, independent process) is enough to promote hypermethylation and allow for the binding of methylation binding proteins such as MBD2.
Clark’s lab confirmed through a series of experiments that it was MBD2 and not McCP2 that were associated with the silenced promoter. They found that in cancer cells, MBD2 can bind to low level methylated cells (seeds) and with the help of DNMTs and HDACs, can play a role in de novo methylation. She went on to prove that MBD2 is not just a reader of methylation but plays a critical role in defining the specificity of DNA hypermethylation.
**EpiGenie would like to send a big “Thanks!” to Catherine Murari-Kanti who is a PhD candidate in the laboratory of Michael G. Brattain (PhD) in the Eppley Department of University of Nebraska Medical Center, for providing this conference report.**