Epigenetics

Phosphoserine, the phosphorylated modification of the amino acid serine, is a central post-translational modification within a cell for many biological and biomedical processes. The phosphorylation of specifically four residue types - histidine, serine, threonine, and tyrosine occurs both within the cell as well as at the cell surface. This exquisitely controlled regulatory system controls a vast number of intertwined and interconnected downstream signaling pathways and cascades.

Over the past two decades, it has become clear that tyrosine phosphorylation plays a pivotal role in a variety of important signaling pathways in multicellular organisms. In the typical vertebrate cell, phosphotyrosine represents only a tiny fraction of total protein phosphorylation. Yet it is sufficient enough to induce malignant transformation (1), as unregulated phosphotyrosine signaling causes a breakdown in the normal regulation of cellular processes leading to several human diseases (2).

The polycomb group (PcG) protein, enhancer of zeste homolog 2 (EZH2) is a methyl-transferase that plays a key role in transcriptional gene repression. EZH2 is frequently overexpressed in several malignant tumors, and is often associated with advanced disease stage in many solid tumors.

Phosphotyrosine is the phosphorylated version of the amino acid tyrosine, which results from the activation of intracellular protein kinases (e.g. via growth factors) during normal growth and development, well as in transformation and oncogenesis. Phosphorylation of histidine, serine, threonine and tyrosine residues acts as a signaling system to control many cellular signaling pathways.

Enhancer of Zeste homolog 2 (EZH2) is the methyltransferase enzyme responsible for trimethylating lysine 27 on histone H3 to produce H3K27Me3. EZH2 is a polycomb group protein that is an essential epigenetic regulator that is often found deregulated in a wide variety of malignant cancer types.

Epigenetic mechanisms allow distinction between the active and inactive compartments of the genome, allowing proper cell lineage and embryogenesis.

Epigenetic alterations have come to prominence in biomedical research. In particular, hypermethylation of CpG islands located in the promoter regions of tumor-suppressor genes is now firmly established as an important mechanism for gene inactivation in cancer.

Discovery of histone variants using highly specific antibodies has led to the emerging notion that alterations in histone modifications and further changes in chromatin structure are induced by exchange of histone variants. Covalent histone modifications and the incorporation of histone variants bring about changes in chromatin structure that in turn alter the gene expression.

Histone modification is known to affect transcriptional access to chromatin. Therefore, high quality histone modification specific antibodies are necessary to understand and explain the specific roles that these epigenetic modifications play in transcription regulation. Unfortunately, many of the commercially available histone modification antibodies are designed against short immunizing peptides and lack specificity to the full-length modified histone.

DNA methyltransferases catalyze the transfer of the methyl group from S-andenosyl methionine (SAM) to DNA. Such methylation has wide ranging function in the cell, including organismal development and cell differentiation. In cancer, abnormal hypermethylation of gene promoter CpG islands can result in transcriptional silencing.