Divya Reddy

Global histone post-translational modifications and cancer: Biomarkers for diagnosis, prognosis and treatment?

Global alterations in epigenetic landscape are now recognized as a hallmark of cancer. Epigenetic mechanisms such as DNA methylation, histone modifications, nucleosome positioning and non-coding RNAs are proven to have strong association with cancer. In particular, covalent post-translational modifications of histone proteins are known to play an important role in chromatin remodeling and thereby in regulation of gene expression. Further, histone modifications have also been associated with different aspects of carcinogenesis and have been studied for their role in the better management of cancer patients. In this review, we will explore and discuss how histone modifications are involved in cancer diagnosis, prognosis and treatment.

A novel method for isolation of histones from serum and its implications in therapeutics and prognosis of solid tumours

BackgroundDysregulation in post-translational modifications of histones and their modifiers are now well-recognized as a hallmark of cancer and can be used as biomarkers and potential therapeutic targets for disease progression and prognosis. In most solid tumours, a biopsy is challenging, costly, painful or potentially risky for the patient. Therefore, non-invasive methods like ‘liquid biopsy’ for analysis of histone modifications and their modifiers if possible will be helpful in the better clinical management of cancer patients.MethodsHere, we have developed a cost-effective and time-efficient protocol for isolation of circulating histones from serum of solid tumor, HCC, called Dual Acid Extraction (DAE) protocol and have confirmed by mass spectrometry. Also, we measured the activity of HDACs and HATs in serum samples.ResultsThe serum purified histones were profiled for changes in histone PTMs and have shown a comparable pattern of modifications like acetylation (H4K16Ac), methylation (H4K20Me3, H3K27Me3, H3K9Me3) and phosphorylation (γ-H2AX and H3S10P) to paired cancer tissues. Profiling for the histone PTM changes in various other organs of normal and tumor bearing animal suggests that the changes in the histone PTMs observed in the tumor serum is indeed due to changes in the tumor tissue only. Further, we demonstrate that the observed hypo-acetylation of histone H4 in tissue and serum samples of tumor bearing animals corroborated with the elevated HDAC activity in both samples compared to normal. Interestingly, human normal and tumor serum samples also showed elevated HDAC activity with no significant changes in HAT activity.ConclusionsOur study provides the first evidence in the context of histone PTMs and modifiers that liquid biopsy is a valuable predictive tool for monitoring disease progression. Importantly, with the advent of drugs that target specific enzymes involved in the epigenetic regulation of gene expression, liquid biopsy-based ‘real time’ monitoring will be useful for subgrouping of the patients for epi-drug treatment, predicting response to therapy, early relapse and prognosis.

Brief Communication: Featured Article: Histone H2A mono-ubiquitination and cellular transformation are inversely related in N-nitrosodiethylamine-induced hepatocellular carcinoma

Aberrant changes in histone post-translational modifications are encountered frequently in diseases like cancer. Although histone H3 post-translational modifications have been extensively studied in context of diseases, the functionally important histone H2A PTM H2A119ub (H2Aub) has not gained much attention. In this study, we report that H2Aub markedly decreases in hepatocellular carcinoma. Usp21, a H2A deubiquitinase, is probably responsible for decrease in H2Aub. In addition, the H2Aub levels showed an inverse correlation with H3S10 phosphorylation (H3S10p) and the proliferative state of the cells. Downregulation of H2Aub is also associated with increased expression of growth factor gene lipocalin 2. Interestingly, we show that treatment of cells with histone deacetylase inhibitor trichostatin A results in increase of H2Aub and decrease in H3S10p. Our work for the first time suggests the in vivo association of H3S10p, H4ac, and H2A119ub with cellular transformation.

MKP1 phosphatase mediates G1-specific dephosphorylation of H3Serine10P in response to DNA damage

Histone mark, H3S10 phosphorylation plays a dual role in a cell by maintaining relaxed chromatin for active transcription in interphase and condensed chromatin state in mitosis. The level of H3S10P has also been shown to alter on DNA damage; however, its cell cycle specific behavior and regulation during DNA damage response is largely unexplored. In the present study, we demonstrate G1 cell cycle phase specific reversible loss of H3S10P in response to IR-induced DNA damage is mediated by opposing activities of phosphatase, MKP1 and kinase, MSK1 of the MAP kinase pathway. We also show that the MKP1 recruits to the chromatin in response to DNA damage and correlates with the decrease of H3S10P, whereas MKP1 is released from chromatin during recovery phase of DDR. Furthermore, blocking of H3S10 dephosphorylation by MKP1 inhibition impairs DNA repair process and results in poor survival of WRL68 cells. Collectively, our data proposes a pathway regulating G1 cell cycle phase specific reversible reduction of H3S10P on IR induced DNA damage and also raises the possibility of combinatorial modulation of H3S10P with specific inhibitors to target the cancer cells in G1-phase of cell cycle.

Incorporation of a tag helps to overcome expression variability in a recombinant host

Highlights • Reason for the lack of recombinant protein expression in E. coli is indefinite.• Recombinant histone expression does not correlate with rare codon content.• Translational variability may lead to lack of expression or degradation of protein.• Expression variability could be averted by incorporating a tag.

Techniques to Access Histone Modifications and Variants in Cancer

Recent years have witnessed an explosion of epigenetic research on the role of histone variants and modifications in cancer. To understand the global dynamics of chromatin structure and function, analysis of histone variants incorporated into the nucleosome and their covalent modifications, is required. The nucleosome is the fundamental structural unit of chromatin, contains an octamer of core histones H3, H4, H2A, and H2B. The differential alterations in diverse histone variants and their accompanying modifications patterns will provide a deeper insight into their biological role in structural and functional properties of chromatin. Here we provide a step-by-step protocol to investigate these aspects, the histone modifications and variants, their localization and dynamics within specific regions of chromatin under distinct condition and the recruitment/retention of epigenetic regulators at their target sites in chromatin to influence cell growth and differentiation.