Protocol for the genomic analysis of salt-fractionated chromatin from frozen murine liver.

Salt fractionation is a classical approach for separating chromatin based on its differential salt solubility and physical properties. Here, we present a protocol to apply salt fractionation for genome-scale profiling of chromatin isolated from livers at different stages of aging in mice. We elaborate on the steps to isolate nuclei, digest with micrococcal nuclease, sequentially salt fractionate, purify DNA, and construct libraries for genome profiling. We also include information on a computational pipeline for data analysis. For complete details on the use and execution of this protocol, please refer to Yang et al.1 This protocol is an adaptation of the salt fractionation method of Teves and Henikoff.2.

Unraveling the mechanism of centromere inactivation in human aging.

Aging involves a range of genetic, epigenetic, and physiological alterations. A key characteristic of aged cells is the loss of global heterochromatin, accompanied by a reduction in canonical histone levels. In this study, we track the fate of centromeres during aging in human cells. Our findings reveal that the centromeric histone H3 variant CENP-A is downregulated in aged cells, in a p53-dependent manner. We observe repression of centromeric noncoding transcription through an epigenetic mechanism via recruitment of a lysine-specific demethylase 1 (LSD1/KDM1A) to centromeres. This suppression results in defective de novo CENP-A loading at aging centromeres. By dual inhibition of p53 and LSD1/KDM1A in aged cells, we mitigate the reduction in centromeric proteins and centromeric transcripts, leading to mitotic rejuvenation of these cells. These results offer insights into a novel mechanism for centromeric inactivation during aging and provide potential strategies to reactivate centromeres.

Autophagy in Cancer: A Metabolic Perspective.

Autophagy is an intracellular catabolic degradative process in which damaged cellular organelles, unwanted proteins and different cytoplasmic components get recycled to maintain cellular homeostasis or metabolic balance. During autophagy, a double membrane vesicle is formed to engulf these cytosolic materials and fuse to lysosomes wherein the entire cargo degrades to be used again. Because of this unique recycling ability of cells, autophagy is a universal stress response mechanism. Dysregulation of autophagy leads to several diseases, including cancer, neurodegeneration and microbial infection. Thus, autophagy machineries have become targets for therapeutics. This chapter provides an overview of the paradoxical role of autophagy in tumorigenesis in the perspective of metabolism.

Breaking the aging epigenetic barrier.

Aging is an inexorable event occurring universally for all organisms characterized by the progressive loss of cell function. However, less is known about the key events occurring inside the nucleus in the process of aging. The advent of chromosome capture techniques and extensive modern sequencing technologies have illuminated a rather dynamic structure of chromatin inside the nucleus. As cells advance along their life cycle, chromatin condensation states alter which leads to a different epigenetic landscape, correlated with modified gene expression. The exact factors mediating these changes in the chromatin structure and function remain elusive in the context of aging cells. The accumulation of DNA damage, reactive oxygen species and loss of genomic integrity as cells cease to divide can contribute to a tumor stimulating environment. In this review, we focus on genomic and epigenomic changes occurring in an aged cell which can contribute to age-related tumor formation.

vp1524, a Vibrio parahaemolyticus NAD +-dependent deacetylase, regulates host response during infection by induction of host histone deacetylation.

Gram-negative intracellular pathogen Vibrio parahaemolyticus manifests its infection through a series of effector proteins released into the host via the type III secretion system. Most of these effector proteins alter signalling pathways of the host to facilitate survival and proliferation of bacteria inside host cells. Here, we report V. parahaemolyticus (serotype O3:K6) infection-induced histone deacetylation in host intestinal epithelial cells, particularly deacetylation of H3K9, H3K56, H3K18 and H4K16 residues. We found a putative NAD+-dependent deacetylase, vp1524 (vpCobB) of V. parahaemolyticus, was overexpressed during infection. Biochemical assays revealed that Vp1524 is a functional NAD+-dependent Sir2 family deacetylase in vitro, which was capable of deacetylating acetylated histones. Furthermore, we observed that vp1524 is expressed and localized to the nuclear periphery of the host cells during infection. Consequently, Vp1524 translocated to nuclear compartments of transfected cells, deacetylated histones, specifically causing deacetylation of those residues (K56, K16, K18) associated with V. parahaemolyticus infection. This infection induced deacetylation resulted in transcriptional repression of several host genes involved in epigenetic regulation, immune response, autophagy etc. Thus, our study shows that a V. parahaemolyticus lysine deacetylase Vp1524 is secreted inside the host cells during infection, modulating host gene expression through histone deacetylation.

Regulation of epigenetic state by non-histone chromatin proteins and transcription factors: Implications in disease.

Besides the fundamental components of the chromatin, DNA and octameric histone, the non-histone chromatin proteins and non-coding RNA play a critical role in the organization of functional chromatin domains. The non-histone chromatin proteins therefore regulate the transcriptional outcome in both physiological and pathophysiological state as well. They also help to maintain the epigenetic state of the genome indirectly. Several transcription factors and histone interacting factors also contribute in the maintenance of the epigenetic states, especially acetylation by the induction of autoacetylation ability of p300/CBP. Alterations of KAT activity have been found to be causally related to disease manifestation, and thus could be potential therapeutic target.

Chromatin protein PC4 is downregulated in breast cancer to promote disease progression: Implications of miR-29a.

The human transcriptional coactivator PC4 has numerous roles to play in the cell. Other than its transcriptional coactivation function, it facilitates chromatin organization, DNA damage repair, viral DNA replication, etc. Although it was found to be an essential protein in vivo, the importance of this multifunctional protein in the regulation of different cellular pathways has not been investigated in details, particularly in oncogenesis. In this study, PC4 downregulation was observed in a significant proportion of mammary tissues obtained from Breast cancer patient samples as well as in a subset of highly invasive and metastatic Breast cancer patient-derived cell lines. We have identified a miRNA, miR-29a which potentially reduce the expression of PC4 both in RNA and protein level. This miR-29a was found to be indeed overexpressed in a substantial number of Breast cancer patient samples and cell lines as well, suggesting one of the key mechanisms of PC4 downregulation. Stable Knockdown of PC4 in MCF7 cells induced its migratory as well as invasive properties. Furthermore, in an orthotopic breast cancer mice model system; we have shown that reduced expression of PC4 enhances the tumorigenic potential substantially. Absence of PC4 led to the upregulation of several genes involved in Epithelial to Mesenchymal Transition (EMT), indicating the possible mechanism of uniform tumour progression in the orthotropic mice. Collectively these data establish the role of PC4 in tumour suppression.

Nonhistone human chromatin protein PC4 is critical for genomic integrity and negatively regulates autophagy.

Multifunctional human transcriptional positive co-activator 4 (PC4) is a bona fide nonhistone component of the chromatin and plays a pivotal role in the process of chromatin compaction and functional genome organization. Knockdown of PC4 expression causes a drastic decompaction which leads to open conformation of the chromatin, and thereby altered nuclear architecture, defects in chromosome segregation and changed epigenetic landscape. Interestingly, these defects do not induce cellular death but result in enhanced cellular proliferation, possibly through enhanced autophagic activity. Moreover, PC4 depletion confers significant resistance to gamma irradiation. Exposure to gamma irradiation further induced autophagy in these cells. Inhibition of autophagy by small molecule inhibitors as well as by silencing of a critical autophagy gene drastically reduces the ability of PC4 knockdown cells to survive. On the contrary, complementation with wild-type PC4 could reverse this phenomenon, confirming the process of autophagy as the key mechanism for radiation resistance in the absence of PC4. These data connect the unexplored role of chromatin architecture in regulating autophagy during stress conditions such as radiation.

Multifunctional transcriptional coactivator PC4 is a global co-regulator of p53-dependent stress response and gene regulation.

Human positive coactivator 4 (PC4), a multifunctional chromatin-associated protein, is known to directly interact with p53 and modulate expressions of a few p53-dependent genes. However, the role of PC4 in p53's myriad of other regulatory functions is not known. The p53-PC4 interaction was selectively perturbed by a small peptide which led to abrogation of genotoxic stress-induced up-regulation of many p53-dependent genes and reduction of apoptosis in A549 cells. Over-expression of a PC4 point mutant, incapable of binding p53, recapitulated many of the effects of the peptide. Global gene expression profiling in A549 cells, upon peptide treatment, revealed PC4's involvement in the regulation of many p53-dependent pathways, including the Hippo pathway. Introduction of the peptide in neuronal cells significantly reduced its amyloid-ß-induced death. Thus, PC4 emerges as a global co-regulator of p53 and a therapeutic target against pathogeneses where the p53-dependent cell death process plays a crucial role.

Identification and characterization of nonhistone chromatin proteins: human positive coactivator 4 as a candidate.

The highly dynamic nucleoprotein structure of eukaryotic genome is organized in an ordered fashion, the unit of which is the nucleosome. The nucleosome is composed of core histones and DNA of variable size wrapped around it. Apart from the histone proteins, several nonhistone proteins also interact with the complex consisting of the DNA, the core and linker histones conferring highly regulated fluidity on the chromatin and permitting fine tuning of its functions. The nonhistone proteins are multifunctional and accentuate diverse cellular outcomes. In spite of the technical challenges, the architectural role of the nonhistone proteins altering the topology of the chromatin has been studied extensively. To appreciate the significance of the chromatin for genome function, it is essential to examine the role of the nonhistone proteins in different physiological conditions. Here, taking the example of a highly abundant chromatin protein, PC4 (Positive coactivator 4), we describe strategies for the identification of the chromatin-associated proteins and their structural and functional characterization.