TSPYL2 Is Important for G1 Checkpoint Maintenance upon DNA Damage

Nucleosome assembly proteins play important roles in chromatin remodeling, which determines gene expression, cell proliferation and terminal differentiation. Testis specific protein, Y-encoded-like 2 (TSPYL2) is a nucleosome assembly protein expressed in neuronal precursors and mature neurons. Previous studies have shown that TSPYL2 binds cyclin B and inhibits cell proliferation in cultured cells suggesting a role in cell cycle regulation. To investigate the physiological significance of TSPYL2 in the control of cell cycle, we generated mice with targeted disruption of Tspyl2. These mutant mice appear grossly normal, have normal life span and do not exhibit increased tumor incidence. To define the role of TSPYL2 in DNA repair, checkpoint arrest and apoptosis, primary embryonic fibroblasts and thymocytes from Tspyl2 deficient mice were isolated and examined under unperturbed and stressed conditions. We show that mutant fibroblasts are impaired in G1 arrest under the situation of DNA damage induced by gamma irradiation. This is mainly attributed to the defective activation of p21 transcription despite proper p53 protein accumulation, suggesting that TSPYL2 is additionally required for p21 induction. TSPYL2 serves a biological role in maintaining the G1 checkpoint under stress condition

Interaction of the Transcription Start Site Core Region and Transcription Factor YY1 Determine Ascorbate Transporter SVCT2 Exon 1a Promoter Activity

Transcription of the ascorbate transporter, SVCT2, is driven by two distinct promoters in exon 1 of the transporter sequence. The exon 1a promoter lacks a classical transcription start site and little is known about regulation of promoter activity in the transcription start site core (TSSC) region. Here we present evidence that the TSSC binds the multifunctional initiator-binding protein YY1. Electrophoresis shift assays using YY1 antibody showed that YY1 is present as one of two major complexes that specifically bind to the TSSC. The other complex contains the transcription factor NF-Y. Mutations in the TSSC that decreased YY1 binding also impaired the exon 1a promoter activity despite the presence of an upstream activating NF-Y/USF complex, suggesting that YY1 is involved in the regulation of the exon 1a transcription. Furthermore, YY1 interaction with NF-Y and/or USF synergistically enhanced the exon 1a promoter activity in transient transfections and co-activator p300 enhanced their synergistic activation. We propose that the TSSC plays a vital role in the exon 1a transcription and that this function is partially carried out by the transcription factor YY1. Moreover, co-activator p300 might be able to synergistically enhance the TSSC function via a “bridge” mechanism with upstream sequences

Family Matters:Rethinking the Psychology of Human Social Motivation

What motives do people prioritize in their social lives? Historically, social psychologists, especially those adopting an evolutionary perspective, have devoted a great deal of research attention to sexual attraction and romantic-partner choice (mate seeking). Research on long-term familial bonds (mate retention and kin care) has been less thoroughly connected to relevant comparative and evolutionary work on other species, and in the case of kin care, these bonds have been less well researched. Examining varied sources of data from 27 societies around the world, we found that people generally view familial motives as primary in importance and mate-seeking motives as relatively low in importance. Compared with other groups, college students, single people, and men place relatively higher emphasis on mate seeking, but even those samples rated kin-care motives as more important. Furthermore, motives linked to long-term familial bonds are positively associated with psychological well-being, but mate-seeking motives are associated with anxiety and depression. We address theoretical and empirical reasons why there has been extensive research on mate seeking and why people prioritize goals related to long-term familial bonds over mating goals. Reallocating relatively greater research effort toward long-term familial relationships would likely yield many interesting new findings relevant to everyday people’s highest social priorities

Investigation of the Acetylation Mechanism by GCN5 Histone Acetyltransferase

The histone acetylation of post-translational modification can be highly dynamic and play a crucial role in regulating cellular proliferation, survival, differentiation and motility. Of the enzymes that mediate post-translation modifications, the GCN5 of the histone acetyltransferase (HAT) proteins family that add acetyl groups to target lysine residues within histones, has been most extensively studied. According to the mechanism studies of GCN5 related proteins, two key processes, deprotonation and acetylation, must be involved. However, as a fundamental issue, the structure of hGCN5/AcCoA/pH3 remains elusive. Although biological experiments have proved that GCN5 mediates the acetylation process through the sequential mechanism pathway, a dynamic view of the catalytic process and the molecular basis for hGCN5/AcCoA/pH3 are still not available and none of theoretical studies has been reported to other related enzymes in HAT family. To explore the molecular basis for the catalytic mechanism, computational approaches including molecular modeling, molecular dynamic (MD) simulation and quantum mechanics/molecular mechanics (QM/MM) simulation were carried out. The initial hGCN5/AcCoA/pH3 complex structure was modeled and a reasonable snapshot was extracted from the trajectory of a 20 ns MD simulation, with considering post-MD analysis and reported experimental results. Those residues playing crucial roles in binding affinity and acetylation reaction were comprehensively investigated. It demonstrated Glu80 acted as the general base for deprotonation of Lys171 from H3. Furthermore, the two-dimensional QM/MM potential energy surface was employed to study the sequential pathway acetylation mechanism. Energy barriers of addition-elimination reaction in acetylation obtained from QM/MM calculation indicated the point of the intermediate ternary complex. Our study may provide insights into the detailed mechanism for acetylation reaction of GCN5, and has important implications for the discovery of regulators against GCN5 enzymes and related HAT family enzymes

Lysine120 Interactions with p53 Response Elements can Allosterically Direct p53 Organization

p53 can serve as a paradigm in studies aiming to figure out how allosteric perturbations in transcription factors (TFs) triggered by small changes in DNA response element (RE) sequences, can spell selectivity in co-factor recruitment. p53-REs are 20-base pair (bp) DNA segments specifying diverse functions. They may be located near the transcription start sites or thousands of bps away in the genome. Their number has been estimated to be in the thousands, and they all share a common motif. A key question is then how does the p53 protein recognize a particular p53-RE sequence among all the similar ones? Here, representative p53-REs regulating diverse functions including cell cycle arrest, DNA repair, and apoptosis were simulated in explicit solvent. Among the major interactions between p53 and its REs involving Lys120, Arg280 and Arg248, the bps interacting with Lys120 vary while the interacting partners of other residues are less so. We observe that each p53-RE quarter site sequence has a unique pattern of interactions with p53 Lys120. The allosteric, DNA sequence-induced conformational and dynamic changes of the altered Lys120 interactions are amplified by the perturbation of other p53-DNA interactions. The combined subtle RE sequence-specific allosteric effects propagate in the p53 and in the DNA. The resulting amplified allosteric effects far away are reflected in changes in the overall p53 organization and in the p53 surface topology and residue fluctuations which play key roles in selective co-factor recruitment. As such, these observations suggest how similar p53-RE sequences can spell the preferred co-factor binding, which is the key to the selective gene transactivation and consequently different functional effects

Beta-HPV 5 and 8 E6 Promote p300 Degradation by Blocking AKT/p300 Association

The E6 oncoprotein from high-risk genus alpha human papillomaviruses (α-HPVs), such as HPV 16, has been well characterized with respect to the host-cell proteins it interacts with and corresponding signaling pathways that are disrupted due to these interactions. Less is known regarding the interacting partners of E6 from the genus beta papillomaviruses (β-HPVs); however, it is generally thought that β-HPV E6 proteins do not interact with many of the proteins known to bind to α-HPV E6. Here we identify p300 as a protein that interacts directly with E6 from both α- and β-HPV types. Importantly, this association appears much stronger with β-HPV types 5 and 8-E6 than with α-HPV type 16-E6 or β-HPV type 38-E6. We demonstrate that the enhanced association between 5/8-E6 and p300 leads to p300 degradation in a proteasomal-dependent but E6AP-independent manner. Rather, 5/8-E6 inhibit the association of AKT with p300, an event necessary to ensure p300 stability within the cell. Finally, we demonstrate that the decreased p300 protein levels concomitantly affect downstream signaling events, such as the expression of differentiation markers K1, K10 and Involucrin. Together, these results demonstrate a unique way in which β-HPV E6 proteins are able to affect host-cell signaling in a manner distinct from that of the α-HPVs

Human EHMT2/G9a activates p53 through methylation-independent mechanism

p53 is a critical tumor suppressor in humans. It functions mostly as a transcriptional factor and its activity is regulated by numerous post-translational modifications. Among different covalent modifications found on p53 the most controversial one is lysine methylation. We found that human G9a (hG9a) unlike its mouse orthologue (mG9a) potently stimulated p53 transcriptional activity. Both ectopic and endogenous hG9a augmented p53-dependent transcription of pro-apoptotic genes, including Bax and Puma, resulting in enhanced apoptosis and reduced colony formation. Significantly, shRNA-mediated knockdown of hG9a attenuated p53-dependent activation of Puma. On the molecular level, hG9a interacted with histone acetyltransferase, p300/CBP, resulting in increased histone acetylation at the promoter of Puma. The bioinformatics data substantiated our findings showing that positive correlation between G9a and p53 expression is associated with better survival of lung cancer patients. Collectively, this study demonstrates that depending on the cellular and organismal context, orthologous proteins may exert both overlapping and opposing functions. Furthermore, this finding has important ramifications on the use of G9a inhibitors in combination with genotoxic drugs to treat p53-positive tumors.Oncogene advance online publication, 25 July 2016; doi:10.1038/onc.2016.258

The microRNA and p53 families join forces against cancer

The product of the TP53 gene, p53, is one of the most recognised and extensively studied molecules that protects multicellular organisms from cancer. The well-deserved fame of p53 stems from the nature of its function – to coordinate an appropriate cellular response to various forms of genotoxic stress through cell cycle arrest, senescence and/or apoptosis. Given the importance of this role, it is not, perhaps, surprising that p53 was found to be inactive in more than half of human cancers. It should be noted that p53 does not work alone but cooperates with two ancestral proteins of the same family, p63 and p73. Aiming to broaden our understanding of the function of the p53 family of proteins in cancer, the mini-symposium held in the University of Leicester provided an opportunity for scientists and clinicians to exchange knowledge and expertise and to establish new collaborations. The main focus of this event was on the recently emerged link between the p53 family members and microRNA during cancer development

Lysine-specific post-translational modifications of proteins in the life cycle of viruses

The process of protein post-translational modifications (PTM) is one of the critical mechanisms of regulation of many cellular processes, which makes it an attractive target for various viruses. Since viruses cannot replicate on their own, they have developed unique abilities to alter metabolic and signaling cell pathways, including protein PTMs, to ensure faithful replication of their genomes. This review describes several ways of how lysine-specific PTMs are used by various viruses to ensure its successful invasion and replication. Covalent modifications like acetylation, ubiquitination, and methylation form a complex system of reversible and often competing modifications, which adds an additional level of complexity to the system of regulation of the activity of host proteins involved in viral replication and propagation. In furthering these, we also describe the manner in which PTM pathways can also be accosted by various types of viruses to neutralize the host's cellular mechanisms for anti-viral protection and highlight key areas for future therapeutic targeting and design

AMP-activated protein kinase: Structure, function, and role in pathological processes

Recently, AMP-activated protein kinase (AMPK) has emerged as a key regulator of energy balance at cellular and whole-body levels. Due to the involvement in multiple signaling pathways, AMPK efficiently controls ATP-consuming/ATP-generating processes to maintain energy homeostasis under stress conditions. Loss of the kinase activity or attenuation of its expression leads to a variety of metabolic disorders and increases cancer risk. In this review, we discuss recent findings on the structure of AMPK, its activation mechanisms, as well as the consequences of its targets in regulation of metabolism. Particular attention is given to low-molecular-weight compounds that activate or inhibit AMPK; the perspective of therapeutic use of such modulators in treatment of several common diseases is discussed