We showed earlier that p300/CBP plays an important role in G1 progression by negatively regulating c-Myc and thereby preventing premature G1 exit. Here, we have studied the mechanism by which p300 represses c-Myc and show that in quiescent cells p300 cooperates with histone deacetylase 3 (HDAC3) to repress transcription. p300 and HDAC3 are recruited to the upstream YY1-binding site of the c-Myc promoter resulting in chromatin deacetylation and repression of c-Myc transcription. Consistent with this, ablation of p300, YY1 or HDAC3 expression results in chromatin acetylation and induction of c-Myc. These three proteins exist as a complex in vivo and form a multiprotein complex with the YY1-binding site in vitro. The C-terminal region of p300 is both necessary and sufficient for the repression of c-Myc. These and other results suggest that in quiescent cells the C-terminal region of p300 provides corepressor function and facilitates the recruitment of p300 and HDAC3 to the YY1-binding site and represses the c-Myc promoter. This corepressor function of p300 prevents the inappropriate induction of c-Myc and S phase.

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Epigenetic therapies, including DNA methyltransferase and histone deacetylase (HDAC) inhibitors, are increasingly being considered to treat hematological malignancies, but their effects on normal hematopoietic stem cells (HSCs) remain largely unexplored. We compared the effects of several HDAC inhibitors, including valproic acid (VPA) and trichostatin A (TSA), alone or in combination with 5-aza-2'-deoxycytidine (5azaD) on the expansion of HSCs. VPA induced the highest expansion of CD34+CD90+ cells and progenitor cells compared with other HDAC inhibitors or the sequential addition of 5azaD/TSA in culture. Xenotransplantation studies demonstrated that VPA prevents HSC loss, whereas 5azaD/TSA treatment leads to a net expansion of HSCs that retain serial transplantation ability. 5azaD/TSA-mediated HSC expansion was associated with increased histone acetylation and transient DNA demethylation, which corresponded with higher gene transcript levels. However, some genes with increased transcript levels lacked changes in methylation. Importantly, a global microarray analysis revealed a set of differentially expressed genes in 5azaD/TSA- and VPA-expanded CD34+ cells that might be involved in the expansion and maintenance of transplantable HSCs, respectively. In summary, our data indicate that treatment of HSCs with different chromatin-modifying agents results in either the expansion or maintenance of HSCs, an observation of potential therapeutic importance.

Our previous report on multiwall carbon nanotubes (MWCNT) has demonstrated the generation of reactive radicals and depletion of intracellular antioxidants which in turn cause cell death through activation of caspases. The molecular mechanism of cellular death due to MWCNT is not clear yet. In this study, we investigated the signaling pathways implicated in MWCNT-induced apoptosis in rat lung epithelial cells. First, we assessed the DNA damage in response to MWCNT treatment and showed the significant DNA damage as compared to control. The collapse of the mitochondrial membrane integrity, release of cytochrome c into the cytosol, reduction in cellular ATP content, increased levels of mitochondrial apoptogenic factor and activation and nuclear translocation of NF-κB were observed in MWCNT treated cells. In addition, a time-dependent induction of phosphorylated IκBα and its degradation were detected in cells exposed to MWCNT. Furthermore, MWCNT activated several death related proteins including apoptosis inducing factor, p53, p21 and bax. Together, our results suggest that signaling pathways such as NF-κB and AP-1 are activated upon MWCNT treatment for cellular cytotoxicity.

We recently reported that the transcriptional coactivator and histone acetyltransferase p300 plays an important role in the G 1 phase of the cell cycle by negatively regulating c-myc and thereby preventing premature G 1 exit (Kolli, et al. Here, we show that antisense-mediated depletion of CBP in serum-deprived human cells leads to induction of c-myc and that such cells emerge from quiescence without growth factors at a rate comparable with that of p300-depleted cells. The CBP-depleted cells contained significantly reduced levels of the cyclin-dependent kinase inhibitor p21 and low levels of p107 and p130 (but not pRb) phosphorylation, suggesting that these factors, along with elevated levels of c-Myc, contribute to induction of DNA synthesis. Antisense c-Myc reversed the phosphorylation of p107 and p130 and the induction of S phase in CBP-depleted cells, indicating that up-regulation of c-myc is directly responsible for the induction of S phase. Furthermore, the serum-stimulated p300/CBP-depleted cells did not traverse beyond S phase, and a significant number of these cells died of apoptosis, which was not related to p53 levels. These cells also contained significantly higher levels of c-Myc compared with normal cells. When c-myc expression was blocked by antisense cMyc, the apoptosis of the serum-stimulated CBPdepleted cells was reversed, indicating that high levels of c-Myc contribute to apoptosis. Thus, despite their high degree of structural and functional similarities, normal levels of both p300 and CBP are essential for keeping c-myc in a repressed state in G 1 and thereby preventing inappropriate entry of cells into S phase. In addition, both these proteins also provide important functions in coordinated cell cycle progression. p300 and the CBP 1 are two large highly homologous and conserved transcriptional adapter proteins containing histone acetyltransferase activity that link transcription with chroma-

Nanoparticles are increasingly being recognized for their potential utility in biological applications including nanomedicine. Here, we have synthesized zinc oxide (ZnO) nanorods using zinc acetate and hexamethylenetetramine as precursors followed by characterizing using X-ray diffraction, fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. The growth of synthesized zinc oxide nanorods was found to be very close to its hexagonal nature, which is confirmed by X-ray diffraction. The nanorod was grown perpendicular to the long-axis and grew along the [001] direction, which is the nature of ZnO growth. The morphology of synthesized ZnO nanorods from the individual crystalline nucleus was confirmed by scanning and transmission electron microscopy. The length of the nanorod was estimated to be around 21 nm in diameter and 50 nm in length. Our toxicology studies showed that synthesized ZnO nanorods exposure on hela cells has no significant induction of oxidative stress or cell death even in higher concentration (10 μg/ml). The results suggest that ZnO nanorods might be a safer nanomaterial for biological applications.Keywords: Zinc oxide [ZnO]; Nanorods; XRD; SEM & TEM; Cytotoxicity Citation: R. Gopikrishnan, K. Zhang, P. Ravichandran, S. Baluchamy, V. Ramesh, S. Biradar, P. Ramesh, J. Pradhan, J. C. Hall, A. K. Pradhan and G. T. Ramesh, "Synthesis, characterization and biocompatibility studies of zinc oxide (ZnO) nanorods for biomedical application", Nano-Micro Lett. 2, 31-36 (2010). doi: 10.5101/nml.v2i1.p31-36 Nanotechnology has extraordinary potential to change our lives by improving existing products and enabling new ones. It facilitates the development of new materials in the 1a100 nm range, comparable to the size range of biological molecules and structures [1]. Nanomaterials are very attractive materials for the manipulation, sensing and detection of biological structures and systems [2]. The principal factors which make nanomaterials different from their bulk counterparts include an increase in their relative surface area and quantum effects, which affect their physical and chemical properties [2]. This is due to the large surface area-to-volume ratio of nanoparticles, which increases surface free energy to a point that is comparable to their lattice energy. For example, a particle of 30 nm size has 5% of its atoms on its surface compared to 50% of the atoms on the surface of a 3 nm particle [3]. The altered properties of nanomaterials, and their size similarity to naturally occurring cell structures, will allow them to interact readily with bio molecules and potentially affect the cellular responses in a dynamic and selective manner. Materials that exploit these characteristics are becoming increasingly attractive for use in novel biomedical applications.Nano structured materials exhibit unique properties related to their size, and are used in an array of applications such as optoelectronics, nano/microelectronics, sensors, transducers, cosmetics as w...

The synthesis of nanoparticles and their functionalization to effectively utilize them in biological applications including drug delivery is currently a challenge. Calcium carbonate among many other inorganic nanosized particles offers promising results for such applications. We have synthesized calcium carbonate nanoparticles using polymer mediated growth technique, where one of the ions bound within polymer matrix and the other diffuses and reacts to form desired compound. The synthesized nanoparticles are characterized using X-ray diffraction, Scanning Electron Microscopy and spectroscopic techniques such as Fourier-Transform Infra-red spectroscopy and UV-Vis spectroscopy. The diameter of the calcium carbonate nanoparticles is estimated to be 39.8 nm and their biocompatibility studies showed no significant induction of oxidative stress or cell death even at higher concentrations (50 microg) upon exposure to HeLa and LE cells. Here, we report that the synthesized calcium carbonate nanosized particles using polymer mediated growth technique are biocompatible and can be safely used for biomedical applications.