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ABSTRACT: DNA decatenation mediated by Topoisomerase II is required to separate the interlinked sister chromatids post-replication. SGS1, a yeast homolog of the human RecQ family of helicases interacts with Topoisomerase II and plays a role in chromosome segregation, but this functional interaction has yet to be identified in higher organisms. Here, we report a physical and functional interaction of Topoisomerase IIα with RECQL5, one of five mammalian RecQ helicases, during DNA replication. Direct interaction of RECQL5 with Topoisomerase IIα stimulates the decatenation activity of Topoisomerase IIα. Consistent with these observations, RECQL5 co-localizes with Topoisomerase IIα during S-phase of the cell cycle. Moreover, cells with stable depletions of RECQL5 display a slow proliferation rate, a G2/M cell cycle arrest and late S-phase cycling defects. Metaphase spreads generated from RECQL5-depleted cells exhibit undercondensed and entangled chromosomes. Further, RECQL5-depleted cells activate a G2/M checkpoint and undergo apoptosis. These phenotypes are similar to those observed when Topoisomerase II catalytic activity is inhibited. These results reveal an important role for RECQL5 in the maintenance of genomic stability and a new insight into the decatenation process.
Nucleic Acids Research 02/2012; 40(4):1621-35. · 8.03 Impact Factor
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ABSTRACT: To understand the mechanism regulating the effector function of memory CD8 T cells, we examined expression and chromatin state of a key transcription factor (eomesodermin, EOMES) and two of its targets: perforin (PRF1) and granzyme B (GZMB). Accessible chromatin associated histone 3 lysine 9 acetylation (H3K9Ac) was found significantly higher at the proximal promoter and the first exon region of all three genes in memory CD8 T cells than in naive CD8 T cells. Correspondingly, EOMES and PRF1 were constitutively higher expressed in memory CD8 T cells than in naive CD8 T cells at resting and activated states. In contrast, higher expression of GZMB was induced in memory CD8 T cells than in naive CD8 T cells only after activation. Regardless of their constitutive or inducible expression, decreased H3K9Ac levels after treatment with a histone acetyltransferase inhibitor (Curcumin) led to decreased expression of all three genes in activated memory CD8 T cells. These findings suggest that H3K9Ac associated accessible chromatin state serves as a corner stone for the differentially high expression of these effector genes in memory CD8 T cells. Thus, epigenetic changes mediated via histone acetylation may provide a chromatin "memory" for the rapid and robust transcriptional response of memory CD8 T cells.
The Journal of Immunology 06/2008; 180(12):8102-8. · 5.79 Impact Factor
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Monchou Fann,
Jason M Godlove,
Marta Catalfamo,
William H Wood,
Francis J Chrest,
Nicholas Chun,
Larry Granger, Robert Wersto,
Karen Madara,
Kevin Becker,
Pierre A Henkart,
Nan-Ping Weng
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ABSTRACT: To understand the molecular basis for the rapid and robust memory T-cell responses, we examined gene expression and chromatin modification by histone H3 lysine 9 (H3K9) acetylation in resting and activated human naive and memory CD8(+) T cells. We found that, although overall gene expression patterns were similar, a number of genes are differentially expressed in either memory or naive cells in their resting and activated states. To further elucidate the basis for differential gene expression, we assessed the role of histone H3K9 acetylation in differential gene expression. Strikingly, higher H3K9 acetylation levels were detected in resting memory cells, prior to their activation, for those genes that were differentially expressed following activation, indicating that hyperacetylation of histone H3K9 may play a role in selective and rapid gene expression of memory CD8(+) T cells. Consistent with this model, we showed that inducing high levels of H3K9 acetylation resulted in an increased expression in naive cells of those genes that are normally expressed differentially in memory cells. Together, these findings suggest that differential gene expression mediated at least in part by histone H3K9 hyperacetylation may be responsible for the rapid and robust memory CD8(+) T-cell response.
Blood 12/2006; 108(10):3363-70. · 9.90 Impact Factor
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Catherine M Schwartz,
Charles E Spivak,
Shawn C Baker,
Timothy K McDaniel,
Jeanne F Loring,
Cuong Nguyen,
Francis J Chrest, Robert Wersto,
Ernest Arenas,
Xianmin Zeng,
William J Freed,
Mahendra S Rao
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ABSTRACT: NTera2, a human embryonal carcinoma (EC) stem cell line, shares many characteristics with human embryonic stem cells (hESCs). To determine whether NTera2 can serve as a useful surrogate for hESCs, we compared global gene expression between undifferentiated NTera2, multiple undifferentiated hESC cell lines, and their differentiated derivatives, and we showed that NTera2 cells share multiple markers with hESCs. Similar to hESCs, NTera2 cells differentiated into TH-positive cells that express dopaminergic markers including AADC, DAT, Nurr1, TrkB, TrkC, and GFRA1 when co-cultured with PA6 cells. Flow cytometry analysis showed that tyrosine hydroxylase (TH) and neural cell adhesion molecule (NCAM) expression increased, whereas SSEA4 expression decreased as cells differentiated. Medium conditioned by PA6 cells stimulated differentiation of NTera2 cells to generate TH-positive cells that expressed dopaminergic markers. Flow cytometry selected polysialylated (PSA-NCAM) cells responded to medium conditioned by PA6 cells by differentiating into TH-positive cells and expressed dopaminergic markers. Sorted cells differentiated for 4 weeks in PA6 cell conditioned media included functional neurons that responded to neurotransmitters and exhibited electronic excitability. Therefore, NTera2 cell dopaminergic neuronal differentiation and PSA-NCAM enrichment provides a useful system for the future study of hESCs.
Stem Cells and Development 11/2005; 14(5):517-34. · 4.46 Impact Factor
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ABSTRACT: Staurosporine and its derivative 7-hydroxystaurosporine are protein kinase inhibitors that are being considered for treatments of cancers. Several recent studies have shown that cells with defective pRB protein are resistant to the G(1) cell cycle-inhibiting effects of staurosporine compounds. In this study, we examined the effect of staurosporine on two breast cancer-derived and three lung cancer-derived cell lines characterized by deficiencies in the p16 tumor suppressor. All of these p16-deficient cell lines are highly sensitive to staurosporine-induced inhibition of pRB phosphorylation and induction of arrest in G(1). This response is similar to that seen in cultured normal human bronchial epithelial cells and normal mammary epithelial cells, but strikingly different than the staurosporine resistance seen in cancer cells with defective pRB. Interestingly, inhibition of pRB phosphorylation could be seen within 4 h of treatment, suggesting that this inhibition is a consequence of direct effects of staurosporine on protein kinase(s) rather than a result of induction of other cyclin-dependent kinase inhibitors. Our findings suggest that different types of cancer cells have vastly different responses to the staurosporine class of agents, and that evaluation of pRB and p16 will help predict the response of the cancer cells to these agents.
Cancer Letters 10/2002; 183(1):103-7. · 4.24 Impact Factor
