Current Research and Scholarly Interests
Seek to understand the molecular mechanism by which human telomerase (hTERT) promoter mutations contribute to the biology of tumor cells.
Multiple modes of regulation of the human Ino80 SNF2 ATPase by subunits of the INO80 chromatin-remodeling complex.
Proceedings of the National Academy of Sciences of the United States of America
2013; 110 (51): 20497-502
SNF2 family ATPases are ATP-dependent motors that often function in multisubunit complexes to regulate chromatin structure. Although the central role of SNF2 ATPases in chromatin biology is well established, mechanisms by which their catalytic activities are regulated by additional subunits of chromatin-remodeling complexes are less well understood. Here we present evidence that the human Inositol auxotrophy 80 (Ino80) SNF2 ATPase is subject to regulation at multiple levels in the INO80 chromatin-remodeling complex. The zinc finger histidine triad domain-containing protein Ies2 (Ino Eighty Subunit 2) functions as a potent activator of the intrinsic catalytic activity of the Ino80 ATPase, whereas the YL-1 family Ies6 (Ino Eighty Subunit 6) and actin-related Arp5 proteins function together to promote binding of the Ino80 ATPase to nucleosomes. These findings support the idea that both substrate recognition and the intrinsic catalytic activities of SNF2 ATPases have evolved as important sites for their regulation.
View details for DOI 10.1073/pnas.1317092110
View details for PubMedID 24297934
Subunit Organization of the Human INO80 Chromatin Remodeling Complex AN EVOLUTIONARILY CONSERVED CORE COMPLEX CATALYZES ATP-DEPENDENT NUCLEOSOME REMODELING
JOURNAL OF BIOLOGICAL CHEMISTRY
2011; 286 (13): 11283-11289
We previously identified and purified a human ATP-dependent chromatin remodeling complex with similarity to the Saccharomyces cerevisiae INO80 complex (Jin, J., Cai, Y., Yao, T., Gottschalk, A. J., Florens, L., Swanson, S. K., Gutierrez, J. L., Coleman, M. K., Workman, J. L., Mushegian, A., Washburn, M. P., Conaway, R. C., and Conaway, J. W. (2005) J. Biol. Chem. 280, 41207-41212) and demonstrated that it is composed of (i) a Snf2 family ATPase (hIno80) related in sequence to the S. cerevisiae Ino80 ATPase; (ii) seven additional evolutionarily conserved subunits orthologous to yeast INO80 complex subunits; and (iii) six apparently metazoan-specific subunits. In this report, we present evidence that the human INO80 complex is composed of three modules that assemble with three distinct domains of the hIno80 ATPase. These modules include (i) one that is composed of the N terminus of the hIno80 protein and all of the metazoan-specific subunits and is not required for ATP-dependent nucleosome remodeling; (ii) a second that is composed of the hIno80 Snf2-like ATPase/helicase and helicase-SANT-associated/post-HSA (HSA/PTH) domain, the actin-related proteins Arp4 and Arp8, and the GLI-Kruppel family transcription factor YY1; and (iii) a third that is composed of the hIno80 Snf2 ATPase domain, the Ies2 and Ies6 proteins, the AAA(+) ATPases Tip49a and Tip49b, and the actin-related protein Arp5. Through purification and characterization of hINO80 complex subassemblies, we demonstrate that ATP-dependent nucleosome remodeling by the hINO80 complex is catalyzed by a core complex comprising the hIno80 protein HSA/PTH and Snf2 ATPase domains acting in concert with YY1 and the complete set of its evolutionarily conserved subunits. Taken together, our findings shed new light on the structure and function of the INO80 chromatin-remodeling complex.
View details for DOI 10.1074/jbc.M111.222505
View details for Web of Science ID 000288797100040
View details for PubMedID 21303910
Role for human mediator subunit MED25 in recruitment of mediator to promoters by endoplasmic reticulum stress-responsive transcription factor ATF6a.
journal of biological chemistry
2013; 288 (36): 26179-26187
Transcription factor ATF6α functions as a master regulator of endoplasmic reticulum (ER) stress response genes. In response to ER stress, ATF6α translocates from its site of latency in the ER membrane to the nucleus, where it activates RNA polymerase II transcription of ER stress response genes upon binding sequence-specifically to ER stress response enhancer elements (ERSEs) in their promoter-regulatory regions. In a recent study, we demonstrated that ATF6α activates transcription of ER stress response genes by a mechanism involving recruitment to ERSEs of the multisubunit Mediator and several histone acetyltransferase (HAT) complexes, including Spt-Ada-Gcn5 (SAGA) and Ada-Two-A-containing (ATAC) (Sela, D., Chen, L., Martin-Brown, S., Washburn, M.P., Florens, L., Conaway, J.W., and Conaway, R.C. (2012) J. Biol. Chem. 287, 23035-23045). In this study, we extend our investigation of the mechanism by which ATF6α supports recruitment of Mediator to ER stress response genes. We present findings arguing that Mediator subunit MED25 plays a critical role in this process and identify a MED25 domain that serves as a docking site on Mediator for the ATF6α transcription activation domain.
View details for DOI 10.1074/jbc.M113.496968
View details for PubMedID 23864652
Endoplasmic Reticulum Stress-responsive Transcription Factor ATF6 alpha Directs Recruitment of the Mediator of RNA Polymerase II Transcription and Multiple Histone Acetyltransferase Complexes
JOURNAL OF BIOLOGICAL CHEMISTRY
2012; 287 (27): 23035-23045
The basic leucine zipper transcription factor ATF6α functions as a master regulator of endoplasmic reticulum (ER) stress response genes. Previous studies have established that, in response to ER stress, ATF6α translocates to the nucleus and activates transcription of ER stress response genes upon binding sequence specifically to ER stress response enhancer elements in their promoters. In this study, we investigate the biochemical mechanism by which ATF6α activates transcription. By exploiting a combination of biochemical and multidimensional protein identification technology-based mass spectrometry approaches, we have obtained evidence that ATF6α functions at least in part by recruiting to the ER stress response enhancer elements of ER stress response genes a collection of RNA polymerase II coregulatory complexes, including the Mediator and multiple histone acetyltransferase complexes, among which are the Spt-Ada-Gcn5 acetyltransferase (SAGA) and Ada-Two-A-containing (ATAC) complexes. Our findings shed new light on the mechanism of action of ATF6α, and they outline a straightforward strategy for applying multidimensional protein identification technology mass spectrometry to determine which RNA polymerase II transcription factors and coregulators are recruited to promoters and other regulatory elements to control transcription.
View details for DOI 10.1074/jbc.M112.369504
View details for Web of Science ID 000306495000060
View details for PubMedID 22577136
Cholesterol-dependent and - Independent CD40 internalization and signaling activation in cardiovascular endothelial cells
ARTERIOSCLEROSIS THROMBOSIS AND VASCULAR BIOLOGY
2007; 27 (9): 2005-2013
It remains elusive how CD40 endocytosis or clustering on the cell surface is induced by different forms of CD40 agonist. This study aims to investigate whether lipid rafts differentially regulate CD40 traffic and signaling in proinflammatory activation of cardiovascular endothelial cells (ECs).Using fluorescent microscopy and flow cytometry, we demonstrated that soluble CD40L and agonistic antibody G28.5 induced CD40 internalization via clathrin-independent pathway. Furthermore, depletion of cholesterol by methyl-beta-cyclodextrin (MCD) or siRNA knockdown of caveolin-1 efficiently blocked CD40 internalization, suggesting that caveolae-rafts pathway regulates CD40 internalization. In contrast, a membrane-bound CD40L mimic (megamer) triggered aggregation of CD40 rafts outside of the conventional cholera toxin B subunit-positive lipid rafts resistant to cholesterol depletion. Finally, both G28.5 and megamer induced CD40 translocation to Brij58-insoluble, low buoyant density rafts, a movement insensitive to cholesterol depletion. However, MCD effectively inhibited G28.5 but not megamer-induced CD40 activation, and such inhibition could be alleviated by cholesterol reconstitution, suggesting that 2 different raft structures of CD40 induced by G28.5 or megamer possess differential sensitivity to cellular cholesterol levels in downstream signaling.Depending on different forms of agonist, CD40 uses either a cholesterol-dependent or -independent mode for trafficking and signaling in ECs.
View details for DOI 10.1161/ATVBAHA.107.145961
View details for Web of Science ID 000249084700021
View details for PubMedID 17626904