Faculty Bibliography

Expression of the nuclear receptor interacting factor 3 (NRIF3) coregulator in a wide variety of breast cancer cells selectively leads to rapid caspase-2-dependent apoptotic cell death. A novel death domain (DD1) was mapped to a 30-amino acid region of NRIF3. Because the cytotoxicity of NRIF3 and DD1 seems to be cell type-specific, these studies suggest that breast cancer cells contain a novel 'death switch' that can be specifically modulated by NRIF3 or DD1. Using an MCF-7 cell cDNA library in a yeast two-hybrid screen, we cloned a factor that mediates apoptosis by DD1 and refer to this factor as DD1-interacting factor-1 (DIF-1). DIF-1 is a transcriptional repressor that mediates its effect through SirT1, and this repression is attenuated by the binding of NRIF3/DD1. DIF-1 expression rescues breast cancer cells from NRIF3/DD1-induced apoptosis. Small interfering RNA (siRNA) knockdown of DIF-1 selectively leads to apoptosis of breast cancer cells, further suggesting that DIF-1 plays a key role in NRIF3/DD1-mediated apoptosis. A protein kinase A inhibitor (H89) also elicits apoptosis of breast cancer cells but not of the other cell types examined, and DIF-1 also protects these cells from H89-mediated apoptosis. In addition, H89 incubation results in a rapid increase in NRIF3 levels and siRNA knockdown of NRIF3 protects breast cancer cells from H89-mediated apoptosis. Our results indicate that DIF-1 plays a key role in breast cancer cell survival and further characterizing this pathway may provide important insights into developing novel therapies to selectively target breast cancer cells for apoptosis

CCR4-NOT is an evolutionarily conserved, multicomponent complex known to be involved in transcription as well as mRNA degradation. Various subunits (e.g. CNOT1 and CNOT7/CAF1) have been reported to be involved in influencing nuclear hormone receptor activities. Here, we show that CCR4/CNOT6 and RCD1/CNOT9, members of the CCR4-NOT complex, potentiate nuclear receptor activity. RCD1 interacts in vivo and in vitro with NIF-1 (NRC-interacting factor), a previously characterized nuclear receptor cotransducer that activates nuclear receptors via its interaction with NRC. As with NIF-1, RCD1 and CCR4 do not directly associate with nuclear receptors; however, they enhance ligand-dependent transcriptional activation by nuclear hormone receptors. CCR4 mediates its effect through the ligand binding domain of nuclear receptors and small interference RNA-mediated silencing of endogenous CCR4 results in a marked decrease in nuclear receptor activation. Furthermore, knockdown of CCR4 results in an attenuated stimulation of RARalpha target genes (e.g. Sox9 and HoxA1) as shown by quantitative PCR assays. The silencing of endogenous NIF-1 also resulted in a comparable decrease in the RAR-mediated induction of both Sox9 and HoxA1. Furthermore, CCR4 associates in vivo with NIF-1. In addition, the CCR4-enhanced transcriptional activation by nuclear receptors is dependent on NIF-1. The small interference RNA-mediated knockdown of NIF-1 blocks the ligand-dependent potentiating effect of CCR4. Our results suggest that CCR4 plays a role in the regulation of certain endogenous RARalpha target genes and that RCD1 and CCR4 might mediate their function through their interaction with NIF-1

NCoA6 (also referred to as NRC, ASC-2, TRBP, PRIP and RAP250) was originally isolated as a ligand-dependent nuclear receptor interacting protein. However, NCoA6 is a multifunctional coregulator or coactivator necessary for transcriptional activation of a wide spectrum of target genes. The NCoA6 gene is amplified and overexpressed in breast, colon and lung cancers. NCoA6 is a 250 kDa protein which harbors a potent N-terminal activation domain, AD1; and a second, centrally-located activation domain, AD2, which is necessary for nuclear receptor signaling. The intrinsic activation potential of NCoA6 is regulated by its C-terminal STL regulatory domain. Near AD2 is an LxxLL-1 motif which interacts with a wide spectrum of ligand-bound NRs with high-affinity. A second LxxLL motif (LxxLL-2) located towards the C-terminal region is more restricted in its NR specificity. The potential role of NCoA6 as a co-integrator is suggested by its ability to enhance transcriptional activation of a wide variety of transcription factors and from its in vivo association with a number of known cofactors including CBP/p300. NCoA6 has been shown to associate with at least three distinct coactivator complexes containing Set methyltransferases as core polypeptides. The composition of these complexes suggests that NCoA6 may play a fundamental role in transcriptional activation by modulating chromatin structure through histone methylation. Knockout studies in mice suggest that NCoA6 is an essential coactivator. NCoA6-/- embryos die between 8.5-12.5 dpc from general growth retardation coupled with developmental defects in the heart, liver, brain and placenta. NCoA6-/- MEFs grow at a reduced rate compared to WT MEFs and spontaneously undergo apoptosis, indicating the importance of NCoA6 as a prosurvival and anti-apoptotic gene. Studies with NCoA6+/- and conditional knockout mice suggest that NCoA6 is a pleiotropic coregulator involved in growth, development, wound healing and maintenance of energy homeostasis

Nuclear receptor coregulator (NRC) is a 250-kDa nuclear protein involved in transcriptional activation of nuclear hormone receptors, nuclear factor-kappaB, c-Jun, c-Fos, and cAMP response element-binding protein. NRC is organized into a modular structure consisting of two activation domains (AD1 and AD2), two nuclear hormone receptor-interacting motifs, LxxLL-1 and LxxLL-2, and a C-terminal regulatory region rich in serines, threonines, and leucines. The LxxLL-1 motif of NRC binds to a broad spectrum of nuclear hormone receptors with high affinity whereas LxxLL-2 interacts with a very limited number of receptors. In this study we present further evidence that NRC can act as a dimer and have identified a dimerization region of 146 amino acids including LxxLL-1. Mutation of the core LxxLL-1 motif, however, indicates that it is not involved in the dimerization of NRC. AD2, just C-terminal of LxxLL-1, was found to play a central role in ligand-dependent activation by nuclear receptors even though AD1 exhibits more potent intrinsic activity. Thus, a short region of approximately 300 amino acids including and flanking LxxLL-1 plays an important role in NRC dimerization and nuclear receptor binding and transcriptional activation. In addition, consistent with its role as a cointegrator for transcriptional activation, NRC also functions as a coactivator for signal transducer and activator of transcription 2 (STAT-2) and p53. Activation of p53 by NRC appears to involve a novel mechanism where NRC interacts indirectly with p53 through Trap80, a member of the mediator complex, which binds NRC interacting factor-1 (NIF-1), which interacts with and potentiates the effect of NRC

We previously reported that amino acids 20 to 50 of nuclear receptor interacting factor-3 mediates rapid apoptosis in breast cancer cell lines but not in cells derived from other tissues. We refer to this short region as death domain-1 (DD1). Small interfering RNA studies indicated that DD1-mediated apoptosis is caspase-2 dependent. In this study, we examined DD1-mediated apoptosis in more detail and generated stable caspase-2 knockdown breast cancer cells. These cells are resistant to DD1-mediated apoptosis. Time-lapse movies suggested that DD1-mediated apoptosis also leads to a "bystander effect." We found that within 5 h of DD1 expression, breast cancer cells release a factor(s) into the medium that leads to apoptosis of naive breast cancer cells or DD1-resistant cells (e.g., HeLa). The DD1-expressing caspase-2 knockdown cells also release a factor(s) that kills other cells, indicating that this effect is not dependent on the apoptogenic process. The bystander effect seems dependent on the production of reactive oxygen species (ROS). These and other studies indicate that DD1 expression in breast cancer cells leads to at least two death signals: one involving the rapid production of ROS and/or other soluble factors that directly or indirectly leads to a bystander effect and a second caspase-2-dependent process that leads to apoptosis in cells in which DD1 is expressed.

A subset of papillary renal cell carcinomas (RCC) is characterized by the expression of a TFE3 fusion protein, where the fusion partner can be any of the several proteins identified so far such as PSF (PTB associated splicing factor), NonO, PRCC, CLTC and ASPL. These proteins result from chromosomal translocations involving the TFE3 gene located on the X chromosome. Our present study documents the central role of PSF-TFE3 in oncogenic transformation. We show that the inhibition of PSF-TFE3 expression through siRNA or shRNA leads to impaired growth, proliferation, invasion potential and long-term survival of UOK-145 papillary renal carcinoma-derived cells, which endogenously express PSF-TFE3. The oncogenic potential of PSF-TFE3 became evident by stable expression of PSF-TFE3 in NIH-3T3 mouse fibroblast cells, which leads to the acquisition of anchorage-independent growth as revealed by soft agar assay. In addition, the expression of PSF-TFE3 in normal renal proximal tubular epithelial cells from where such tumors originate leads to dedifferentiation and loss of some key functional proteins, which may reflect an initial step in the multistep process of tumor development. This suggests that the expression of PSF-TFE3 in renal epithelial cells plays an important role in the initiation and maintenance of oncogenic phenotype in papillary RCC

The purpose of this study is to determine the feasibility of the direct matrix-assisted laser desorption/ionization (MALDI) identification of proteins in fixed T47D breast cancer cells and murine brain tissues. The ability to identify proteins from cells and tissue may lead to biomarkers that effectively predict the onset of defined disease states, and their dynamic behavior could be an important hint for drug target discoveries. Direct tissue application of trypsin allows protein identification in cells and tissues, while maintaining spatial integrity and intracellular organization. Using a chemical printer, matrix was co-registered on trypsinized human T47D breast cancer cells and cryo-preserved sections of murine brain tissue, followed by MALDI post-source decay (PSD) or MALDI collision-induced dissociation (CID), respectively. Mass-to-charge (m/z) data from the cells and brain tissues were processed using Mascot software interrogation of the National Center for Biotechnology Information (NCBI) database. Histone H2B was identified from cultured T47D human breast cancer cells. Tubulin beta2 was identified from mouse brain cortex following an induced stroke. These results suggest that MALDI PSD/CID, combined with bioinformatics, can be used for the direct identification of proteins from cells and tissues. Refinements in preparation techniques may improve this approach to provide a tool for quantitative proteomics and clinical analysis

Thyroid hormone receptors (TRs), expressed as TRalpha1, TRbeta1, and TRbeta2 isoforms, are members of the steroid hormone nuclear receptor gene superfamily, which comprises ligand-dependent transcription factors. The TR isoforms differ primarily in their N-terminal (A/B) domains, suggesting that the A/B regions mediate distinct transcriptional activation functions in a cell type-dependent or promoter-specific fashion. The nuclear receptor ligand-binding domain (LBD) undergoes a conformational change upon ligand binding that results in the recruitment of coactivators to the LBD. For glucocorticoid receptor and estrogen receptor-alpha, the same coactivator can contact both the LBD and A/B domains, thus leading to enhanced transcriptional activation. Very little is known regarding the role of the A/B domains of the TR isoforms. The A/B domain of TRbeta2 exhibits higher ligand-independent transcriptional activity than the A/B regions of TRalpha1 or TRbeta1. Thus, we examined the role of the A/B domain and the LBD of rat TRbeta2 in integrating the transcriptional activation function of the A/B and LBD domains by different coactivators. Both domains are essential for a productive functional interaction with cAMP response element-binding protein (CREB)-binding protein (CBP), and we found that CBP binds to the A/B domain of TRbeta2 in vitro. In contrast, steroid receptor coactivator-1a (SRC-1a) interacts strongly with the LBD but not the A/B domain. The coactivator NRC (nuclear receptor coactivator) interacts primarily with the LBD, although a weak interaction with the A/B domain further enhances ligand-dependent binding with TRbeta2. Our studies document the interplay between the A/B domain and the LBD of TRbeta2 in recruiting different coactivators to the receptor. Because NRC and SRC-1a bind CBP, and CBP enhances ligand-dependent activity, our studies suggest a model in which coactivator recruitment of NRC (or SRC-1a) occurs primarily through the LBD whereas the complex is further stabilized through an interaction of CBP with the N terminus of TRbeta2