The E2F family of transcription factors regulates the temporal transcription of genes involved in cell cycle progression and DNA synthesis. E2F transactivation is antagonized by retinoblastoma protein (pRb), which recruits chromatin-remodeling proteins such as histone deacetylases and SWI⅐SNF complexes to the promoter to repress transcription. We hypothesized that E2F proteins must reverse the pRb-imposed chromatin structure to stimulate transcription. If this is true, E2F proteins should recruit proteins capable of histone acetylation. Here we map the E2F-4 transactivation domain and show that E2F-1 and E2F-4 transactivation domains bind the acetyltransferase GCN5 and cofactor TRRAP in vivo. TRRAP and GCN5 co-expression stimulated E2F-mediated transactivation, and c-Myc repressed E2F transactivation dependent on an intact TRRAP/GCN5 binding motif. The transactivation domain of E2F-4 recruited proteins with significant histone acetyltransferase activity in vivo, and this activity required catalytically active GCN5. E2F-4 proteins with subtle mutations in the transactivation domain exhibited a positive correlation among transcriptional activation and GCN5 and TRRAP binding capacity and associated acetyltransferase activity. We conclude that E2F stimulates transcription by recruiting acetyltransferase activity and the essential cofactors GCN5 and TRRAP. These results provide a mechanism for E2F transcription factors to overcome pRb-mediated dominant repression of transcription.The cell cycle is regulated in part by the temporal expression of specific genes. A transcription factor can control the timely induction of S phase-specific genes by either activating gene expression shortly before and during S phase or repressing expression during the remainder of the cell cycle. The E2F family of transcription factors is thought to contribute to cell cycle regulation through both mechanisms. E2F is likely to be a critical factor in cell growth regulation in vivo since most if not all human cancers contain a disruption in the E2F regulatory pathway (1).Consistent with this, enforced expression of E2F proteins drives quiescent cells into S phase and transforms cells in conjunction with activated Ras (2-6). Furthermore, E2F binding sites are found in the promoters of numerous genes whose expression is necessary for the initiation of S phase and DNA replication (7-9).DNA binding activity of the E2F transcription factor family is composed of two subunits, E2F and DP, which form heterodimeric complexes with a high affinity for the DNA sequence 5Ј-TTTCGCG-3Ј (7-9). Currently, the mammalian E2F family consists of six E2F and two DP genes. The DNA binding, heterodimerization, and marked box domains are highly conserved among all E2F family members. E2F-1, -2, and -3 have an extended N-terminal region containing a nuclear localization signal and binding sites for cyclin A, the transcription factor Sp1, and the E3 ubiquitin ligase complex SCF⅐SKP2 (10 -17). E2F-4, -5, and -6 lack these sequences. E2Fs 1-5 have an acidic transactivat...

The adenovirus E1A oncoprotein stimulates cell growth and inhibits differentiation by deregulating the normal transcription program via interaction with positive and negative cellular effectors. E1A associates with transcriptional regulatory complexes containing p400 and TRRAP involved in chromatin remodeling and decondensation. TRRAP is a component of three distinct human histone acetyltransferase (HAT) complexes: the TIP60 complex and complexes containing GCN5 or PCAF. We demonstrate here that E1A binds a TRRAP complex that contains the GCN5 acetyltransferase during a normal adenovirus infection. E1A binds GCN5 and TRRAP in vivo early after virus infection. E1A is associated with significant HAT activity in vitro that is partly attributable to GCN5. E1A represses c-Myc-and E2F-1-directed transcriptional activation in vivo by sequestering GCN5 and/or TRRAP. Our results demonstrate that E1A distinctly binds TRRAP/GCN5, p300/CBP and PCAF HAT complexes. Through interactions with multiple HAT complexes, E1A may deregulate cellular transcription programs and facilitate infection by recruiting functional HAT coactivators to viral and cellular promoter regions.

Historically, therapeutic protein production in Chinese hamster ovary (CHO) cells has been accomplished by random integration (RI) of expression plasmids into the host cell genome. More recently, the development of targeted integration (TI) host cells has allowed for recombination of plasmid DNA into a predetermined genomic locus, eliminating one contributor to clone‐to‐clone variability. In this study, a TI host capable of simultaneously integrating two plasmids at the same genomic site was used to assess the effect of antibody heavy chain and light chain gene dosage on antibody productivity. Our results showed that increasing antibody gene copy number can increase specific productivity, but with diminishing returns as more antibody genes are added to the same TI locus. Random integration of additional antibody DNA copies in to a targeted integration cell line showed a further increase in specific productivity, suggesting that targeting additional genomic sites for gene integration may be beneficial. Additionally, the position of antibody genes in the two plasmids was observed to have a strong effect on antibody expression level. These findings shed light on vector design to maximize production of conventional antibodies or tune expression for proper assembly of complex or bispecific antibodies in a TI system.

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FK506-binding protein 52 (FKBP52) is an immunophilin that possesses peptidylprolyl cis/trans-isomerase(PPIase) activity and is a component of a subclass of steroid hormone receptor complexes. Several recent studies indicate that immunophilins can regulate neuronal survival and nerve regeneration although the molecular mechanisms are poorly understood. To investigate the function of FKBP52 in the nervous system, we employed a yeast two-hybrid strategy using the PPIase domain (domain I) as bait to screen a neonatal rat dorsal root ganglia cDNA expression library. We identified an interaction between FKBP52 domain I and Atox1, a copper-binding metallochaperone. Atox1 interacts with Menkes disease protein and Wilson disease protein (WD) and functions in copper efflux. The interaction between FKBP52 and Atox1 was observed in both glutathione S-transferase pull-down experiments and when proteins were ectopically expressed in human embryonic kidney (HEK) 293T cells and was sensitive to FK506. Interestingly, the FKBP52/Atox1 interaction was enhanced when HEK 293T cells were cultured in copper-supplemented medium and decreased in the presence of the copper chelator, bathocuproine disulfate, suggesting that the interaction is regulated in part by intracellular copper. Overexpression of FKBP52 increased rapid copper efflux in 64 Cu-loaded cells, as did the overexpression of WD transporter. Taken together, our present findings suggest that FKBP52 is a component of the copper efflux machinery, and in so, may also promote neuroprotection from copper toxicity. FKBP521 is a high molecular weight FK506-binding immunophilin first identified as a component of steroid hormone receptor heterocomplexes (1). Analysis of mRNA and protein levels has demonstrated that FKBP52 is widely expressed in mammalian tissues but particularly abundant in the nervous system (2, 3). Structurally, FKBP52 contains an N-terminal peptidylprolyl cis-trans-isomerase (PPIase) domain (domain I), a FKBP-like pseudo domain (domain II), three tetratricopeptide repeat (TPR) domains (domain III) that mediate proteinprotein interactions with HSP90, and a C-terminal domain calmodulin-binding site (domain IV) (4, 5).FKBP52 has been shown to play important roles in a diverse number of intracellular processes, but much research has focused on its involvement in steroid hormone regulation. FKBP52 regulates the maturation of steroid hormone receptor complexes through interactions between its TPR domain and HSP90 chaperones, which act as scaffolds for receptor assembly and are thought to enhance the affinity of estrogen receptor and the glucocorticoid receptor toward their ligands (1, 6). The PPIase domain of FKBP52 facilitates translocation of the activated steroid receptors to the nucleus by binding to cytoplasmic dynein (7). FKBP52 serves as a transcriptional regulator by repressing the activity of interferon regulatory factor-4 in immune cells (8) and heat-shock factor-1 in HeLa cells (9). FKBP52 has been implicated in the cardiotrophic effect of cardiotrophin-1 (10...

In the development of biopharmaceutical products, the expectation of regulatory agencies is that the recombinant proteins are produced from a cell line derived from a single progenitor cell. A single limiting dilution step followed by direct imaging, as supplemental information, provides direct evidence that a cell line originated from a single progenitor cell. To obtain this evidence, a high-throughput automated imaging system was developed and characterized to consistently ensure that cell lines used for therapeutic protein production are clonally-derived. Fluorescent cell mixing studies determined that the automated imaging workflow and analysis provide ∼95% confidence in accurately and precisely identifying one cell in a well. Manual inspection of the images increases the confidence that the cell line was derived from a single-cell to >99.9%. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:584-592, 2018.

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