Recruitment of Octamer Transcription Factors to DNA by Glucocorticoid Receptor

Abstract

Glucocorticoid receptor (GR) and octamer transcription factors 1 and 2 (Oct-1/2) interact synergistically to activate the transcription of mouse mammary tumor virus and many cellular genes. Synergism correlates with cooperative DNA binding of the two factors in vitro. To examine the molecular basis for these cooperative interactions, we have studied the consequences of protein-protein binding between GR and Oct-1/2. We have determined that GR binds in solution to the octamer factor POU domain. Binding is mediated through an interface in the GR DNA binding domain that includes amino acids C500 and L501. In transfected mammalian cells, a transcriptionally inert wild-type but not an L501P GR peptide potentiated transcriptional activation by Oct-2 100-fold above the level that could be attained in the cell by expressing Oct-2 alone. Transcriptional activation correlated closely with a striking increase in the occupancy of octamer motifs adjacent to glucocorticoid response elements (GREs) on transiently transfected DNAs. Intriguingly, GR-Oct-1/2 binding was interrupted by the binding of GR to a GRE. We propose a model for transcriptional cooperativity in which GR-Oct-1/2 binding promotes an increase in the local concentration of octamer factors over glucocorticoidresponsive regulatory regions. These results reveal transcriptional cooperativity through a direct protein interaction between two sequence-specific transcription factors that is mediated in a way that is expected to restrict transcriptional effects to regulatory regions with DNA binding sites for both factors.The initiation of transcription of genes by RNA polymerase II is usually controlled through complex transcriptional regulatory regions containing multiple binding sites for sequencespecific upstream transcription factors (74, 88). Overall transcriptional responsiveness is determined by cooperative and competitive interactions between the DNA-bound factors that are often dependent upon the precise juxtaposition of DNA binding sites (44). The regulatory potential of individual transcription factors can be influenced indirectly through the manipulation of DNA and/or chromatin structure (6,8,55,88,91). The precise arrangement of the transcription factor binding sites is also important for the cooperative interactions of sequence-specific transcription factors with transcriptional coactivators and the basal transcription machinery (43,53,62,80,94).In many instances, transcriptional cooperativity also correlates with direct protein-protein interactions between individual sequence-specific transcription factors. Often, protein-protein contacts between heterologous factors stabilize DNA binding or alter the sequence specificity of binding. Thus, DNA-bound serum response factor is required for the formation of a ternary complex which includes serum response factor accessory protein 1 (SAP-1) (90); the sequence-specific DNA binding of DNA-dependent protein kinase is mediated through its association with DNA-bound Ku autoantigen (30), and the interaction of herpe...

Nuclear Factor 1 and Octamer Transcription Factor 1 Binding Preset the Chromatin Structure of the Mouse Mammary Tumor Virus Promoter for Hormone Induction

“…5, A and B) may be due to the chromatin remodeling mediated by GR, presumably via recruitment of various nucleosome remodeling/coactivator complexes (44 -46). Alternatively, it may be due to a direct protein-protein contact between the GR DNA binding domain and Oct1, as has been reported before (30) and/or complex formation between NF1 and Oct1, as recently described to occur between NF1 and the homeobox containing thyroid transcription factor 1 (47). These different mechanisms may be operating concomitantly.…”

“…This revealed the importance of these two factors for basal as well as hormone-induced transcription at the MMTV promoter. Importantly, both NF1 (13,25) and Oct1 (13,30) were shown to be excluded from the inactive promoter and to gain access only in the hormone-activated state. These findings have led to the formulation of the "two-step" model as the mechanism for GRactivated MMTV transcription.…”

TALE Homeodomain Proteins Regulate Gonadotropin-releasing Hormone Gene Expression Independently and via Interactions with Oct-1

“…Furthermore, both Oct-1 and Pbx1 are required for glucocorticoid-mediated repression of the prolactin promoter (39). Functional analysis established that the DNA-binding domain of the glucocorticoid receptor is necessary for synergy with both proteins in the context of different promoters (50,51). Oct-1 has also been implicated in repression of GnRH transcription by the nitric oxide pathway (12).…”

The Binding of Ku Antigen to Homeodomain Proteins Promotes Their Phosphorylation by DNA-dependent Protein Kinase

“…pGEX2T-HOXC4 HD-Oct-1 POU sp was generated by cloning the Oct-1 POU-specific domain (aa 268 -369) in the SmaI site of plasmid PGEX2T-HOXC4 HD. pGSTOct-2 POU used in bandshift has been described (33).…”

“…The preparation of the recombinant Ku and GST-Oct2 POU peptide employed in these assays was as previously described (26,33). Antibodies 111 (NeoMarkers) and YL123 (Upstate Biotechnology) were added at the beginning of the incubations.…”