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Frank Gannon

Publications and source records attributed to Frank Gannon.

At least 19 recordsLinked to original sources
PubMed2003

Cyclic, proteasome-mediated turnover of unliganded and liganded ERalpha on responsive promoters is an integral feature of estrogen signaling.

We present an integrated model of hERalpha-mediated transcription where both unliganded and liganded receptors cycle on estrogen-responsive promoters. Using ChIP, FRAP, and biochemical analysis we evaluate hERalpha at several points in these cycles, establishing the ubiquitination status and subnuclear distribution of hERalpha, its mobility, the kinetics of transcriptional activation, and the cyclic recruitment of E3 ligases and the 19S regulatory component of the proteasome. These experiments, together with an evaluation of the inhibition of transcription and proteasome action, demonstrate that proteasome-mediated degradation and hERalpha-mediated transactivation are inherently linked and act to continuously turn over hERalpha on responsive promoters. Cyclic turnover of hERalpha permits continuous responses to changes in the concentration of estradiol.

Blotting, Western↗
PubMed2002

Upstream open reading frames regulate the translation of the multiple mRNA variants of the estrogen receptor alpha.

It is by now well established that the estrogen receptor alpha (ER alpha) is transcribed from multiple promoters. One direct consequence of multiple promoters is the generation of mRNA variants with different 5'-untranslated regions (5'-UTRs). However, the potential roles of these individual mRNA variants are not known. All 5'-UTRs of ER alpha contain between one and six upstream open reading frames. In this study the effect of the 5'-UTRs of major human and mouse ER alpha mRNA variants on translation was evaluated. Some of the 5'-UTRs were found to strongly inhibit translation of the downstream open reading frame. Mutation of the upstream AUG codons partially or completely restored translation efficiency. A toeprinting analysis and assessment of the contribution of each AUG codon to the inhibitory effect on translation showed that leaky scanning and reinitiation occurs with these mRNAs. In conclusion, the upstream open reading frames in the 5'-UTRs of ER alpha mRNAs have the potential to regulate estrogen receptor alpha expression.

5' Untranslated Regions↗
PubMed2002

Formation of an hER alpha-COUP-TFI complex enhances hER alpha AF-1 through Ser118 phosphorylation by MAPK.

The enhancement of the human estrogen receptor alpha (hER alpha, NR3A1) activity by the orphan nuclear receptor COUP-TFI is found to depend on the establishment of a tight hER alpha-COUP-TFI complex. Formation of this complex seems to involve dynamic mechanisms different from those allowing hER alpha homodimerization. Although the hER alpha-COUP-TFI complex is present in all cells tested, the transcriptional cooperation between the two nuclear receptors is restricted to cell lines permissive to hER alpha activation function 1 (AF-1). In these cells, the physical interaction between COUP-TFI and hER alpha increases the affinity of hER alpha for ERK2/p42(MAPK), resulting in an enhanced phosphorylation state of the hER alpha Ser118. hER alpha thus acquires a strengthened AF-1 activity due to its hyperphosphorylation. These data indicate an alternative interaction process between nuclear receptors and demonstrate a novel protein intercommunication pathway that modulates hER alpha AF-1.

Adenocarcinoma↗
PubMed2002

Natural trans-spliced mRNAs are generated from the human estrogen receptor-alpha (hER alpha) gene.

The human estrogen receptor-alpha (hER alpha) gene is a complex genomic unit exhibiting alternative splicing and promoter usage in a tissue-specific manner. During the investigation of new hER alpha mRNA variants by rapid amplification of 5' cDNA ends, we identified a cDNA in which the acceptor site of exon 1A, into which the different leader exons are normally alternatively spliced, was spliced accurately the 3' extremity of exon 1A (scrambled 1A-->1A hER alpha cDNA). Reverse transcription-PCR and S1 nuclease mapping analysis revealed that 1A-->1A hER alpha transcripts were not circular RNAs constituted by exon 1A only but corresponded to linear polyadenylated hER alpha RNAs composed of the eight coding exons of the hER alpha gene and characterized by a duplication of exon 1A. Genomic Southern blot experiments excluded the hypothesis of duplication of hER alpha exon 1A in the human genome. Therefore, these data suggested that 1A-->1A hER alpha transcripts were likely generated by trans-splicing. The production of such transcripts by trans-splicing of pre-mRNAs generated from a chimeric gene formed by a single hER alpha exon 1A, exon 2, and their flanking intronic regions was demonstrated in transient transfection experiments. Therefore, in addition to the alternative cis-splicing, the hER alpha gene is also subject to natural trans-splicing.

Alternative Splicing↗
PubMed2002

A dynamic structural model for estrogen receptor-alpha activation by ligands, emphasizing the role of interactions between distant A and E domains.

The functional interplay between different domains of estrogen receptor-alpha (ERalpha, NR3A1) is responsible for the overall properties of the full-length protein. We previously identified an interaction between the N-terminal A and C-terminal domains, which we demonstrate here to repress ligand-independent transactivation and transrepression abilities of ERalpha. Using targeted mutations based on ERalpha structural models, we determine the basis for this interaction that defines a regulatory interplay between ERalpha A domain, corepressors, and ERalpha Helix 12 for binding to the same C-terminal surface. We propose a dynamic model where binding of different ligands influences the A/D-F domain interaction and results in specific functional outcomes. This model gives insights into the dynamic properties of full-length ERalpha and into the structure of unliganded ERalpha.

Amino Acid Sequence↗
PubMed2002

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Animal Experimentation↗