RESUMEN
Androgen dependence of the mouse sex-limited protein (Slp) gene is conferred by an enhancer encompassing a consensus hormone response element (HRE) and sites for several nonreceptor factors. The footprint IV (FPIV) region of the enhancer plays a key role in hormone- and tissue-specific response, both in vitro and in vivo. We characterized FPIV-binding factors by methylation interference analysis and UV cross-linking of several complexes evident in gel mobility-shift assays. The footprinting analysis revealed that distinct base contacts within the multiple nuclear protein-DNA complexes occurred primarily within a sequence similar to an octamer transcription factor (Oct-1) binding site. With additional data on approximate molecular weights from UV cross-linking, several plausible candidates were tested for their DNA binding and functional activity at FPIV. Oct-like protein binding in gel-shift assays with several cell and tissue extracts was evident using specific competitors and antibodies, but was lower in affinity for FPIV than for an Oct-1 consensus site. Site-directed mutation of the FPIV sequence to a consensus Oct-1 element within the Slp enhancer context increased Oct-1 binding in vitro, but greatly reduced hormonal induction in vivo. This suggested that Oct-1 is not directly involved in response, or alternatively, that Oct-1 bound to the lower-affinity site interacts with neighboring factors significantly differently than Oct-1 bound to a consensus sequence. A sequence overlapping the Oct-like element that was similar to a hepatic nuclear factor-4 (HNF-4) site showed no ability to bind HNF-4 in vitro, nor the related orphan receptor, chicken ovalbumin upstream promoter factor (COUP-TF). Intriguingly, however, expression of COUP-TF in transfection had a dramatic inhibitory effect on response of the androgen-specific enhancer (C' delta9), but did not affect other enhancer configurations that can also be induced by glucocorticoid (C 'delta2). This underscores that, despite extensive sequence identity of C' delta9 and C' delta2, components of the androgen-specific transcription complex differ significantly from that of one that is more generally steroid responsive.
Asunto(s)
Andrógenos/fisiología , Proteínas Sanguíneas/genética , Proteínas de Unión al ADN/metabolismo , Elementos de Facilitación Genéticos , Animales , Factor de Transcripción COUP I , Línea Celular , Complemento C4 , ADN/metabolismo , ADN/efectos de la radiación , Metilación de ADN , Proteínas de Unión al ADN/química , Regulación de la Expresión Génica , Factor C1 de la Célula Huésped , Riñón/metabolismo , Hígado/metabolismo , Ratones , Peso Molecular , Factor 1 de Transcripción de Unión a Octámeros , Reacción en Cadena de la Polimerasa , Unión Proteica , Factores de Transcripción/metabolismo , Rayos Ultravioleta , Uracilo/metabolismoRESUMEN
The enhancer of the mouse sex-limited protein (Slp) gene includes a consensus hormone response element (HRE) that interacts with several auxiliary elements for steroid induction. The 160-bp fragment. C' delta 2, confers response to androgen or glucocorticoid in transfection, while a 120-bp subfragment, C' delta 9, is activated only by androgen in some cells. Site-directed mutants were tested to identify elements affecting differential response of androgen or glucocorticoid receptors (AR, GR). While most mutations of C' delta 2 affected induction by either steroid similarly, disruptions of the consensus HRE or an octamer-like sequence were more severe for GR than AR activity. An HRE half-site was critical to androgen-specific induction of C' delta 9 but had little impact in the nonspecific C' delta 2 context. In DNase I footprinting, full-length AR and GR bound similarly to the consensus HRE but dissimilarly to nonconsensus sites. Intriguingly, NF-kappa B bound the region of C' delta 2 absent from C' delta 9. Expression of I kappa B decreased response of C' delta 2, but not C' delta 9, confirming a permissive role of NF-kappa B in steroid activation. In this case, different factors may associate with receptors in the presence of NF-kappa B than those that confer androgen specificity in NF-kappa B's absence, suggesting that exclusion of some factors from a specific transcription complex is as crucial as inclusion of others. This dissection of C' delta 2 and C' delta 9 in vitro reveals subtle distinctions in AR and GR interactions that may underlie specific hormonal response in vivo.
Asunto(s)
Andrógenos/metabolismo , Proteínas Sanguíneas/genética , Elementos de Facilitación Genéticos , Glucocorticoides/metabolismo , FN-kappa B/metabolismo , Receptores de Esteroides/metabolismo , Animales , Secuencia de Bases , Línea Celular , Chlorocebus aethiops , Complemento C4 , Secuencia de Consenso , Ratones , Datos de Secuencia Molecular , Mutagénesis Sitio-Dirigida , Oligodesoxirribonucleótidos , Ratas , Células Tumorales CultivadasRESUMEN
A hormonally responsive enhancer that is specifically activated by androgens resides 2 kilobases upstream of the transcription start site of the mouse sex-limited protein (Slp) gene. We have previously shown that strong androgen induction in transfection requires a consensus hormone response element as well as several nonreceptor factor binding sites within this complex enhancer. To determine which accessory elements are required for androgen-dependent transcription, we have examined binding of nuclear proteins to the enhancer both in vitro and in vivo. In vitro footprinting assays demonstrated that multiple factors present in mouse liver and kidney nuclear extracts bound the enhancer, with tissue-specific but not sex-dependent differences in pattern. In contrast, examination of DNA sites occupied in liver chromatin identified a footprint (FPIV) that is well protected in males but sensitive to DNase I in females. FPIV was occupied in males in other sites of Slp expression, such as kidney, but not in tissues lacking expression, such as lung. FPIV protection was induced in females treated with androgen, abrogated in castrated males, and absent in immature mice, implying hormonal and developmental regulation of FPIV binding. Protection of the hormone response element, in contrast to FPIV, was not obvious but was discerned by analysis of densitometry data. Together with results from in vivo protein-DNA interactions determined for other steroid-dependent enhancers, this suggests that in some cases receptor may permit transcriptional activation by altering chromatin structure to allow access to other factors, which may not necessitate tight binding of receptor itself. This further emphasizes the crucial role of the nonreceptor factors in hormone response. The ubiquitous transcription factor Oct-1 forms complexes with an octamer motif present within FPIV by gel shift analysis with liver and kidney extracts, making Oct-1 an intriguing candidate for partnership in androgen regulation.