The hsp70-associating protein Hap46 binds to DNA and stimulates transcription

Abstract

We investigated the ubiquitously expressed hsp70-associating protein Hap46, which is also called RAP46 and is homologous to BAG-1, for activities independent of hsp70 interactions. We observed in vitro binding to various DNA fragments but detected no apparent sequence specificity. Deletion of the amino-terminal decapeptide, which contains two clusters of three basic amino acids each, abolished the DNA-binding ability of Hap46. Similarly, exchange of either of these positively charged clusters for three alanines resulted in loss of DNA binding. Using a fusion of Hap46 and green f luorescent protein, we found preferential accumulation in cell nuclei on heat stress as compared with unstressed cells. The repressive effect of heat shock on overall transcriptional activity in human DU145 carcinoma cells was largely prevented when Hap46 was overexpressed by transfection. Such overproduction of Hap46 also resulted in enhanced expression of specific reporter gene constructs and in increased levels of mRNAs specific for hsp70 and hsp40 after temperature stress. In vitro transcription with nuclear extracts was stimulated greatly by Hap46. Like DNA binding, transcriptional enhancement required amino-terminally located basic amino acid residues but not the carboxyl-terminal portion of Hap46 known to participate in hsp70 interaction. Our results show that Hap46 is a bifunctional protein that can interact with both hsp70s and DNA, employing different portions of the molecule. They also suggest that Hap46 is involved in temperature-sensitive regulation of transcription, acting as a general transcriptional activator.

AtBAG6, a novel calmodulin-binding protein, induces programmed cell death in yeast and plants

“…[60][61][62][63][64][65][66][67][68][69] The functional diversity of BAG domain proteins is paralleled by an abundance of genes of this family throughout evolution, with homologs identified in a variety of organisms, including yeast, worm, invertebrates, amphibians, mammals, and plants. 21,59,60,70 Database searches indicate the presence of eight genes that encode proteins with the BAG domain in Arabidopsis thaliana.…”

The Corticosteroid Receptor Hypothesis of Depression

“…For example, hsp90 may participate in the nuclear-cytoplasmic shuttling of GR (Kang et al 1999) and it may also facilitate chromatin recycling of GR (Liu and DeFranco 1999). More recently, the cochaperone RAP 46 (also known as HAP 46 or BAG-IL) which can associate with hsp90 and GR has been identified as a non-specific DNA-binding protein which may act as a general transcriptional activator (Zeiner et al 1999), on the other hand, Schneikert and coworkers (1999) reported that RAP 46 downregulates GR-mediated transactivation, but not transrepression. Altogether, it becomes clear from these few selected examples that future research linking HPA function with causality of depression and course of treatment needs to include studies on the role of chaperones in GR signaling.…”

BAG‐1, An Anti‐Apoptotic Tumour Marker

“…Finally, BAG-1 may act as a general transcription factor for certain apoptosis genes. Under the heat shock-induced stress, BAG-1 bound to DNA directly and enhanced expression of specific reporter gene constructs (32). In addition, BAG-1 increased transcription of reporter gene constructs with different promoters in various cell types in the absence of thermal stress (33).…”