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Modulation of Drosophila heat shock transcription factor activity by the molecular chaperone DROJ1.

ABSTRACT: Heat shock transcription factors (HSFs) play important roles in the cellular response to physiological stress signals. To examine the control of HSF activity, we undertook a yeast two-hybrid screen for proteins interacting with Drosophila HSF. DROJ1, the fly counterpart of the human heat shock protein HSP40/HDJ1, was identified as the dominant interacting protein (15 independent isolates from 58 candidates). Overexpression of DROJ1 in Drosophila SL2 cells delays the onset of the heat shock response. Moreover, RNA interference involving transfection of SL2 cells with double-stranded droj1 RNA depletes the endogenous level of DROJ1 protein, leading to constitutive activation of endogenous heat shock genes. The induction level, modest when DROJ1 was depleted alone, reached maximal levels when DROJ1 and HSP70/HSC70, or DROJ1 and HSP90, were depleted concurrently. Chaperone co-depletion was also correlated with strong induction of the DNA binding activity of HSF. Our findings support a model in which synergistic interactions between DROJ1 and the HSP70/HSC70 and HSP90 chaperones modulate HSF activity by feedback repression.

SUBMITTER: Marchler G

PROVIDER: S-EPMC133474 | biostudies-literature | 2001 Feb

REPOSITORIES: biostudies-literature

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Modulation of Drosophila heat shock transcription factor activity by the molecular chaperone DROJ1.

Marchler G G Wu C C

The EMBO journal 20010201 3

Heat shock transcription factors (HSFs) play important roles in the cellular response to physiological stress signals. To examine the control of HSF activity, we undertook a yeast two-hybrid screen for proteins interacting with Drosophila HSF. DROJ1, the fly counterpart of the human heat shock protein HSP40/HDJ1, was identified as the dominant interacting protein (15 independent isolates from 58 candidates). Overexpression of DROJ1 in Drosophila SL2 cells delays the onset of the heat shock respo ...[more]

PMID: 11157756

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Project description:Small heat shock proteins (sHsps) are a ubiquitous part of the machinery that maintains cellular protein homeostasis by acting as molecular chaperones. sHsps bind to and prevent the aggregation of partially folded substrate proteins in an ATP-independent manner. sHsps are dynamic, forming an ensemble of structures from dimers to large oligomers through concentration-dependent equilibrium dissociation. Based on structural studies and mutagenesis experiments, it is proposed that the dimer is the smallest active chaperone unit, while larger oligomers may act as storage depots for sHsps or play additional roles in chaperone function. The complexity and dynamic nature of their structural organization has made elucidation of their chaperone function challenging. HspB1 and HspB5 are two canonical human sHsps that vary in sequence and are expressed in a wide variety of tissues. In order to determine the role of the dimer in chaperone activity, glutathione-S-transferase (GST) was genetically linked as a fusion protein to the N-terminus regions of both HspB1 and HspB5 (also known as Hsp27 and αB-crystallin, respectively) proteins in order to constrain oligomer formation of HspB1 and HspB5, by using GST, since it readily forms a dimeric structure. We monitored the chaperone activity of these fusion proteins, which suggest they primarily form dimers and monomers and function as active molecular chaperones. Furthermore, the two different fusion proteins exhibit different chaperone activity for two model substrate proteins, citrate synthase (CS) and malate dehydrogenase (MDH). GST-HspB1 prevents more aggregation of MDH compared to GST-HspB5 and wild type HspB1. However, when CS is the substrate, both GST-HspB1 and GST-HspB5 are equally effective chaperones. Furthermore, wild type proteins do not display equal activity toward the substrates, suggesting that each sHsp exhibits different substrate specificity. Thus, substrate specificity, as described here for full-length GST fusion proteins with MDH and CS, is modulated by both sHsp oligomeric conformation and by variations of sHsp sequences.

Dataset Information

Modulation of Drosophila heat shock transcription factor activity by the molecular chaperone DROJ1.

Publications

Modulation of Drosophila heat shock transcription factor activity by the molecular chaperone DROJ1.

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