Interaction of Drosophila 27,000 Mr heat-shock protein with the nucleus of heat-shocked and ecdysone-stimulated culture cells.

The intracellular localization and expression of hsp27 (heat-shock protein 27) were investigated by cellular fractionation and immunofluorescence microscopy in Drosophila S3 cells. In unstressed cells, hsp27 is expressed in only 2% of the cells, whereas following heat shock, during recovery or after induction by ecdysone, the protein is detected in all cells. Under all these conditions, hsp27 appears to be concentrated in the nuclear region as revealed by immunofluorescence. During heat shock, this hsp is localized primarily in the nucleus with an enrichment in the perinucleolar region. However, the cellular fractionation data indicate that the nature of hsp27 interaction with nuclear components greatly differs depending on whether or not cells were subjected to elevated temperatures. After heat shock, hsp27 is resistant to non-ionic detergent extraction. In cells allowed to recover at normal temperature and in those where its synthesis was induced by the molting hormone, ecdysone, this hsp is readily solubilized by detergent. These data suggest that, following heat shock, hsp27 may become physically associated with some nuclear component(s) that are resistant to detergent extraction.