Dynamics of chaperone complex Hdj1-Hsp70-Bag1 as a response of erythroleukemia K562 cells to heat stress

Heat shock protein Hsp70 is known to play an important role in cell protection against a variety of harmful factors. This property, at least in part, is due to Hsp70 ability to restore the native conformation of newly synthetized or damaged proteins. In this activity Hsp70 is accompanied by two proteins, Hdj1 and Bag1, that enable Hsp70 to peform cycles of binding-release of target proteins. The aim of this study was to investigate interactions of Hdj1 and Bag1 co-chaperones with Hsp70 in vivo. The accumulation of Hsp70 was stimulated by heat stress, and later, at certain periods following the stress, cell probes were collected for biochemical and microscopic analysis. The data of Western blotting showed that within 24 h after heat shock amounts of Hsp70 and Hdj1 raised to remain at the elevated level for nearly 48 h. Several time points within this period were chosen for analysis of the complexes between Hsp70 and co-chaperones. The data of reciprocal immunoprecipitation/immunoblotting and confocal microscopy showed that Hsp70-Hdj1 complexes were detected primarily at early stage after heat shock, then Hsp70 was preferably bound to Bag1. The dynamics of chaperone complex formation and changes in their intracellular localization are discussed in terms of cell reaction to stress