Hsp70 accelerates the recovery of nucleolar morphology after heat shock.

Abstract

The major heat-shock protein, hsp7O, is synthesized by cells of many organisms in response to stress. In the present study, Drosophila hsp7O was expressed from cloned genes in mouse L cells and monkey COS cells and detected by immunofluorescence using monoclonal antibodies. Hsp7O is found mostly but not exclusively in the nucleus of unstressed cells. For several hours after a short heat shock, however, it is strongly concentrated in nucleoli. Nucleoli are transiently damaged by such a heat shock: their morphology changes and assembly and export of ribosomes is blocked for several hours. This block can be visualized by addition of actinomycin D: under normal conditions pre-ribosomes are chased out of nucleoli, and the latter shrink dramatically, but no such shrinking is seen in heat-shocked cells. High levels of hsp7O can be produced in unstressed COS cells by transfecting them with an appropriate expression plasmid. Such cells show a more rapid recovery of nucleolar morphology following a heat shock than do untransfected cells. Furthermore, heat shock does not prevent shrinkage of their nucleoli in the presence of actinomycin, which indicates that ribosome export also recovers rapidly when pre-synthesized hsp7O is present. I suggest that an important function of hsp7O is to catalyze reassembly of damaged pre-ribosomes and other RNPs after heat shock.

Heat Shock Proteins hsp60 and hsp70: Their Roles in Folding, Assembly and Membrane Translocation of Proteins

“…Nucleoli are heat sensitive and exhibit an altered morphology after heat shock. The recovery of nucleolar morphology occurred more rapidly in the presence of a constitutively expressed hsp70 in the cell, even when synthesis of other heat shock proteins was blocked (PELHAM 1984). This indicates an involvement of the protein in repair processes of RNP structures.…”

Gold nanoparticles induce nuclear damage in breast cancer cells, which is further amplified by hyperthermia

“…The nucleolar accumulation of hsc70 is a well-established heat shock response that is likely linked to the proper organization and function of nucleoli [42,53,54]. When compared to vehicle or other GNPs, gold nanoflowers led to a small reduction of nucleolar hsc70 after heat shock (Fig.…”

Heat shock gene expression and cytoskeletal alterations in mouse neuroblastoma cells

“…Although many recovery processes seem to be mediated by proteins synthesized during the recovery period (see for instance Refs. [25,26]), the re-formation of the cytoskeleton appeared to occur independently of protein synthesis.…”