DISTINCT EFFECTS OF HEAT-SHOCK AND ATP DEPLETION ON DISTRIBUTION AND ISOFORM PATTERNS OF HUMAN HSP27 IN ENDOTHELIAL-CELLS

To study the cytoprotective capacity of Hsp27 under various cellular s tresses, we compared the effects of heating and energy deprivation on its distribution and isoform composition, Cultured endothelial cells f rom human aorta or umbilical vein were subjected to heat shock (45 deg rees C) and ATP-depleting metabolic stress (CCCP or rotenone in a gluc ose-free medium), Both exposures led to the translocation of Hsp27 int o the Triton X-100-insoluble cellular fraction, whereas the immunofluo rescent Hsp27 pattern was characteristic for each stress employed, Hea ting (5-30 min) caused unexpected association of Hsp27 with thick bund les of actin microfilaments (stress fibers), ATP depletion within 30-1 20 min resulted in the appearance of Hsp27-containing compact granules in the nucleus, The insolubilization and relocalization of Hsp27 were reversible in both cases, The stress-induced shifts in the Hsp27 isof orm spectrum indicate an increase in phosphorylation of Hsp27 in heat- shocked cells and its dephosphorylation in ATP-depleted cells. We sugg est that these stresses diversely affect the phosphorylation status of endothelial Hsp27, thus altering its localization, supramolecular org anization and functional activity toward actin.