TUMOR-NECROSIS-FACTOR-ALPHA INDUCES CHANGES IN THE PHOSPHORYLATION, CELLULAR-LOCALIZATION, AND OLIGOMERIZATION OF HUMAN HSP27, A STRESS PROTEIN THAT CONFERS CELLULAR-RESISTANCE TO THIS CYTOKINE

The stress protein hsp27 is constitutively expressed in several human cells and shows a rapid phosphorylation following treatment with tumor necrosis factor-alpha (TNF-alpha). hsp27 usually displays native mole cular mass ranging from 100 to 700 kDa. Here, we have analyzed the TNF -alpha-mediated changes in the phosphorylation, cellular localization, and structural organization of hsp27 in HeLa cells. We report that th e TNF-alpha-mediated hsp27 phosphorylation is a long-lasting phenomeno n that correlates with the cytostatic effect of this cytokine. Followi ng TNF-alpha treatment, the rapid phosphorylation of hsp27 occurred co ncomitantly with complex changes in the intracellular distribution and structural organization of this protein. This resulted in the quantit ative redistribution of hsp27 toward the soluble phase of the cytoplas m. In addition, during the first 2 h of TNF-alpha treatment, a transie nt increase in the native molecular mass of most hsp27 molecules (less than or equal to 700 kDa) occurred. Then, by 4 h of TNF-(alpha treatm ent, the native size of this stress protein drastically regressed (<20 0 kDa). During this phenomenon, the phosphorylated isoforms of hsp27 r emained concentrated in the small or medium-sized oligomers (<300 kDa) of this protein. We also analyzed the properties of human hsp27 in tr ansfected murine L929 cell lines that constitutively express this prot ein. in these cells, TNF-alpha induced modifications in the phosphoryl ation, intracellular distribution, and oligomerization of human hsp27 similar to those observed in HeLa cells. Moreover, the expression of h sp27 in L929 cells was found to correlate with a reduced cytotoxicity of this cytokine. Hence, the complex changes in the phosphorylation, i ntracellular locale and structural organization of human hsp27 may be related to the protective activity of this protein against the deleter ious effects induced by TNF-alpha.