The serum-induced phosphorylation of mammalian hsp27 correlates with changes in its intracellular localization and levels of oligomerization

Authors

  • Patrick MEHLEN,

    1. Laboratoire du Stress Cellulaire, Centre de Génétique Moleculaire and Cellulaire, CNRS-UMR 106, Université Claude Bernard, France
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  • André-Patrick ARRIGO

    Corresponding author
    1. Laboratoire du Stress Cellulaire, Centre de Génétique Moleculaire and Cellulaire, CNRS-UMR 106, Université Claude Bernard, France
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Correspondence to A.-P. Arrigo, Laboratoire du Stress Cellulaire, CNRS UMR 106, Centre de Génétique moléculaire, Université Claude Bernard, Lyon-I, 43, Boulevard du 11 Novembre 1918, F-69622 Villeurbanne Cédex, France
Fax: +33 72440555.

Abstract

The oligomeric small heat-shock protein hsp27, also denoted hsp28, is constitutively expressed in several mammalian cells and displays a phosphorylation status that is related to cellular growth and differentiation. This protein is related to α-crystallin and has strong sequence similarity with an in vitro inhibitor of actin polymerization. Here, we have analyzed hsp27 phosphorylation, cellular localization and structural organization following serum stimulation of serum-starved HeLa cells. hsp27 is dephosphorylated in starved cells and quantitatively recovered in the form of small structures (<200 kDa) present in the soluble phase of the cytoplasm. Immediately after the addition of serum to starved cells, a rapid phosphorylation and complex changes in the intracellular distribution and structural organization of hsp27 are observed. Phosphorylation essentially occurs at the level of small hsp27 structures (<200 kDa) and is concomitant with the increased molecular mass (up to 700 kDa) of a fraction of this protein. Serum treatment also induced the detergent-sensitive association of another fraction of hsp27, still in the form of small and dephosphorylated structures, with cellular particulate fractions. Contrasting with these observations, hsp70 had the tendency to concentrate into nucleoli during serum starvation.

Abbreviations
hsp

heat-shock protein

Ancillary