Expression of the anti-apoptotic protein Hsp27 during both the keratinocyte differentiation and dedifferentiation of HaCat cells: expression linked to changes in intracellular protein organization?

We show here that Hsp27 increases its level of expression during the late phase of the keratinocyte differentiation of human HaCat cells. A similar phenomenon was observed when differentiated HaCat cells underwent a dedifferentiation process. In both cases, Hsp27 accumulated in the form of large native structures, which represent the chaperone active form of the protein. Hence, the presence of Hsp27 large oligomers does not appear to be the consequence of a particular differentiation process but should be considered as a marker of endogenous stress conditions. Such conditions may arise when drastic changes in the intracellular protein organization occur, such as during differentiation, dedifferentiation and probably also during the development of the senescent phenotype.