Small stress proteins: chaperones that act as regulators of intracellular redox state and programmed cell death.

Small stress proteins (sHsp) are molecular chaperones whose expression was shown to enhance the survival of mammalian cells exposed to numerous types of injuries that lead to death, including heat shock, oxidative stress as well as treatments with anti-cancerous and apoptosis-inducing agents. Here, a summary of the most recent results concerning the protective activity of this family of proteins against programmed cell death is presented. (1) sHsp enhance the survival of cells exposed to oxidative stress, a phenomenon which is linked to the ability of these proteins to decrease the intracellular level of reactive oxygen species in a glutathione dependent way. (2) sHsp protect against apoptosis mediated by different agents including staurosporine, etoposide and the Fas ligand. (3) An interesting and particular aspect of sHsp concerns their transient expression during the cell division to differentiation transition. In this context, sHsp expression was shown to be essential for preventing differentiating cells from undergoing apoptosis. Small stress proteins appear therefore as novel regulators that interfere with programmed cell death induced by different pathways.