[The extracellular heat shock protein 70 and its functions].

Various stress factors induce the accumulation of intracellular heat shock proteins, in particular heat shock protein 70 (Hsp70), which is considered as the main component of cellular response to stress. Though initially Hsp70 was thought to be a typical intracellular protein, the strong evidence now exists demonstrating that the Hsp70 exits mammalian cells not only following necrotic cell death but also by a process involving its active release. This review discusses the mechanisms of Hsp70 release and immunomodulatory and signaling functions of extracellular Hsp70.

Extracellular HspBP1 and Hsp72 synergistically activate epidermal growth factor receptor.

Background Information: Heat-inducible Hsp72 is the founding member of the Hsp70 (heat shock proteins of 70 kDa) family of molecular chaperones. It is localized primarily in cytoplasm and nucleus but is also found extracellularly. The source of e-Hsp72 (extracellular Hsp72) is not precisely identified and may not be the same in every situation.

Extracellular heat shock protein 70 mediates heat stress-induced epidermal growth factor receptor transactivation in A431 carcinoma cells.

The initial steps of heat stress in A431 cells were previously characterized by ligand-independent EGFR transactivation via an unknown mechanism and concomitant secretion of Hsp70. In this work we demonstrate that the depletion of Hsp70 from the conditioned medium of heated cells abolishes EGFR transactivation indicating that secreted Hsp70 is essential for EGFR transactivation during heat shock. This notion is supported by the findings that purified Hsp70 can induce EGFR transactivation and the activation of EGFR-dependent signaling pathways.

[EGF-dependent signaling pathways are activated under heat stress in A431 carcinoma cells].

EGF receptor transactivation and activation of EGF-dependent signaling pathways under heat shock conditions were studied. Heating A431 cells at 42 degrees C induced both EGF receptor tyrosine phosphorylation and appearance of phosphorylated forms of key components of its downstream signaling pathways - phospholipase Cgamma1 (PLCgamma1), transcription factor STAT3, and EPK1/2. It is suggested that EGF receptor is transactivated under heat shock in A431 cells.