Expression of the Molecular Chaperone Hsp70 in Detergent-resistant Microdomains Correlates with Its Membrane Delivery and Release

Abstract

Accumulating evidence suggests that some heat shock proteins (Hsps), in particular the 72-kDa inducible Hsp70, associate to the cell membrane and might be secreted through an unknown mechanism to exert important functions in the immune response and signal transduction. We speculated that specialized structures named lipid rafts, known as important platforms for the delivery of proteins to the cell membrane, might be involved in the unknown mechanism ensuring membrane association and secretion of Hsp70. Lipid rafts are sphingolipid-cholesterol-rich structures that have been mainly characterized in polarized epithelial cells and can be isolated as detergent-resistant microdomains (DRMs). Analysis of soluble and DRM fractions prepared from unstressed Caco-2 epithelial cells revealed that Hsp70, and to a lesser extent calnexin, were present in DRM fractions. Increased expression of Hsps, through heat shock or by using drugs acting on protein trafficking or intracellular calcium level, induced an efficient translocation to DRM. We also found that Hsp70 was released by epithelial Caco-2 cells, and this release dramatically increased after heat shock. Drugs known to block the classical secretory pathway were unable to reduce Hsp70 release. By contrast, release of the protein was affected by the raft-disrupting drug methyl-␤-cyclodextrin. Our data suggest that lipid rafts are part of a mechanism ensuring the correct functions of Hsps and provide a rational explanation for the observed membrane association and release of Hsp70.

Major role of HSP70 as a paracrine inducer of cytokine production in human oxidized LDL treated macrophages

“…HSP70 release from epithelial cells is mediated by sphingolipid-cholesterol-rich structures named lipid rafts [11]. To study the mechanism of oxLDL-induced HSP70 release in human macrophages, the cells were depleted of cholesterol using methyl-β-cyclodextrin before oxLDL treatment.…”

“…Several studies have shown that HSP70 can be actively released from cultured cells via a mechanism suggested to involve lipid-rafts [11,26,27]. A recent study has demonstrated that this also occurs in mononuclear cells [28].…”

Monoclonal antibody to novel cell surface epitope on Hsc70 promotes morphogenesis of bile ducts in newborn rat liver

“…Hsp70 has also been shown to associate with lipid rafts (Broquet et al 2003). These lipid-based organizational platforms, enriched in glycosphingolipids and cholesterol, are located in plasma membranes and have been implicated in a number of biological functions including membrane trafficking and signal transduction (Simons and Ikonen 1997;Hanzal-Bayer and Hancock 2007;Patra 2008).…”

Potential immunological functions of salivary Hsp70 in mucosal and periodontal defense mechanisms

“…Consequently, transport [37,40] would require either increased cell membrane permeability [29] or a specific exocytotic pathway, as already was reported from a hepatosplanchnic source [28] and from the brain [45] following body exercise. A possible way of specific exocytotic transport via an alternative vesicular pathway not involving the endoplasmic reticulum-Golgi compartment was already reported [13]. This alternative transport of Hsp70 may occur either through lipid rafts or through exosomes [44].…”