Targeting of the Hsp function in
tumor cells is currently being assessed as potential anticancer
therapy. An improved understanding of the molecular signals that trigger or attenuate the
stress protein response is essential for advances to be made in this field. The present study provides evidence that the membrane fluidizer
benzyl alcohol (BA), a documented nondenaturant, acts as a chaperone inducer in B16(F10)
melanoma cells. It is demonstrated that this effect relies basically on
heat shock transcription factor 1 (HSF1) activation. Under the conditions tested, the BA-induced Hsp response involves the up-regulation of a subset of hsp genes. It is shown that the same level of membrane fluidization (estimated in the core membrane region) attained with the closely analogous
phenethyl alcohol (PhA) does not generate a
stress protein signal. BA, at a concentration that activates heat shock genes, exerts a profound effect on the melting of raft-like
cholesterol-
sphingomyelin domains in vitro, whereas PhA, at a concentration equipotent with BA in membrane fluidization, has no such effect. Furthermore, through the in vivo labeling of
melanoma cells with a
fluorescein labeled probe that inserts into the
cholesterol-rich membrane domains [
fluorescein ester of
polyethylene glycol-derivatized
cholesterol (
fPEG-Chol)], we found that, similarly to heat stress per se, BA, but not PhA, initiates profound alterations in the plasma membrane microdomain structure. We suggest that, apart from membrane hyperfluidization in the deep hydrophobic region, a distinct reorganization of
cholesterol-rich microdomains may also be required for the generation and transmission of stress signals to activate hsp genes.