Tumor-specific Hsp70 plasma membrane localization is enabled by the glycosphingolipid Gb3

Background: Human tumor differ from normal tissues in thier capacity to present Hsp70, the major stress inducible member of HSP70 family, on their plasma membrane. Membrane Hsp70 has been found to serve as a prognostic indicator of overall patient survival in leukemia, lower rectal and non small cell lung carcinomas. Why tumors, but not normal cells, present Hsp70 on their cell surface and the impact of membrane Hsp70 on cancer progression remains to be elucidated. Methodology/Principal Findings: Although Hsp70 has been reported to be associated with cholesterol rich microdomains (CRMs), the partener in the plasma membrane with which Hsp70 interacts has yet to be identified. Herein, global lipid profiling demonstrates mthat Hsp70 membrane-positive tumors differ from their membrane negative counterparts by containing significantly higher amounts of globotriaoslyceramide (Gb3), but not of lipids such as lactosylceramide (LacCer), dodecasaccharideceramine (DoCer), galactosylceramide (GalCer), ceramide (Cer), or the ganglioside GM1. Apart from germinal center B cells, normal tissues are Gb3 membrane-negative. Co-localization off Hsp70 and Gb3 was selectively determined in Gb3 membrane-positive tumor cells, and these cells were also shown to bind soluble Hsp70-FITC protein from outside in a concentration-dependent manner. Given that the latter interaction can be blocked by a Gb3-specific antibody, and that the depletion og globotriaosides from tumors reduces the amount of membrane-bound Hsp70, we propose that Gb3 is a binding partner for Hsp70. The in vitro finding that Hsp70 predominantly binds to artificial liposomes containing Gb3 (PC/SM/chol/Gb3, 17/45/33/5) confirms thaty Gb3 is an interaction partners for Hsp70. Conclusions/Significance: These data indicate that the presence of Gb3 enables anchorage of Hsp70 in the plasma membrane of tumors and thus they might explain tumor-specific membrane localization of Hsp70.