Tumor-Specific Hsp70 Plasma Membrane Localization Is Enabled by the Glycosphingolipid Gb3

Human tumors differ from normal tissues in their capacity to present Hsp70, the major stress-inducible member of the 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.Although Hsp70 has been reported to be associated with cholesterol rich microdomains (CRMs), the partner in the plasma membrane with which Hsp70 interacts has yet to be identified. Herein, global lipid profiling demonstrates that Hsp70 membrane-positive tumors differ from their membrane-negative counterparts by containing significantly higher amounts of globotriaoslyceramide (Gb3), but not of other lipids such as lactosylceramide (LacCer), dodecasaccharideceramide (DoCer), galactosylceramide (GalCer), ceramide (Cer), or the ganglioside GM1. Apart from germinal center B cells, normal tissues are Gb3 membrane-negative. Co-localization of 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 of 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 that Gb3 is an interaction partner for Hsp70.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

Expression of receptors for verotoxin 1 from <i>Escherichia coli</i> O157 on bovine intestinal epithelium.

Human enterohaemorrhagic &lt;i&gt;Escherichia coli&lt;/i&gt; (EHEC) infection most commonly arises, either directly or indirectly, from cattle, which act as a reservoir host for these bacteria. In man, EHEC disease can be severe, whereas EHEC do not normally cause disease in cattle. Verotoxins (VTs) are the main virulence factors in human disease but no role for VT has been ascribed in cattle; however, this study shows for the first time that VT receptor is expressed by the bovine intestinal tract. VT bound to crypt epithelial cells of the small (ileum and jejunum) and large (caecum and colon) intestine independently of the animals' age. VT also bound to discrete cell subsets in the bovine kidney and to submucosal lymphoid cells but not to vasculature. Analysis of tissues for isoforms of the VT receptor, Gb3, confirmed the presence of the receptor in the bovine intestinal epithelium and kidney. A distinct pattern of Gb3 receptor isoform mixtures was observed in the bovine kidney. This, together with the general absence of receptors on vasculature, could contribute to the apparent resistance of cattle to systemic effects of VT. Expression of Gb3 on the bovine intestinal epithelium, together with previously described effects, may affect EHEC colonisation in its reservoir hosts and hence the potential for distribution to man