HSP70: Protein Type

HSP70s are monomeric proteins that reside in the cytosol of prokaryotes and the cytosol, nuclei, ER, mitochondria and chloroplasts of eukaryotes ⁸. In addition to their intracellular location, HSP70s have been found in the plasma membrane of malignantly transformed cells, on virally / bacterially infected cells and in the extracellular space. Extracellular Hsp70 exists in a free soluble form, complexed to antigenic peptides, or in exosomes ^12,13,14,15. Noteworthy, Hsp70-1 as the most prominent member of the HSP70 family can be detected in the plasma membrane of a large proportion of different tumor entities, but not in the plasma membrane of normal cells/tissues ^16,17,18. Several observations have led to the hypothesis that in tumor cells Hsp70-1 is an integral membrane protein associated with certain membrane lipid components ^{15, 16}.