HSP70

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}.

Fig 1: Ribbon and tube representation of the tertiary Hsp70-1 structure in the presence of ADP.

Heat shock proteins (HSPs) were originally described in the early 1960s by the pioneering work of Ferruccio Ritossa on the fruit fly Drosophila melanogaster ^5,6,7. Expression of HSPs was found as being induced after exposure to different kinds of stress such as heat shock and could be demonstrated subsequently in any cellular organism ⁸. Nevertheless, other stress conditions, including heavy metals, hypoxia, nutrient deprivation and irradiation as well as oxidative and toxic stress, infections and exposure to inflammatory cytokines are also able to induce HSP expression ^{8, 9}. Members of the HSP70 family were identified for the first time as being upregulated in bacteria in response to cellular stress ¹⁰. The painstaking analysis of the limited number of proteins firstly identified by heat shock induction in D. melanogaster and in E. coli led to the finding that DnaK, DnaJ and GrpE were also members of the heat shock class of proteins. In 1984, Bardwell and Craig demonstrated that the E. coli DnaK and the Drosophila 70 kDa heat shock proteins were highly conserved at the sequence level ¹¹. Moreover, hybridization between the DNA of the archaebacterium Methanosarcina barkeri and the HSP70 genes of D. melanogaster, Saccharomyces cerevisiae, and E. coli has been detected, suggesting the existence of Hsp70-related genes in the three “primary kingdoms”: eukaryotes, eubacteria, and archaebacteria¹¹.

The HSP70 Family

The HSP70 family represents the most conserved and best characterized group of HSPs comprising polypeptides whose molecular weights range from 66 – 78 kDa and that are encoded by a multigene family encompassing up to 17 genes and 30 pseudogenes in humans ¹⁹. Functional genes encoding HSP70 proteins map to human chromosomes 6, 14, 21, and at least one other chromosome ²⁰. The most studied genes are HSPA1A and HSPA1B encoding proteins that only differ by two amino acids and are believed as being completely interchangeable proteins. The genes are clustered in the major histocompatibility complex class III region on chromosome 6p21.3.

The HSP70 family constitutes one of the most conserved protein families in evolution. Their members are present in all organisms and subcellular compartments and can be found from archaebacteria and plants to humans. In archaea and eubacteria Hsp70 is referred to as DnaK. In yeasts they are called Ssa, in mammals including humans they are referred to as HspA.

More information is available on the HSP70 website
and antibodies and related products are available by searching on the Newmarket Scientific website.

References:
1. Gribaldo,S. et al. Discontinuous occurrence of the hsp70 (dnaK) gene among Archaea and sequence features of HSP70 suggest a novel outlook on phylogenies inferred from this protein. J. Bacteriol.181, 434-443 (1999). [PubMed]

2. Sharma,D. & Masison,D.C. Hsp70 structure, function, regulation and influence on yeast prions. Protein Pept. Lett.16, 571-581 (2009). [PubMed]

3. Sharma,D. et al. Function of SSA subfamily of Hsp70 within and across species varies widely in complementing Saccharomyces cerevisiae cell growth and prion propagation. PLoS. ONE.4, e6644 (2009). [PubMed]

4. Kampinga,H.H. & Craig,E.A. The HSP70 chaperone machinery: J proteins as drivers of functional specificity. Nat. Rev. Mol. Cell Biol.11, 579-592 (2010). [PubMed]

5. Ritossa,F. Experimental activation of specific loci in polytene chromosomes of Drosophila. Exp. Cell Res.35, 601-607 (1963). DOI: 10.1016/0014-4827(64)90147-8

6. Ritossa,F. New puffs induced by temperature shock, DNP and salicilate in salivary chromosomes of D. melanogaster. Drosophila Information Service37, 122-123 (1963). [Drosophila Information Service]

7. Ritossa,F. A new puffing pattern induced by temperature shock and DNP in Drosophila. Experientia18, 571-573 (1962). DOI: 10.1007/BF02172188

8. Lindquist,S. & Craig,E.A. The heat-shock proteins. Annu. Rev. Genet.22, 631-677 (1988). [PubMed]

9. Jäättelä,M. Heat shock proteins as cellular lifeguards. Ann. Med.31, 261-271 (1999). [PubMed]

10. Craig,E.A. & Gross,C.A. Is hsp70 the cellular thermometer? Trends Biochem. Sci.16, 135-140 (1991). [PubMed]

11. Bardwell,J.C. & Craig,E.A. Major heat shock gene of Drosophila and the Escherichia coli heat-inducible dnaK gene are homologous. Proc. Natl. Acad. Sci. U. S. A81, 848-852 (1984). [PubMed]

12. Bausero,M.A., Gastpar,R., Multhoff,G., & Asea,A. Alternative mechanism by which IFN-gamma enhances tumor recognition: active release of heat shock protein 72. J. Immunol.175, 2900-2912 (2005). [PubMed]

13. Gastpar,R. et al. Heat shock protein 70 surface-positive tumor exosomes stimulate migratory and cytolytic activity of natural killer cells. Cancer Res.65, 5238-5247 (2005). [PubMed]

14. Lancaster,G.I. & Febbraio,M.A. Exosome-dependent trafficking of HSP70: a novel secretory pathway for cellular stress proteins. J. Biol. Chem.280, 23349-23355 (2005). [PubMed]

15. Vega,V.L. et al. Hsp70 translocates into the plasma membrane after stress and is released into the extracellular environment in a membrane-associated form that activates macrophages. J. Immunol.180, 4299-4307 (2008). [PubMed]

16. Gehrmann,M. et al. Tumor-specific Hsp70 plasma membrane localization is enabled by the glycosphingolipid Gb3. PLoS. ONE.3, e1925 (2008). [PubMed]

17. Schilling,D. et al. Binding of heat shock protein 70 to extracellular phosphatidylserine promotes killing of normoxic and hypoxic tumor cells. FASEB J.23, 2467-2477 (2009). [PubMed]

18. Stangl,S. et al. Targeting membrane heat-shock protein 70 (Hsp70) on tumors by cmHsp70.1 antibody. Proc. Natl. Acad. Sci. U. S. A108, 733-738 (2011). [PubMed]

19. Brocchieri,L., Conway de,M.E., & Macario,A.J. hsp70 genes in the human genome: Conservation and differentiation patterns predict a wide array of overlapping and specialized functions. BMC. Evol. Biol.8, 19 (2008). [PubMed]

20. Harrison,G.S. et al. Chromosomal location of human genes encoding major heat-shock protein HSP70. Somat. Cell Mol. Genet.13, 119-130 (1987). [PubMed]