Dual function of membrane-bound heat shock protein 70 (Hsp70), Bag-4, and Hsp40: protection against radiation-induced effects and target structure for natural killer cells

Cell Death Differ. 2005 Jan;12(1):38-51. doi: 10.1038/sj.cdd.4401510.


CX+/CX- and Colo+/Colo- tumor sublines with stable heat shock protein 70 (Hsp70) high and low membrane expression were generated by fluorescence activated cell sorting of the parental human colon (CX2) and pancreas (Colo357) carcinoma cell lines, using an Hsp70-specific antibody. Two-parameter flow cytometry revealed that Hsp70 colocalizes with Bag-4, also termed silencer of death domain, not only in the cytosol but also on the plasma membrane. After nonlethal gamma-irradiation, the percentage of membrane-positive cells and the protein density of Hsp70 and Bag-4 were found to be strongly upregulated in carcinoma sublines with initially low expression levels (CX-, Colo-). Membrane expression of Hsp70 was also elevated in Bag-4 overexpressing HeLa cervix carcinoma cells when compared to neo-transfected cells. In response to gamma-irradiation, neo-transfected HeLa cells behaved like Hsp70/Bag-4 low-expressing CX- and Colo-, and Bag-4-transfected HeLa cells like Hsp70/Bag-4 high-expressing carcinoma sublines CX+ and Colo+. Immunoprecipitation studies further confirmed colocalization of Hsp70 and Bag-4 but also point to an association of Hsp70 and Hsp40 on the plasma membrane of CX+ and Colo+ cells; on CX- and Colo- tumor sublines, Hsp40 was detectable in the absence of Hsp70 and Bag-4. Other co-chaperones including Hsp60 and Hsp90 were neither found on the cell surface of CX+/CX-, Colo+/Colo- nor on HeLa neo-/HeLa Bag-4-transfected tumor cells. Functionally, Hsp70/Bag-4 and Hsp70/Hsp40 membrane-positive tumor cells appeared to be better protected against radiation-induced effects, including G2/M arrest and growth inhibition, on the one hand. On the other hand, membrane-bound Hsp70, but neither Bag-4 nor Hsp40, served as a recognition site for the cytolytic attack mediated by natural killer cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / genetics
  • Adaptor Proteins, Signal Transducing / metabolism
  • Adaptor Proteins, Signal Transducing / physiology
  • Apoptosis / radiation effects
  • Cell Cycle / radiation effects
  • Cell Line, Tumor
  • Cell Proliferation / radiation effects
  • Cell Survival / radiation effects
  • Colonic Neoplasms / pathology
  • Cytotoxicity, Immunologic / immunology
  • Cytotoxicity, Immunologic / radiation effects
  • Gamma Rays
  • Gene Expression / radiation effects
  • HSP40 Heat-Shock Proteins
  • HSP70 Heat-Shock Proteins / immunology
  • HSP70 Heat-Shock Proteins / metabolism
  • HSP70 Heat-Shock Proteins / physiology
  • HeLa Cells
  • Heat-Shock Proteins / metabolism
  • Heat-Shock Proteins / physiology
  • Humans
  • Killer Cells, Natural / immunology
  • Killer Cells, Natural / physiology*
  • Killer Cells, Natural / radiation effects
  • Membrane Proteins / immunology
  • Membrane Proteins / metabolism
  • Membrane Proteins / physiology*
  • Radiation Tolerance / physiology*
  • Transfection
  • Up-Regulation


  • Adaptor Proteins, Signal Transducing
  • BAG4 protein, human
  • DNAJB1 protein, human
  • HSP40 Heat-Shock Proteins
  • HSP70 Heat-Shock Proteins
  • Heat-Shock Proteins
  • Membrane Proteins