The major stress-inducible protein Hsp70 (HSPA1A) is overexpressed in the cytosol of many highly aggressive tumor cells including glioblastoma multiforme and presented on their plasma membrane. Depending on its intracellular or membrane localization, Hsp70 either promotes tumor growth or serves as a target for natural killer (NK) cells. The kinetics of the membrane Hsp70 (mHsp70) density on human glioma cells (U87) was studied after different irradiation doses to define the optimal therapeutic window for Hsp70-targeting NK cells. To maintain the cells in the exponential growth phase during a cultivation period of 7 days, different initial cell counts were seeded. Although cytosolic Hsp70 levels remained unchanged on days 4 and 7 after a sublethal irradiation with 2, 4 and 6 Gy, a dose of 2 Gy resulted in an upregulated mHsp70 density in U87 cells which peaked on day 4 and started to decline on day 7. Higher radiation doses (4 Gy, 6 Gy) resulted in an earlier and more rapid onset of the mHsp70 expression on days 2 and 1, respectively, followed by a decline on day 5. Membrane Hsp70 levels were higher on cells in G2/M than in G1; however, an irradiation-induced cell cycle arrest on days 4 and 7 was not associated with an increase in the mHsp70 density. Extracellular Hsp70 concentrations in the supernatant of irradiated cells were significantly higher than sham (0 Gy) irradiated cells on days 4 and 7, but not on day 1. Functionally, elevated mHsp70 densities were associated with a significantly better lysis by Hsp70-targeting NK cells. In summary, the kinetics of changes in the mHsp70 density upon irradiation on tumor cells is time- and dose-dependent.

The major stress-inducible 70 kDa heat shock (stress) protein 70 (Hsp70) is frequently overexpressed in highly aggressive tumor cells and thus might serve as a tumor-specific biomarker of aggressive disease. We have previously shown that, in contrast to normal cells, tumor cells present Hsp70 on their plasma membrane. In order to elucidate the role of intracellular and membrane-bound Hsp70 as a potential tumor biomarker in glioblastoma multiforme, herein, we describe protocols for the staining of cytosolic Hsp70 in tumor formalin fixed paraffin-embedded (FFPE) sections using immunohistochemistry, and for plasma membrane-bound Hsp70 by multi-parametric flow cytometry using the cmHsp70.1 monoclonal antibody (mAb).

The major stress-inducible Hsp70 (HSPA1A) is overexpressed in the cytosol of many highly aggressive tumor cells including glioblastoma multiforme and presented on their plasma membrane. Depending on its intracellular or membrane localization, Hsp70 either promotes tumor growth or serves as a target for NK cells. The kinetics of the membrane Hsp70 (mHsp70) density on human glioma cells (U87) was studied after different irradiation doses to define the optimal therapeutic window for Hsp70-targeting NK cells. To maintain the cells in the exponential growth phase during a cultivation period of 7 days different initial cell counts were seeded. Although cytosolic Hsp70 levels remained unchanged on days 4 and 7 after a sublethal irradiation with 2 Gy, 4 Gy and 6 Gy, a dose of 2 Gy resulted in an upregulated mHsp70 density in U87 cells which peaks on day 4 and starts to decline on day 7. Higher radiation doses (4 Gy, 6 Gy) resulted in an earlier and more rapid onset of the mHsp70 expression on days 2 and 1, respectively, followed by a decline on day 5. Membrane Hsp70 levels are higher in G2/M than in G1, however, an irradiation-induced cell cycle arrest on days 4 and 7, was not associated with an increase in the mHsp70 density. Extracellular Hsp70 concentrations increased significantly compared to sham (0 Gy) irradiated cells on days 4 and 7 but not on day 1. Functionally, elevated mHsp70 densities were associated with a significantly better lysis by Hsp70-targeting NK cells. In summary, the kinetics of changes in the mHsp70 density upon irradiation on tumor cells is time- and dose-dependent.

The major stress-inducible Hsp70 (HSPA1A) is overexpressed in highly aggressive tumor cells including glioblastoma multiforme and presented on their plasma membrane. Ionizing irradiation increases cytosolic and membrane-bound Hsp70 (mHsp70) on tumor cells. Depending on its intracellular or membrane localization, Hsp70 either promotes tumor growth or serves as a target for the innate immune system. To define the optimal window for a therapy with Hsp70-tageting NK cells the kinetics of the mHsp70 density on the plasma membrane of human glioma cells (U87) has been studied after radiotherapy by multiparameter flow cytometry. Cell cycle dependent alterations in the mHsp70 expression were excluded by seeding different cell numbers on day 0. Low dose irradiation (2 Gy) results in a slow upregulation of the mHsp70 density in U87 cells which peaks on day 4 and starts to decline from day 7 onwards. In contrast, higher radiation doses (4 Gy, 6 Gy) resulted in a faster upregulation of mHsp70 expression on days 2 and 1, respectively, followed by a decline from day 5 onwards. Functionally, elevated mHsp70 densities correlate with an improved lysis by Hsp70-targeting NK cells. In summary, the kinetics of changes in the mHsp70 density upon irradiation on tumor cells is time and dose-dependent.