Bcl-xL overexpression restricts heat-induced apoptosis and influences hsp70, bcl-2, and Bax protein levels in FL5.12 cells.
Although several proteins have been identified that can inhibit stress-induced apoptosis, the cytoprotective potential of bcl-xL against heat shock and its ability to alter hsp70 induction is not known. The current study, using control and bcl-xL-overexpressing IL-3-dependent FL5.12 cells, compared the effects of 1 h of acute heat stress (42 degrees C) followed by 1, 4, and 8 h recovery (37 degrees C) on hsp70, bax, bcl-2, and bcl-xL protein levels and apoptosis. Less than 0.5% of untreated cells were apoptotic. There was significantly more apoptosis in control ( approximately 16%) as compared to bcl-xL cells ( approximately 3%) 8 h after heat stress. Immunoblotting revealed a time-dependent increase in hsp70 protein levels following 1 h of heat stress in control, but not bcl-xL-overexpressing cells. bcl-2 protein levels were lower in bcl-xL-overexpressing cells than in controls, but decreased in both cell lines after heat stress. bax protein levels in bcl-xL-overexpressing cells were decreased approximately 80% below baseline levels 1 h post heat shock. This decrease was maintained to 8 h. No change in bax protein was observed in control cells up to 8 h post heat shock. These data indicate that bcl-xL overexpression mitigates the effects of acute heat stress so that hsp70 induction is eliminated and apoptosis is prevented. The rapid loss of bax protein following heat stress in bcl-xL-overexpressing, but not control, cells may contribute to their resistance to apoptosis. Conversely, the loss of bcl-2 protein following heat stress in control cells may contribute to their susceptibility to apoptosis.
Robertson
J D
JD
College of Pharmacy, The University of Texas at Austin, Austin, Texas 78712-1074, USA. jdrobertson@mail.utexas.edu
Datta
K
K
Kehrer
J P
JP
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002460:Cell Line; D018840:HSP70 Heat-Shock Proteins / Q000096:biosynthesis*; D006412:Hematopoietic Stem Cells; D006358:Hot Temperature; D051379:Mice; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis* / Q000378:metabolism*; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D014162:Transfection; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
C494827:Bax protein, mouse; C494812:Bcl2l1 protein, mouse; D018840:HSP70 Heat-Shock Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011994:Recombinant Proteins; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein