28. ONCOGENIC ras RESULTS IN INCREASED CELL KILL DUE TO DEFECTIVE THERMOPROTECTION IN LUNG CANCER CELLS SUBJECTED TO HEAT STRESS

Roger A. Vertrees, Paul J. Boor and Joseph B. Zwischenberger

Departments of Surgery and Pathology, University of Texas Medical Branch

Galveston, Texas, USA

Heat stress causes an upregulation of heat shock proteins [inducing thermoprotection against initial heat (thermoresistance) and subsequent heat insults (thermotolerance)], and Ras activation (resulting in apoptotic cell death, when thermoprotection is overwhelmed). We hypothesized, oncogenic ras, found in many lung cancers, interferes with thermoprotection.

Human cell lines: normal, CCD-19LU, BEAS2-B, WI-38; and malignant, NCIH82, S₃D₃, LB9, L27, BZR, BZR-T33 were subjected to either heat (43 degrees Celsius for 180 min) then (37 degrees Celsius for 180 min) or to sham (37 degrees Celsius for 360 min). Cells were counted by Coulter counter then percent cells apoptotic (Hoechst stain) and time course of HSP70 expression (Western blot) were measured in normal (BEAS2-B) and malignant (BZR-T33) cells.

Normal cell lines, cell death: CCD-19LU 0%, WI-38 0% and BEAS2-B 8%, with an 8% increase in apoptosis. HSP70 showed an immediate increase (100-fold at 2 h) HSP70, elevated but decreasing at 24 h. Malignant cells, cell death: L27 61%, LB9 75%, BZR-T33 56%, with a 53% increase in apoptosis. HSP70 had a delayed increase (50-fold at 5 h) but decreasing at 24 h.

Malignant lung cells are more thermosensitive than normal lung cells with defective thermoprotective mechanisms, which may impart a therapeutic window for treatment.