Effects of hyperthermia on the cytoskeleton and cell survival in G1 and S phase Chinese hamster ovary cells

Abstract

The effects of acute hyperthermia on three cytoskeletal systems (microtubules (MT), microfilaments (MF), and vimentin intermediate filaments (VIMF] were observed in G1 and S phase Chinese hamster ovary (CHO) 10B cells using immunofluorescence microscopy and compared to cell survival. A scoring system was devised to express the degree of cytoskeletal collapse induced by heat and the degree of recovery 20 h following heat treatments. A positive correlation was found between recovery from heat-induced cytoskeletal disruption and surviving fractions (SF) of cells heated in G1 but not with SF of cells heated in S phase. Recovery of MT arrays, for example, averaged 96.5%, 71.6% and 20.3% for heat doses of 5 min, 15 min and 25 min, 45 degrees C, respectively. The corresponding SF (means) were 0.92, 0.68 and 0.23, respectively. However, in S phase cells, where restoration of MT and VIMF patterns averaged 94.2%, 83.8% and 33.0% for heat doses of 5 min, 15 min and 25 min, 45 degrees C respectively, SF were 0.70, 0.09 and 0.02. These results suggest that heat-induced cytoskeletal alterations may play a role in the death of cells heated in G1, and that these alterations do not significantly influence death of cells heated in S phase. This work is in agreement with previous studies showing that cells heated in G1 or S phase appear to die by different mechanisms, and further emphasizes the need to use synchronous populations of cells in order to understand the mechanisms whereby cells die following hyperthermia.