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°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°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.

Key Words:

• Hyperthermia
• cytoskeleton
• synchronous CHO cells
• cytotoxicity