Signal transduction and cytoskeletal reorganization are required for cell detachment from cell culture surfaces grafted with a temperature-responsive polymer.

We have developed a new cell culture substrate grafted with a temperature-responsive polymer, poly(N-isopropylacrylamide) (PIPAAm) using an electron beam irradiation method. These surfaces are hydrophobic in culture at 37 degrees C due to the hydration/dehydration changes intrinsic to PIPAAm at 32 degrees C, and they become highly hydrophilic below 32 degrees C. At 37 degrees C grafted and ungrafted surfaces showed no difference with regard to attachment, spreading, growth, confluent cell density, and morphology of bovine aortic endothelial cells. Stress fibers, peripheral bands, and focal contacts were established in similar ways. After the medium temperature was decreased to 20 degrees C, spread cells lost their flattened morphology, acquiring a rounded cell appearance similar to that of cells immediately after plating. After mild agitation cells floated free from the dish surface without trypsin treatment. Neither cell morphological changes nor cell detachment occurred on ungrafted surfaces. An ATP synthesis inhibitor, sodium azide, and a tyrosine kinase inhibitor, genistein, suppressed cell morphological changes and cell detachment while a protein synthesis inhibitor, cycloheximide, slightly enhanced cell detachment. An actin filament stabilizer, phalloidin, and its depolymerizer, cytochalasin D, also inhibited cell detachment. These findings suggest that cell detachment on grafted surfaces is mediated by intracellular signal transduction and reorganization of the cytoskeleton. While trypsinization causes damage to the cell membrane surface and extracellular matrix proteins, this alternative low temperature treatment is exceptionally noninvasive. The temperature-responsive cell culture surface also should prove useful for investigating the molecular machinery involved in cell-surface detachment.