Effect of weightlessness on cytoskeleton architecture and proliferation of human breast cancer cell line MCF‐7

Because cells are sensitive to mechanical forces, weightlessness might act on stress‐dependent cell changes. We hypothesized that the integration of environmental factors might induce specific cytoskeletal architecture patterns, characterized by quantitative image analysis. Human breast cancer cells MCF‐7, flown in space in a photon capsule, were fixed after 1.5, 22, and 48 h in orbit. Cells subjected to weightlessness were compared with 1 g in‐flight and ground controls. Postflight, fluorescent labelings were performed to visualize cell proliferation (Ki‐67), signal transduction (phosphotyrosine), three cytoskeleton components (microtubules, microfilaments, and intermediate filaments), and chromatin structure. Confocal microscopy and image analysis were used to quantify cycling cells and mitosis, modifications of the cytokeratin network, and chromatin structure. In weightlessness, phosphotyrosine signal transduction was lower, more cells were cycling, and mitosis was prolonged. Finally, cell proliferation was reduced as a consequence of a cell‐cycle blockade. Microtubules were altered in many cells. The perinuclear cytokeratin network was more loosely ‘woven’, and chromatin structure was modified. The prolongaion of mitosis can be explained by an alteration of microtubule self‐organization in weightlessness, involving reaction‐diffusion processes. The loosening of the perinuclear cytokeratin network and modification of chromatin distribution are in agreement with basic predictions of cellular tensegrity.