[68]

THE EFFECT OF MICROGRAVITY ON CYTOSKELETON ARCHITECTURE AND PROLIFERATION OF HUMAN BREAST CANCER CELL LINE MCF-7.    J Vassy¹, S Portet¹, D Schoevaert¹, M Beil², G Millot¹, G Gasset³ and F Fauvel-Lafиve¹.  ¹IUH Saint Louis, Paris, France; ²Universitдtsklinikum, Ulm, Germany; and ³GSBM, Toulouse, France.

As cells are sensitive to mechanical forces, microgravity might act on stress-dependent cell changes. We proposed that the integration of environmental factors might induce specific cytoskeletal architecture patterns. The latter were characterized by quantitative image analysis.

The human breast cancer cells MCF-7 were flown on a Photon capsule. Cells were fixed in a paraformaldehyde glutaraldehyde mixture after 1.30, 22 and 48 h in orbit. 1g in flight controls were compared to microgravity experiments.

Postflight, immunofluorescent localizations were performed to visualize cell proliferation (Ki67), signal transduction (phosphotyrosine), microtubules and intermediate filaments (cytokeratins). Microfilaments were visualized using fluorescent phalloidin and DNA using chromomycin A₃. Confocal microscopy and image analysis were used to quantify the number of proliferating cells and mitosis, the modifications of cytokeratin networks and chromatin texture.

In microgravity, phosphotyrosine signal transduction were reduced and number of proliferating cells were increased in correlation with mitosis. Numerous cells showed diffuse microtubules. Perinuclear cytokeratin networks were relaxed and chromatin texture modified.

In conclusion, the increase of the mitosis period can be explained by an alteration of the microtubule self-assembly in microgravity, involving reaction-diffusion processes. Relaxation of perinuclear cytokeratin network and modification of chromatin distribution are in agreement with basic predictions of cellular tensegrity.