TYROSINE PHOSPHORYLATION OF 40 KDA PROTEINS IN OSTEOBLASTIC CELLS AFTER MECHANICAL STIMULATION OF BETA(1)-INTEGRINS

Using a method for the mechanical stimulation of cells which was adapt ed from one developed by Wang and Ingber employing magnetic microbeads [Wang, N. D., D. E. Ingber: Control of cytoskeletal mechanics by extr acellular matrix, cell shape, and mechanical tension, Biophys, J. 66, 2181-2189 (1994)], mechanical stress could be applied to specific rece ptors on the cell surface. To achieve this, ferromagnetic microbeads c oated with different ligands were magnetized after adhesion to the cel ls, The beads were then 'twisted' using a second magnetic field orient ed perpendicular to the magnetizing one, Contrary to most current meth ods, it was possible to confer the strain without deforming the cell a s a whole, thus being able to observe the individual reactions of tran smembrane receptors to mechanical stress. An increase in tyrosine phos phorylation of proteins migrating at approximately 40 kDa could be obs erved as a reaction to stress on the beta(1)-subunits of the integrin family, while stress to other transmembrane molecules like the transfe rrin or low density lipoprotein receptors with no connection to the cy toskeleton did not give this reaction, Fibroblastic cells showed, cont rary to osteoblastic cells, no reaction to stress applied on transmemb rane proteins.