抄録
How physical force is sensed by cells and transduced into cellular signaling is poorly understood. When we found that phosphorylation of p130Cas (Cas) was involved in a physiological force transduction, we postulated four possible mechanisms of stretch-dependent tyrosine phosphorylation of Cas: 1) Kinase (Src family kinase) is activated by stretching, 2) Phosphatase of Cas is inactivated by stretching, 3) Kinase and substrate (Cas) spatially interact upon stretching, 4) Susceptibility of Cas to phosphorylation is enhanced by stretching. Because our experimental data suggested that mechanisms 1)–3) were not primarily responsible for the stretch-dependent phosphorylation of Cas, we tested the possibility 4). To eliminate any extraneous biochemical interactions or signaling pathways, we constructed an in vitro protein extension system in which bacterially expressed Cas substrate domain proteins (CasSD) were extended and analyzed biochemically. We found that mechanical extension of CasSD enhanced its tyrosine phosphorylation by c-Src kinase with no apparent change in Src kinase activity in vitro. Physiological relevance of in vitro CasSD extension was confirmed by immunostaining intact cells fixed in the late phase of spreading using an extension-specific anti-Cas antibody. Thus, Cas converts force into a biochemical signal through mechanical extension of its substrate domain, causing priming to phosphorylation. We propose such "substrate priming" is a general mechanism regulating intracellular signal transduction. [J Physiol Sci. 2007;57 Suppl:S28]
