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* Departments of Immunology and Vascular Biology, The Scripps Research Institute, La Jolla, California 92037; Cell interaction with adhesive proteins or
growth factors in the extracellular matrix initiates Ras/
mitogen-activated protein (MAP) kinase signaling. Evidence is provided that MAP kinase (ERK1 and ERK2)
influences the cells' motility machinery by phosphorylating and, thereby, enhancing myosin light chain kinase (MLCK) activity leading to phosphorylation of
myosin light chains (MLC). Inhibition of MAP kinase
activity causes decreased MLCK function, MLC phosphorylation, and cell migration on extracellular matrix
proteins. In contrast, expression of mutationally active
MAP kinase kinase causes activation of MAP kinase
leading to phosphorylation of MLCK and MLC and enhanced cell migration. In vitro results support these
findings since ERK-phosphorylated MLCK has an increased capacity to phosphorylate MLC and shows increased sensitivity to calmodulin. Thus, we define a signaling pathway directly downstream of MAP kinase,
influencing cell migration on the extracellular matrix.
Department of
Physiology and Biophysics, University of Illinois at Chicago, Chicago, Illinois 60612; and § Department of Physiology and
Biophysics, University of Indiana, School of Medicine, Indianapolis, Indiana 46202-5120
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