PHOSPHOTYROSINE-DEPENDENT TARGETING OF MITOGEN-ACTIVATED PROTEIN-KINASE IN DIFFERENTIATED CONTRACTILE VASCULAR CELLS

Tyrosine phosphorylation has been linked to plasmalemmal targeting of src homology-2-containing proteins, activation of mitogen-activated pr otein (MAP) kinase, nuclear signaling, and proliferation of cultured c ells. Significant tyrosine phosphorylation and MAP kinase activities h ave also been reported in differentiated cells, but the signaling role of tyrosine-phosphorylated MAP kinase in these cells is unclear. The spatial and temporal relation between phosphotyrosine and MAP kinase i mmunoreactivity was quantified in differentiated contractile vascular smooth muscle cells by using digital imaging microscopy. An initial as sociation of MAP kinase with the plasmalemma required upstream protein kinase C activity but occurred in a tyrosine phosphorylation-independ ent manner. Subsequent to membrane association, a delayed redistributi on of MAP kinase, colocalizing with the actin-binding protein caldesmo n, occurred in a tyrosine phosphorylation-dependent manner. The appare nt association of MAP kinase with the contractile proteins coincided w ith contractile activation. Thus, tyrosine phosphorylation appears to target MAP kinase to cytoskeletal proteins in contractile vascular cel ls. This targeting mechanism may determine the specific destination an d thereby the specialized function of MAP kinase in other phenotypes.