MITOGEN-ACTIVATED PROTEIN-KINASE AND CYTOSKELETON IN MITOGENIC SIGNAL-TRANSDUCTION

This chapter highlights growth factor (GF)-induced actin cytoskeletal reorganization and the possible functions of cytoplasmic microtubules (MTs) in a GF-signaling pathway. It also focuses on the identification, properties, activation mechanism, and functions of mitogen-activated protein (MAP) kinase. The GF stimulation of cells triggers a variety of cascades of biochemical and physiological reactions in cells, thereby resulting in the entry into S phase, which is the initiation of DNA synthesis. The cytoskeleton comprises MTs, actin filaments, and intermediate filaments. These three types of protein filaments exist in the cytoplasm, outside nucleus, and inside the cell. Actin filaments and cytoplasmic MTs are dynamic in nature, and the turnover or exchange of the subunit proteins in polymers occurs rapidly in every phase of the cell cycle. These structures play roles in determining not only the cell shape but also in the localization and orientation of intracellular organelles. MAP kinase is a serine or threonine-specific protein kinase, the activation and phosphorylation of which are induced by a variety of mitogens. MAP kinase can utilize MAP (microtubule-associated protein) 2, which is one of the best known MT-associated proteins and an excellent substrate in vitro. © 1992, Academic Press Inc.