Role of cytoskeletal proteins phosphorylation on their cellular functions.

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Phosphorylation and dephosphorylation of proteins dynamically alter the structure and function of proteins and are regarded as a form of an on/off switch regulating various vital phenomena. If the phosphorylation and dephosphorylation of proteins could be visualized, especially in terms of the distribution, site and transition of each reaction, the relevant and various vital phenomena, that currently can be investigated merily by indirect means, might be more revealing. Based on this concept, we prepared a group of antibodies that can identify whether a cytoskeletal protein is phosphorylated or dephosphorylated.We developed four antibodies which distinguish phosphorylated states of Thr7, Ser8, Ser13 and Ser34 in glial fibrillary acidic protein (GFAP), a protein constituted of glial filaments of astroglial cells. Immunofluorescence microscopy shows that Ser8 residues in all cytoplasmic glial filaments are initially phosphorylated when the astroglial cells enter mitosis. In cytokinesis, the phospho-Ser8 residues become dephosphorylated, whereas Thr7, Ser13 and Ser34 in the filaments at the cleavage furrow become the preferred sites of phosphorylation.Such being the case, at least two different types of protein kinases act as mitotic glial filament kinases, at a different time schedule during mitosis. A phosphatase (s) acts as a mitotic glial filament phosphatase, at the time of meta-anaphase transition.