Matsuoka Y, Nishizawa K, Yano T, Shibata M, Ando S, Takahashi T, Inagaki M
Laboratory of Experimental Radiology, Aichi Cancer Center Research Institute, Japan.
EMBO J. 1992 Aug;11(8):2895-902. doi: 10.1002/j.1460-2075.1992.tb05358.x.
Glial fibrillary acidic protein (GFAP) is a component of glial filaments specific to astroglia. We now report the spatial and temporal distributions of four phosphorylated sites in the GFAP molecule during mitosis of astroglial cells, determined by antibodies which can distinguish phosphorylated epitopes from non-phosphorylated-epitopes. Immunofluorescence microscopy showed that the Ser8 residues in the entire cytoplasmic glial filament system are initially phosphorylated when the cells enter mitosis. In cytokinesis, the phosphoSer8 residues become dephosphorylated, whereas Thr7, Ser13 and Ser34 in glial filaments at the cleavage furrow become the preferred sites of phosphorylation. The cdc2 kinase purified from mitotic cells can phosphorylate GFAP at Ser8 but not at Thr7, Ser13 or Ser34, in vitro. These results suggest that cdc2 kinase acts as a glial filament kinase only at the G2-M phase transition while other glial filament kinases are probably activated at the cleavage furrow before final separation of the daughter cells.
胶质纤维酸性蛋白（GFAP）是星形胶质细胞特有的胶质丝的一个组成部分。我们现在报告在星形胶质细胞有丝分裂期间GFAP分子中四个磷酸化位点的时空分布，这是通过能够区分磷酸化表位和非磷酸化表位的抗体来确定的。免疫荧光显微镜显示，当细胞进入有丝分裂时，整个细胞质胶质丝系统中的Ser8残基首先被磷酸化。在胞质分裂过程中，磷酸化的Ser8残基去磷酸化，而在分裂沟处的胶质丝中的Thr7、Ser13和Ser34成为优先磷酸化位点。从有丝分裂细胞中纯化的cdc2激酶在体外可使GFAP的Ser8磷酸化，但不能使Thr7、Ser13或Ser34磷酸化。这些结果表明，cdc2激酶仅在G2-M期转换时作为胶质丝激酶起作用，而其他胶质丝激酶可能在子细胞最终分离前在分裂沟处被激活。
