DETECTION OF PROTEIN-KINASE ACTIVITY SPECIFICALLY ACTIVATED AT METAPHASE ANAPHASE TRANSITION

We have previously reported that Ser13 and Ser34 on glial fibrillary a cidic protein (GFAP) in the cleavage furrow of glioma cells are phosph orylated during late mitotic phase (Matsuoka, Y., K. Nishizawa, T. Yan o, M. Shibata, S. Ando, T. Takahashi, and M. Inagaki. 1992. EMBO (Eur. Mol. Biol. Organ.) J. 11:2895-2902). This observation implies a possi bility that there is a protein kinase specifically activated at metaph ase-anaphase transition. To further analyze the cell cycle-dependent G FAP phosphorylation, we prepared monoclonal antibodies KT13 and KT34 w hich recognize the phosphorylation of GFAP at Ser13 and Ser34, respect ively. Immunocytochemical studies with KT13 and KT34 revealed that the GFAP phosphorylation in the cleavage furrow during late mitotic phase occurred not only in glioma cells but also in human SW-13 and mouse L tk(-) cells in which GFAP was ectopically expressed, thus the phosphor ylation can be monitored in a wide range of cell types. Furthermore, w e detected kinase activity which phosphorylates GFAP at Ser13 and Ser3 4 in the lysates of late mitotic cells but not in those of interphase cells or early mitotic cells. These results suggest that there exists a protein kinase which is specifically activated at the transition of metaphase to anaphase not only in GFAP-expressing cells but also in ce lls without GFAP.