EPIDERMAL GROWTH-FACTOR RAPIDLY IMPAIRS ACTIVATION OF P34(CDC2) PROTEIN-KINASE IN HELA-CELLS AT THE G2-M BOUNDARY

Epidermal growth factor (EGF) has been shown rapidly to inhibit the tr ansition from G2 phase to mitosis; beyond this transition point the ce lls are refractory to EGF (Kinzel et al., 1990, Cancer Res., 50:7932-7 936). Using synchronized HeLa cells, EGF has now been shown to induce an overall decrease of the histone H1 kinase activity of p34(cdc2) aft er 20 min of treatment, a time course which correlates with the number of cells in metaphase. The kinase level of actively mitotic cells is not altered by EGF. Neither the amount of p34(cdc2) protein present no r that of Cyclin B is influenced by EGF, and the formation of the p34( cdc2)/Cyclin B complex is also unaffected. The use of antiphosphotyros ine antibodies, however, showed that p34(cdc2) from cultures treated w ith EGF was more intensely stained than that of control cells, indicat ing that EGF treatment prevents the tyrosine dephosphorylation which i s required for expression of the protein kinase activity of the comple x. Taken together, the results show that EGF in HeLa cells very rapidl y prevents the p34(cdc2)/Cyclin B complex from expressing kinase activ ity at the G2-M boundary, which appears to be the cause for the inhibi tion in G2 phase. (C) 1995 Wiley-Liss, Inc.