CELL-CYCLE DEPENDENT REGULATION OF THE PROTEIN-KINASE TTK

TTK is a novel protein kinase detectable in all proliferating human ce lls and tissues. Expression of the TTK gene is markedly reduced or abs ent in resting cells and in tissues with a low proliferative index. In view of the apparent association between TTK gene expression and cell proliferation, we examined the regulation of this protein kinase duri ng transit of the cell cycle. We found very low levels of TTK mRNA and protein in starved cells. When cells are induced to enter the cell cy cle, levels of TTK mRNA, protein and kinase activity increase at the G 1/S phase of the cell cycle and peak in G2/M. TTK mRNA levels, as well as kinase activity, drop sharply in early G1, whereas protein levels are largely maintained. TTK may play a role in cell cycle control.