PHOSPHORYLATION OF RETINOBLASTOMA PROTEIN AT APOPTOTIC CELL-DEATH IN RAT NEUROBLASTOMA B50 CELLS

Phosphorylation of the retinoblastoma protein (RB) was observed during apoptosis of B50 neuroblastoma cells following induction by dibutyryl cAMP, after differentiation into neurons, or by cycloheximide during proliferation. A weak but distinct increase in a RE and histone H1 kin ase activity was detected at the time of RE phosphorylation. However, the RE kinase appeared to correspond to neither p34(cdc2) kinase, CDK2 nor CDK5 because it was not inhibited by butyrolactone I, an inhibito r for them. Expression of CDK4 and 6 along with several cyclins also d id not coincide with the appearance of phosphorylated RE in the apopto tic process. (C) 1997 Elsevier Science ireland Ltd.