INDUCTION OF CYCLIN-B AND H1 KINASE-ACTIVITY IN APOPTOTIC PC12 CELLS

The present study examines whether cyclin B may be involved in apoptosis of neuronally differentiated PC12 cells following withdrawal of NGF. Cyclin B mRNA increased approximately 10-fold 4 days after NGF withdrawal, as indicated by competitive RT/PCR. Sequencing of the PCR product confirmed that it was derived from cyclin B mRNA cyclin B protein increased in parallel with cyclin B mRNA, as shown by immunoblotting. Immunoprecipitation with anti-cyclin B antibody demonstrated that cyclin B was associated with H1K activity, which reached a maximum 5 days after NGF withdrawal. When proteins immunoprecipitated with anti-cyclin B antibody were immunoblotted with anti-PSTAIR antibody, a protein with apparent molecular weight of 34 kDa was detected. This protein was identified as p34(cdc2) On the basis of immunoreactivity with antibody against the C-terminal portion of mouse p34(cdc2). Since cyclin B/p34(cdc2) complexes are known to catalyze chromosomal condensation and nuclear envelope breakdown during mitosis, these results suggest that cyclin B/p34(cdc2) may play some role in the nuclear changes accompanying apoptosis of PC12 cells. (C) 1995 Academic Press, Inc.