INVOLVEMENT OF CDC2-MEDIATED PHOSPHORYLATION IN THE CELL CYCLE-DEPENDENT REGULATION OF P185(NEU)

We previously reported cell cycle-dependent negative regulation of p18 5(neu) (decreased tyrosine phosphorylation and kinase activity, with e lectrophoretic mobility retarded by serine/threonine phosphorylation) in M phase and the escape of mutation-activated p185(neu) from this r egulation. Our present results showed that retardation of electrophore tic mobility occurs independently of the cells' transformed status. We found that normal p185(neu) lost its ability to dimerize in the M pha se. We demonstrated a physical association between cdc2 (a serine/thre onine kinase, active in NI phase) and p185(neu). We showed that the ca rboxy terminal portion of p185(neu) is phosphorylated in vitro by cdc2 . Many phosphopeptides (at least three phosphoserine residues) unique to the M phase were identified, and the in vivo and irt vitro phosphop eptide patterns were superimposable. In contrast, mutation-activated p 185(neu) dimerized in the M phase with no changes in electrophoretic mobility, failed to associate with cdc2 and no unique phosphoserine re sidues could be identified in the M phase (data not shown), consistent with the escape of p185(neu) from cell cycle-dependent regulation. O ur results suggest that this escape is an intrinsic property of the mu tation-activated p185(neu) independent of its ability to transform ce lls. Our results also suggest the involvement of serine/threonine kina ses such as cdc2 in the cell cycle-dependent negative regulation of p1 85(neu).