Figure 7.

Model for the mechanism of Xe-Cdc25A degradation and cell cycle arrest induced by the ERK pathway. On strong activation of the ERK pathway, ERK phosphorylates Xe-Cdc25A on S85 (which normally is phosphorylated by Cdk) and other Ser residues (omitted), whereas the downstream kinase p90rsk phosphorylates Xe-Cdc25A on other multiple Ser residues (which overlap with Chk1 phosphorylation sites). These phosphorylations facilitate ubiquitination of Xe-Cdc25A by SCF^β-TrCP, thereby targeting the phosphatase for degradation and causing cell cycle arrest at interphase. For details, see text. RD, regulatory domain; DDG, DDG motif; CD, catalytic domain.