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Title: The Activity and Stability of p21 is Regulated by Non-Receptor Tyrosine Kinases

 

Speaker:Dr. Yongqi Huang
School of Chemistry and Chemical Engineering, Shandong University

 

Address: Rm 102, East wing of Old Chemistry Building, Peking Unversity

 

 

Chair: Prof. Zhirong Liu, Center for Quantitative Biology

 

 

 

 

Abtract:

    The Cip/Kip family of cyclin-dependent kinase (Cdk) inhibitors includes p21Cip1, p27Kip1 and p57Kip2. Their kinase inhibitory activities are mediated by a homologous N-terminal kinase-inhibitory domain (KID). The Cdk inhibitory activity and stability of p27 have been shown to be regulated by a two-step phosphorylation mechanism involving a tyrosine residue within the KID and a threonine residue within the flexible C-terminus. We show that these residues are conserved in p21 and p57, suggesting that a similar phosphorylation cascade regulates these Cdk inhibitors. However, the presence of a cyclin binding motif within its C-terminus alters the regulatory interplay between p21 and Cdk2/cyclin A, and its responses to tyrosine phosphorylation and altered p21:Cdk2/cyclin A stoichiometry. Although the Cip/Kip proteins can be phosphorylated in vitro by representatives of many non-receptor tyrosine kinase (NRTK) sub-families, the stability of p21 is not related to tyrosine phosphorylation in cell based experiments, suggesting that the stability and activity of Cip/Kip proteins are regulated via different mechanisms.