Proteolysis of Xenopus Cip-type CDK inhibitor, p16Xic2, is regulated by PCNA binding and CDK2 phosphorylation

Cell Division

P Renee Yew⁴  Paul R Mueller⁶  Herbert B Rosenbaum³  Varija N Budhavarapu¹  Horng-Ru Lin⁵  Dong Hyun Kim⁴  Xi-Ning Zhu² 

[1] Current address: MD Anderson Cancer, Department of Biochemistry and Molecular Biology, University of Texas, Houston, TX, 77030, USA;Current address: DiaCarta Inc., P.O. Box 360772, Milpitas, CA, 95036, USA;Department of Molecular Medicine, Institute of Biotechnology, The University of Texas Health Science Center at San Antonio, San Antonio, TX 78229, USA;Department of Molecular Medicine, Institute of Biotechnology, Mail Code 8257, South Texas Research Facility, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA;Current address: Department of Infectious Diseases, Novartis Institute for Biomedical Research, 4560 Horton Street MS 4.3, Emeryville, CA, 94608-2916, USA;Department of Biology, The University of Texas at San Antonio, San Antonio, TX, 78249, USA

关键词: CDK inhibitor;    Proteolysis;    Phosphorylation;    PCNA;    Xenopus;    Xic2;   

Others  :  790797
DOI  :  10.1186/1747-1028-8-5

 received in 2013-01-25, accepted in 2013-04-17,  发布年份 2013

【 摘 要 】

Background

Cell division is positively regulated by cyclin-dependent kinases (CDKs) partnered with cyclins and negatively regulated by CDK inhibitors. In the frog, Xenopus laevis, three types of CDK inhibitors have been described: p27^Xic1 (Xic1) which shares sequence homology with both p21^Cip1 and p27^Kip1 from mammals, p16^Xic2 (Xic2) which shares sequence homology with p21^Cip1, and p17^Xic3 (Xic3) which shares sequence homology with p27^Kip1. While past studies have demonstrated that during DNA polymerase switching, Xic1 is targeted for protein turnover dependent upon DNA, Proliferating Cell Nuclear Antigen (PCNA), and the ubiquitin ligase CRL4^Cdt2, little is known about the processes that regulate Xic2 or Xic3.

Methods

We used the Xenopus interphase egg extract as a model system to examine the regulation of Xic2 by proteolysis and phosphorylation.

Results

Our studies indicated that following primer synthesis during the initiation of DNA replication, Xic2 is targeted for DNA- and PCNA-dependent ubiquitin-mediated proteolysis and that Cdt2 can promote Xic2 turnover. Additionally, during interphase, Xic2 is phosphorylated by CDK2 at Ser-98 and Ser-131 in a DNA-independent manner, inhibiting Xic2 turnover. In the presence of double-stranded DNA ends, Xic2 is also phosphorylated at Ser-78 and Ser-81 by a caffeine-sensitive kinase, but this phosphorylation does not alter Xic2 turnover. Conversely, in the presence or absence of DNA, Xic3 was stable in the Xenopus interphase egg extract and did not exhibit a shift indicative of phosphorylation.

Conclusions

During interphase, Xic2 is targeted for DNA- and PCNA-dependent proteolysis that is negatively regulated by CDK2 phosphorylation. During a response to DNA damage, Xic2 may be alternatively regulated by phosphorylation by a caffeine-sensitive kinase. Our studies suggest that the three types of Xenopus CDK inhibitors, Xic1, Xic2, and Xic3 appear to be uniquely regulated which may reflect their specialized roles during cell division or early development in the frog.

【 授权许可】

   
2013 Zhu et al.; licensee BioMed Central Ltd.

【 图 表 】

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