title: Cyclin I-like (CCNI2) is a cyclin-dependent kinase 5 (CDK5) activator and is involved in cell cycle regulation.
abstract: In contrast to conventional cyclin-dependent kinases that are important for mitotic cell division, cyclin-dependent kinase 5 (CDK5) is predominantly activated in post-mitotic cells and is involved in various cellular events. The kinase activity of CDK5 is tightly regulated by specific activators including p35, p39, and cyclin I (CCNI). Here we show that cyclin I-like (CCNI2), a homolog of CCNI, interacts with CDK5 and activates the kinase activity of CDK5. Different from CCNI, which colocalizes with CDK5 in the nuclei in transfected cells, CCNI2 mainly retains CDK5 in the cytoplasm as well as on the cell membrane. Furthermore, although the expression level of CCNI2 mRNA and CCNI2 protein do not change significantly during cell cycle, depletion of CCNI2 with siRNA affects cell cycle progression as well as cell proliferation. In conclusion, our data strongly suggest that CCNI2 is a novel CDK5 activator and is involved in cell cycle regulation.
authors.affiliation: Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, Shandong University School of Life Sciences, Jinan, Shandong 250100, China.
authors.forename: Chengcheng
authors.initials: C
authors.lastname: Liu
authors.affiliation: Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, Shandong University School of Life Sciences, Jinan, Shandong 250100, China.
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Zhai
authors.affiliation: Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, Shandong University School of Life Sciences, Jinan, Shandong 250100, China.
authors.forename: Bin
authors.initials: B
authors.lastname: Zhao
authors.affiliation: Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, Shandong University School of Life Sciences, Jinan, Shandong 250100, China.
authors.forename: Yanfei
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Shandong Provincial Key Laboratory of Animal Cells and Developmental Biology, Shandong University School of Life Sciences, Jinan, Shandong 250100, China.
authors.forename: Zhigang
authors.initials: Z
authors.lastname: Xu
mesh_terms: D000072283:A549 Cells; D015153:Blotting, Western; D002453:Cell Cycle; D049109:Cell Proliferation; D056749:Cyclin I / Q000378:metabolism*; D051360:Cyclin-Dependent Kinase 5 / Q000378:metabolism*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006367:HeLa Cells; D006801:Humans; D025941:Protein Interaction Mapping; D020133:Reverse Transcriptase Polymerase Chain Reaction; D020798:Two-Hybrid System Techniques
chemical_list: C534756:CCNI protein, human; C000628769:CCNI2 protein, human; D056749:Cyclin I; D051360:Cyclin-Dependent Kinase 5