Cyclin E-Cdk2 Complex Regulate the Expression Level and Transcriptional Activity of STAT Proteins
Date Issued
2004
Date
2004
Author(s)
Huang, Chaio-Wei
DOI
zh-TW
Abstract
In mammals, the JAK-STAT pathways are known to play very important roles in cytokine signal transductaion. Members in this pathway include the Janus kinases (JAKs) family containing JAK1, JAK2, JAK3 and TYK2 and the STATs (signal transducer and activator of transcription), which contain STAT1 to STAT6. The activation of STATs provides a rapid method for transducing signal from membrane into nucleus, and this mechanism is conserved from insects to human.
However, the functional mechanism of this pathway is pooly understood in fish. We have constructed five STAT genes from pufferfish and also prepared STAT-JH1 chimeric proteins generated by fusion of the kinase domain (JH1 domain) of JAK1 kinase to the C-terminal end of STAT. To examine the function of STAT-JH1, we performed transfection study in COS-1 cells. Immunoblotting of cell lysate showed that the product of STAT-JH1 could undergo auto-tyrosine-phosphorylation. By immunocytochemistry, STAT-JH1 proteins are not only localized in cytoplasm but also could translocated into nucleus. In luciferase assay experiment, STAT-JH1 could enhance the transcriptional activity of β-casein promoter and inhibit the transcriptional activity of 14-3-3 ηpromoter. This finding indicates that STAT-JH1 proteins have transactivation ability without any extracellular stimulus.
Moreover, we studied the regulation of Cyclin E-Cdk2 on the protein expression and transcriptional activity of pufferfish STAT proteins. Different STATs were cotransfected with either Cyclin E or Cdk2 or Cyclin E and Cdk2 into COS-1 cells and the expression level of STAT proteins were analyzed. The results show that Cyclin E-Cdk2 could reduce STAT proteins expressions (STAT-HA or STAT-HA-JH1). In the presence of proteasome inhibitor，the low STAT proteins level will be rescued. By immunoprecipitation, STAT-HA-JH1 fusion protein can associate with Cdk2. We also found the transcriptional activity ofβ-casein promoter regulated by STAT-HA-JH1 was obviously inhibited by co-expression Cdk2 and Cyclin E. In summary, these data suggest that Cyclin E-Cdk2 is not merely one of the key regulators of the G1/S transition in the cell cycle. They maybe have connection with JAK/STAT pathway.
Subjects
轉錄因子
細胞週期蛋白
STAT
Cyclin E
Cdk2
Type
other
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