Functional Role of the Casein Kinase I (CKI) Family in the Transforming Growth Factor-Beta (TGF-Beta) Signaling Pathway
Abstract
The regulation of the Transforming Growth Factor-Beta (TGF-Beta signaling pathway and its role in cancer is an area of intense research. We are investigating the regulatory role of casein kinase I (CKI) in the TGF-Beta signaling cascade. We have found that all CKI isoforms (alpha, delta, epsilon, and gamma) can bind to Smads in vitro and that this interaction is mediated through the Mad Homology 2 (MH2) domain of the smad proteins. Furthermore, we have shown that CKI-epsilon can interact with smads and receptors in vivo, and that the CKI-epsilon/Type I and CKI-epsilon/Type II receptor interactions is independent of TGF-Beta ligand activity, while CKI-epsilon/Smad interaction is transiently disrupted by ligand stimulation. Since, CKI family members are serine/threonine kinase, we determined that CKI-epsilon and CKI-gamma-2 can both phosphorylate the receptor-activated Smads and the Type II Receptor, while CKI-gamma-2 can also phosphorylate the co-smad, Smad4 in vitro. Transcriptional reporter assays revealed that in the absence of TGF-Beta, transient overexpression of CKI-epsilon or CKI-gamma-2 dramatically reduced basal reporter activity, but in the presence of ligand CKI-epsilon enhanced and CKI-gamma-2 inhibited TGF-Beta mediated transcription. Furthermore, CKI-epsilon is also capable of significantly enhancing the transcriptional activity of smad3. Finally, we have shown that transient siRNA knock-down of all CKI isoforms resulted in dramatic increases in both basal and ligand stimulated transcriptional reporter activity. Taken together, these observations provide exciting evidence for a functional role for CKI in the TGF-Beta pathway, a pathway that has been shown to be involved in the development and progression of many different - types of cancers.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 2003
- Accession Number
- ADA421409
Entities
People
- David Waddell
- Nicole T. Liberati
- Xiao-Fan Wang
Organizations
- Duke University Hospital