Casein kinase Iepsilon plays a functional role in the transforming growth factor-beta signaling pathway.
The transforming growth factor-beta (TGF-beta) signaling pathway is known to be involved in a wide range of biological events, including development, cellular differentiation, apoptosis, and oncogenesis. The TGF-beta signal is mediated by ligand binding to the type II receptor, leading to the recruitment and activation of the type I receptor, and subsequent activation of a family of intracellular signal transducing proteins called Smads. Here we report a regulatory role for casein kinase Iepsilon (CKIepsilon) in the TGF-beta signaling cascade. We find that CKIepsilon binds to all Smads and the cytoplasmic domains of the type I and type II receptors both in vitro and in vivo. The interaction of CKIepsilon with the type I and type II receptors is independent of TGF-beta stimulation, whereas the CKIepsilon/Smad interaction is transiently disrupted by ligand treatment. Additionally, CKIepsilon is able to phosphorylate the receptor-activated Smads (Smads 1-3 and 5) and the type II receptor in vitro. Transcriptional reporter assays reveal that transient overexpression of wild type CKIepsilon dramatically reduces basal reporter activity but enhances TGF-beta-stimulated transcription. Furthermore, overexpression of a kinase-dead mutant of CKIepsilon inhibits both basal and ligand-induced transcription, whereas inhibition of endogenous CKI catalytic activity with IC261 blocks only TGF-beta-stimulated reporter activity. Finally, knocking down CKIepsilon protein levels results in a significant increase in basal and TGF-beta-induced transcription. These results suggest that CKIepsilon plays a ligand-dependent, differential, and dual regulatory role within the TGF-beta signaling pathway.
Waddell
David S
DS
Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.
Liberati
Nicole T
NT
Guo
Xing
X
Frederick
Joshua P
JP
Wang
Xiao-Fan
XF
D000818:Animals; D047388:Casein Kinases; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D017930:Genes, Reporter; D006801:Humans; D008024:Ligands; D011485:Protein Binding; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D018125:Receptors, Transforming Growth Factor beta / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D051785:Smad Proteins; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000378:metabolism*
D004268:DNA-Binding Proteins; D008024:Ligands; D020033:Protein Isoforms; D034741:RNA, Small Interfering; D018125:Receptors, Transforming Growth Factor beta; D011993:Recombinant Fusion Proteins; D051785:Smad Proteins; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D011494:Protein Kinases; D047388:Casein Kinases