Abstract
Wnt signaling pathways play important roles in various stages of developmental events and several aspects of adult homeostasis. Aberrant activation of Wnt signaling has also been associated with several types of cancer. We have recently identified Traf2- and Nck-interacting kinase (TNIK) as a novel activator of Wnt signaling through a comprehensive proteomic approach in human colorectal cancer cell lines. TNIK is an activating kinase for T-cell factor-4 (TCF4) and essential for the beta-catenin-TCF4 transactivation and colorectal cancer growth. Here, we report the essential role of TNIK in Wnt signaling during Xenopus development. We found that Xenopus TNIK (XTNIK) was expressed maternally and that the functional knockdown of XTNIK by catalytically inactive XTNIK (K54R) or antisense morpholino oligonucleotides resulted in significant malformations with a complete loss of head and axis structures. XTNIK enhanced beta-catenin-induced axis duplication and the expression of beta-catenin-TCF target genes, whereas knockdown of XTNIK inhibited it. XTNIK was recruited to the promoter region of beta-catenin-TCF target genes in a beta-catenin-dependent manner. These results demonstrate that XTNIK is an essential factor for the transcriptional activity of the beta-catenin-TCF complex and dorsal axis determination in Xenopus embryos.
Highlights
T-cell factor (TCF)2/lymphoid enhancer factor (LEF) family of nuclear proteins
Identification of Xenopus Traf2- and Nck-interacting kinase (TNIK)—A previously described registry has demonstrated the significant homology between human TNIK and Xenopus XTNIK in the UniGene Xenopus laevis database
We first examined the expression of XTNIK mRNA during Xenopus embryogenesis
Summary
T-cell factor (TCF)2/lymphoid enhancer factor (LEF) family of nuclear proteins. The -catenin and TCF/LEF complexes have been shown to contain a variety of protein components that modulate transcriptional activity [1,2,3,4,5]. Injection of XTNIK (K54R) mRNA into dorsal blastomeres of eight-cell stage embryos inhibited the initiation of gastrulation at stage 10 (supplemental Fig. S2) and resulted in significant axis defects with a complete loss of head and axis structures (Fig. 2A). Co-injection of XTNIK (WT) mRNA with a low dose of X-catenin (25 pg) into the ventral marginal zone of eight-cell stage embryos enhanced the formation of secondary axis with complete head structures.
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