Regulation of the Wnt Pathway by TGFbeta and DYRK2: Mechanisms of Disease and Signal Transduction
Baskir, Rubin Sam
My thesis is composed of two independent projects related by the Wnt signaling transduction pathway. The first project provides evidence that vascular-associated adult lung mesenchymal stem cells (MSCs) respond to bleomycin injury by increasing the transcription of Wnt target genes during the inflammatory phase and that this increase in transcription is associated with MSC-to-myofibroblast (MyoFB) differentiation. Using FACs and histological analyses in mice I showed that Wnt activation in lung MSC increases during the inflammatory phase after bleomycin injury. I demonstrated that TGF induced expression of MyoFB and Wnt target genes in cultured MSCs by quantitative qPCR and that TGF1 induced activation of a TOPFLASH reporter. Finally, I showed that pyrvinium, a small molecule that potentiates the activity of CK1 and increases -catenin degradation, decreases TGF1 induction of endogenous Wnt and MyoFB target genes. The second project provides evidence that the novel kinase DYRK2 enhances Wnt signaling pathway activation by promoting LRP6 phosphorylation (an indication of pathway activation) via regulation of GSK3 enzymatic activity. Evidence that DYRK2 regulates the Wnt pathway comes from my demonstration that DYRK2 1) induces Xenopus axis duplication, 2) promotes Wnt reporter activity, 3) increases intracellular -catenin levels, and 4) promotes LRP6 phosphorylation. My morpholino studies in Xenopus embryos and small molecule inhibitor studies in cultured cells suggest a requirement for DYRK activity in vivo and in cultured cells. Finally, I provide mechanistic evidence that DYRK2 promotes Wnt signaling by binding to GSK3 and enhancing its activity towards LRP6.