Frizzled (Fz) receptors act as signal transducers of Wnt growth factors via several effector pathways, notably Wnt/2-catenin (2-cat) and Fz/planar cell polarity (PCP) signaling. Fz/PCP and Wnt-Fz/2-cat signaling diverge downstream of the cytoplasmic factor Dishevelled (Dsh). Often both pathways act in the same tissues, and a tight regulation of signaling specificity is essential for normal development and cellular homeostasis. In deregulated scenarios, selection of the wrong Fz-pathway often leads to disease (i.e. PKD or cancer). Although a molecular framework for both pathways is established, very little is known about the regulation of Wnt/Fz-Dsh signaling specificity. This application investigates the molecular aspects of signaling specificity distinguishing between Wnt-Fz/2-Cat and Fz/PCP signaling. We will address this in Drosophila (the model organism where both pathways were discovered) and in mammalian cell culture. The specific focus is the regulation of Dsh by phosphorylation. Dsh is a cytoplasmic factor shared between both pathways and recruited to the membrane by Fz receptors. Based on preliminary data we hypothesize that Dsh is differentially phosphorylated in a pathway specific manner. A combination of cell culture, in vivo, and biochemical studies will dissect the phosphorylation events on Dsh that switch its function between the Wnt- Fz pathways.
The Specific Aims are: 1. To determine specific phosphorylation event(s) on Dsh and their role in the selection of the signaling outcome;and 2. To identify and functionally define Tyrosine kinases acting in Dsh regulation and pathway specific responses. Our mass-spectrometry studies indicated that differential phosphorylation of Dsh contributes to pathway selection and we have identified several kinases acting on Dsh. Physiological and medical relevance of the phosphorylation events will be established in vivo. This will be complemented by the generation of specific antisera to the relevant phosphorylated sites in Dsh. These are likely to have diagnostic potential.
The regulation and selection of the correct Wnt signaling pathways is an essential feature of development and tissue function and homeostasis. Deregulation of Wnt is linked to many diseases, ranging from ciliopathies and angiogenesis defects, to cancer (e.g. several pathway components are tumor suppressors or proto-oncogenes). This application addresses the molecular regulation of Dishvelled a key component in Wnt/Frizzled-signaling specificity;the information acquired here will be of high significance for several medical disorders.
| Mlodzik, Marek (2016) The Dishevelled Protein Family: Still Rather a Mystery After Over 20 Years of Molecular Studies. Curr Top Dev Biol 117:75-91 |
