Role of co-receptors LRP6 and Tspan12 in Norrin/ß-catenin signaling
Abstract/Contents
- Abstract
- The Wnt/β-catenin signaling pathway co-evolved with multicellularity and dictates embryogenesis and tissue renewal across metazoans. In this pathway, the secreted growth factor Wnt binds and heterodimerizes the receptors Frizzled (Fzd1-10) and Low-density lipoprotein receptor-related protein 5 or 6 (LRP5/6) in the plasma membrane; this ultimately leads to the stabilization of transcriptional co-activator β-catenin, which directs the transcription of target genes. This pathway is also activated by the atypical ligand Norrin. In response to Wnt or Norrin binding to Fzd and LRP5/6, Dishevelled (Dvl1-3) is recruited from the cytoplasm to the plasma membrane. Dvl is essential to Wnt/β-catenin signal transduction because it bridges the receptors with downstream signaling partners, yet how Dvl is recruited to the membrane in response to ligand binding is unclear. Wnt ligands generate Fzd-LRP5/6 heterodimers and may also homodimerize Fzd, but it is not known whether or how these receptor complexes work together to transduce the ligand-binding signal to Dvl. Further, although Fzd and LRP5/6 are sufficient for Wnt-stimulated signaling, and Norrin simultaneously binds these two receptors, Norrin-stimulated signaling additionally requires the membrane protein Tetraspanin-12 (Tspan12) through an unknown mechanism. Tspan12 coimmunoprecipitates with Fzd4 and Norrin, suggesting that it acts as a co-receptor. In this dissertation, I develop biochemical tools to investigate whether the Fzd-Dvl interaction is directly strengthened either by ligand binding to Fzd or by Fzd homo- or heterodimerization with LRP5/6 or Tspan12. Using purified protein, I find that Fzd-Dvl affinity is agnostic to ligand binding or Fzd homo- or heterodimerization. Instead, we show that Fzd-Dvl binding is highly dependent on the lipid phosphatidylinositol 4,5-bisphosphate. I also find that Tspan12 directly binds Norrin with nanomolar affinity, and provide data consistent with a model in which Tspan12 captures Norrin on the cell surface, then hands it off to Fzd4 for association with LRP5/6 and subsequent signaling. This work builds on our understanding of the direct physical interactions that underlie signal initiation in Wnt- and Norrin/β-catenin signaling.
Description
| Type of resource | text |
|---|---|
| Form | electronic resource; remote; computer; online resource |
| Extent | 1 online resource. |
| Place | California |
| Place | [Stanford, California] |
| Publisher | [Stanford University] |
| Copyright date | 2023; ©2023 |
| Publication date | 2023; 2023 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Author | Bruguera, Elise |
|---|---|
| Degree supervisor | Kobilka, Brian K |
| Thesis advisor | Kobilka, Brian K |
| Thesis advisor | Feng, Liang, 1976- |
| Thesis advisor | Huttenhain, Ruth |
| Thesis advisor | Nusse, Roel, 1950- |
| Degree committee member | Feng, Liang, 1976- |
| Degree committee member | Huttenhain, Ruth |
| Degree committee member | Nusse, Roel, 1950- |
| Associated with | Stanford University, School of Medicine |
| Associated with | Stanford University, Department of Molecular and Cellular Physiology |
Subjects
| Genre | Theses |
|---|---|
| Genre | Text |
Bibliographic information
| Statement of responsibility | Elise Sumiko Bruguera. |
|---|---|
| Note | Submitted to the Department of Molecular and Cellular Physiology. |
| Thesis | Thesis Ph.D. Stanford University 2023. |
| Location | https://purl.stanford.edu/hc691zr3480 |
Access conditions
- Copyright
- © 2023 by Elise Bruguera
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
Also listed in
Loading usage metrics...