| 1. |
- Arthofer, Elisa
(author)
-
A frizzled quest to dissect the molecular pharmacology of WNT signaling : from biology to signaling mechanism(s)
- 2017
-
Doctoral thesis (other academic/artistic)abstract
- The wingless/int1 (WNT)/Frizzled (FZD) family of signal transduction pathways is highly conserved across species and controls essential physiological functions important for embryonic development, stem cell renewal, proliferation, differentiation, and cell polarity. Dysregulation of these signaling pathways leads to developmental abnormalities or other conditions such as inflammation, cancer, or neurological disorders. In mammals, 19 different WNTs can bind to and interact with ten isoforms of FZD in a plethora of combinations. These seven transmembrane-spanning receptors are categorized in the Class Frizzled within the superfamily of G protein-coupled receptors (GPCRs). Several important co-factors are known to aid in the activation of WNT/FZD signaling, such as Disheveled (DVL) or low density lipoprotein receptor related protein 5 and 6 (LRP5/6). In addition, interactions of FZDs with heterotrimeric G proteins have continuously been reported. Upon ligand binding, activation of β-catenin-dependent and/or β-catenin-independent downstream signaling pathways takes place. The overall aim of this thesis was to shed light on mechanistics of WNT/FZD signaling and pharmacology from different angles: In paper I, we investigated the presence and role of WNT-5A in human glioblastomas, a WNT important for neurological functions in the central nervous system (CNS) and found to be dysregulated in many cancers. In this study, we describe the correlative nature of high WNT-5A expression with upregulation of genes involved in immunological processes as well as increased microglia infiltration in the tumor microenvironment. In paper II and III, we focus on FZD4, a FZD isoform important for retinal vascularization. We provide functional evidence for the interaction of FZD4 with heterotrimeric Gα12/13, which is independent of DVL and LRP5/6, and show activation of downstream signaling events. We further describe a novel signaling route through NorrinFZD4-Gα12/13, which exerts an inhibitory effect on the classical Norrin-FZD4-β-catenin signaling pathway known to be important in angiogenesis, thus arguing for a concept of cross-talk and feedback inhibition from the same FZD isoform, a notion that is as of yet completely unappreciated. In addition, this thesis tries to point out the current limitations and struggles in the field of studying WNT/FZD signaling and the need for further studies identifying crucial links to signal specification, which would aid in future drug development targeting this pathway.
|
|
| 2. |
- Dijksterhuis, Jacomijn P., et al.
(author)
-
High levels of WNT-5A in human glioma correlate with increased presence of tumor-associated microglia/monocytes
- 2015
-
In: Experimental Cell Research. - : Elsevier. - 0014-4827 .- 1090-2422. ; 339:2, s. 280-288
-
Journal article (peer-reviewed)abstract
- Malignant gliomas are among the most severe types of cancer, and the most common primary brain tumors. Treatment options are limited and the prognosis is poor. WNT-5A, a member of the WNT family of lipoglycoproteins, plays a role in oncogenesis and tumor progression in various cancers, whereas the role of WNT-5A in glioma remains obscure. Based on the role of WNT-5A as an oncogene, its potential to regulate microglia cells and the glioma-promoting capacities of microglia cells, we hypothesize that WNT-5A has a role in regulation of immune functions in glioma. We investigated WNT-5A expression by in silico analysis of the cancer genome atlas (TCGA) transcript profiling of human glioblastoma samples and immunohistochemistry experiments of human glioma tissue microarrays (TMA). Our results reveal higher WNT-5A protein levels and mRNA expression in a subgroup of gliomas (WNT-5A(high)) compared to non-malignant control brain tissue. Furthermore, we show a significant correlation between WNT-5A in the tumor and presence of major histocompatibility complex Class II-positive microglia/monocytes. Our data pinpoint a positive correlation between WNT-5A and a proinflammatory signature in glioma. We identify increased presence of microglia/monocytes as an important aspect in the inflammatory transformation suggesting a novel role for WNT-5A in human glioma.
|
|
| 3. |
- Strakova, Katerina, et al.
(author)
-
The tyrosine Y250(2.39) in Frizzled 4 defines a conserved motif important for structural integrity of the receptor and recruitment of Disheveled
- 2017
-
In: Cellular Signalling. - : Elsevier BV. - 0898-6568 .- 1873-3913. ; 38, s. 85-96
-
Journal article (peer-reviewed)abstract
- Frizzleds (FZDs) are unconventional G protein-coupled receptors, which activate diverse intracellular signaling pathways via the phosphoprotein Disheveled (DVL) and heterotrimeric G proteins. The Interaction interplay of FZDs with DVL and G proteins is complex, involves different regions of FZD and the potential dynamics are poorly understood. In the present study, we aimed to characterize the function of a highly conserved tyrosine (Y250(2.39)) in the intracellular loop 1 (ILl) of human FZD(4). We have found Y250(2.39) to be crucial for DVL2 interaction and DVL2 translocation to the plasma membrane. Mutant FZD4-Y250(2.39)F, impaired in DVL2 binding, was defective in both beta-catenin-dependent and beta-catenin-independent WNT signaling induced in Xenopus laevis embryos. The same mutant maintained interaction with the heterotrimeric G proteins Gan and G alpha(13) and was able to mediate WNT-induced G protein dissociation and G protein-dependent YAP/TAZ signaling. We conclude from modeling and dynamics simulation efforts that Y250(2.39) is important for the structural integrity of the FZD-DVL, but not for the FZD-G protein interface and hypothesize that the interaction network of Y250(2.39) and H348(4.46) plays a role in specifying downstream signaling pathways induced by the receptor.
|
|
