In a new study published in Science Signaling, researchers at the University of Toronto’s Temerty Faculty of Medicine have shown that cell receptor clustering activates the Wnt signalling pathway, a step towards improving disease interventions.
According to Sarah Moldaver, a MSc graduate from the department of biochemistry and co-first author of the paper, disturbances in the pathway are linked to the development of degenerative diseases and cancers, making the understanding of Wnt receptor activation crucial for tailoring therapies.
“The behaviour of our cells drives these conditions, and one big component of that is the intracellular signalling pathways that tell cells how to act and behave,” says Moldaver.
Moldaver co-led the study alongside postdoctoral fellow Pierre Thibeault and was supervised by Stéphane Angers, director of the Donnelly Centre for Cellular & Biomolecular Research and a professor of biochemistry at Temerty Medicine.
Wnt signalling is an important mechanism by which cells transmit instructions to turn genes on or off in response to external cues, leading to proper development and maintenance of healthy tissues. The pathway starts when the Wnt protein attaches to a receptor protein called Frizzled on the cell’s surface. When a miscommunication occurs in the pathway, cells can receive the wrong cue to continue growing and dividing, leading to cancers.
“Wnt signalling has been studied for quite some time and yet there are many areas of Frizzled activation and signalling that are still not well understood,” says Thibeault.
Using synthetic antibodies characterized by the Angers lab, the researchers could turn on Frizzled receptors to specifically activate or deactivate parts of the pathways. In collaboration with Christopher Yip’s lab in the Faculty of Applied Science and Engineering, they deployed a super-resolution microscopy technique that allowed them to observe individual Frizzled receptor molecules on the surface of cells and provided direct evidence that clustering of multiple Frizzled proteins is a key step in the signalling pathway.
“While clustering of Frizzled receptors has been previously hypothesized to contribute to activation of the pathway, here we have provided direct biophysical evidence for it,” says Thibeault.
Their findings also show that Frizzled clustering and signalling can also work in an atypical way without the help of co-receptor proteins.
“Frizzled receptor clustering by itself without a co-receptor actually still does something downstream, but we don’t fully know what those pathways do” says Moldaver.
She says by understanding how Frizzled receives information from other cells, scientists can fine-tune pathways that are not functioning properly.
“If we’re going to modulate the pathway in any sort of way, whether to activate it or inactivate it in the context of different diseases, or even just to research it, we need to understand how the signal is first perceived by receptors to initiate the rest of the pathway,” says Moldaver.
She notes that many molecules are currently being developed as therapies to selectively inactivate or activate the Wnt pathway in various conditions.
“With improvements in rational drug design and the ability to activate Frizzled receptors with synthetic antibodies, we can begin to develop a better understanding of how to modulate diseases and aid in tissue regeneration,” says Thibeault.
There are 19 Wnt proteins in the human body, which are all capable of activating one or more of the 10 Frizzled receptors. Moldaver says the next step for this work will be figuring out the roles of each individual Frizzled receptor and their activation in specific cell types.
“Our paper shows that clustering of at least two receptors is important — but how many receptors actually form an active complex?” says Moldaver. “That would be really informative to better improve the selectivity of drugs.”
This research was funded by the Canadian Institutes of Health Research, U.S. National Institutes of Health and the Natural Sciences and Engineering Research Council of Canada.
