Mapping the mechanisms that occur after an external cue is presented to a cell and the resultant signal transduction pathways that arise, has been a mainstay of cell biology for decades. As a result, more than 30% of all prescription drugs target pathways that are regulated by the major cell signaling molecule, G proteins. However, there has been some disagreement over the years concerning exactly how the signaling pathways are activated, since much evidence has been provided to show that the initiation is exclusively through G protein coupled receptors (GPCR).
Now, researchers at the University of California San Diego (UCSD) School of Medicine have published evidence demonstrating their ability to tune various cell types in vitro by manipulating G proteins through receptor tyrosine kinases (RTKs), a key signaling hub within almost all cell types.
“Our study shows the feasibility of targeting a hub in the cell signaling network to reset aberrant cell signaling from multiple pathways and receptors,” explained Pradipta Ghosh, M.D., associate professor of medicine at UCSD and senior author on the current study.
The findings from this study were published recently in PNAS through an article entitled “Multimodular biosensors reveal a novel platform for activation of G proteins by growth factor receptors.”
Specifically, Dr. Ghosh and her team created fluorescent biosensors that were derived from the signal transducing molecule Gα-interacting vesicle-associated protein (GIV), which binds RTKs and subsequently activates G proteins. The investigators used them in FRET and bimolecular complementation assays in order to visualize the signaling complex directly.
“Here we used molecular engineering to develop modular fluorescent biosensors that exploit the remarkable specificity of bimolecular recognition, i.e., of both G proteins and RTKs, and reveal the workings of a novel platform for activation of G proteins by RTKs in single living cells,” the scientists stated.
The two peptides that the USCD scientists generated effectively turned the G-protein pathway either on or off. In a series of cell culture experiments, the on peptides were observed to accelerate cells' ability to migrate after scratch-wounding assays. Conversely, the off peptide reduced the aggressiveness of cancer cells and decreased collagen production in cells associated with liver fibrosis. Additionally, when applied topically to mice, the on peptide was observed to accelerate skin wound healing.
“These studies not only provide evidence that GIV serves as a platform for transactivation of G proteins by growth factor RTKs but also illuminate the spatial and temporal dynamics of such noncanonical G protein signaling,” the researchers concluded.
Dr. Ghosh and her team are very excited about their preliminary findings and realize that the potential clinical value of the basic science discovery is the ability to eventually develop techniques that could slow or possibly even reverse the progression of diseases, such as cancer, which are driven by abnormal cell signaling along multiple pathways. “The takeaway is that we can begin to tap an emerging new paradigm of G protein signaling,” Dr. Ghosh said.