Receptor tyrosine kinases (RTKs) are a large family of cell surface receptors that sense growth factors and hormones and regulate a variety of cell behaviours in health and disease. Contactless activation of RTKs with spatial and temporal precision is currently not feasible. Here, we generated RTKs that are insensitive to endogenous ligands but can be selectively activated by low-intensity blue light. We screened light-oxygen-voltage (LOV)-sensing domains for their ability to activate RTKs by light-activated dimerization. Incorporation of LOV domains found in aureochrome photoreceptors of stramenopiles resulted in robust activation of the fibroblast growth factor receptor 1 (FGFR1), epidermal growth factor receptor (EGFR) and rearranged during transfection (RET). In human cancer and endothelial cells, light induced cellular signalling with spatial and temporal precision. Furthermore, light faithfully mimicked complex mitogenic and morphogenic cell behaviour induced by growth factors. RTKs under optical control (Opto-RTKs) provide a powerful optogenetic approach to actuate cellular signals and manipulate cell behaviour.

Optogenetics and photopharmacology provide spatiotemporally precise control over protein interactions and protein function in cells and animals. Optogenetic methods that are sensitive to green light and can be used to break protein complexes are not broadly available but would enable multichromatic experiments with previously inaccessible biological targets. Herein, we repurposed cobalamin (vitamin B12) binding domains of bacterial CarH transcription factors for green‐light‐induced receptor dissociation. In cultured cells, we observed oligomerization‐induced cell signaling for the fibroblast growth factor receptor 1 fused to cobalamin‐binding domains in the dark that was rapidly eliminated upon illumination. In zebrafish embryos expressing fusion receptors, green light endowed control over aberrant fibroblast growth factor signaling during development. Green‐light‐induced domain dissociation and light‐inactivated receptors will critically expand the optogenetic toolbox for control of biological processes.

Optogenetics and photopharmacology enable the spatiotemporal control of cell and animal behavior by light. Red light offers deep tissue penetration and minimal phototoxicity, but very few red light-sensitive optogenetic methods are currently available. Here, we developed a red light-induced homodimerization domain. We first showed that an optimized sensory domain of the cyanobacterial phytochrome 1 (CPH1) can be expressed robustly and without cytotoxicity in human cells. We then applied this domain to induce dimerization of two receptor tyrosine kinases, the fibroblast growth factor receptor 1 and the neurotrophin receptor trkB. With this new optogenetic method in hand, we activated the MAPK/ERK pathway non-invasively in mammalian tissue and developed multi-color cell signaling experiments. The light-controlled dimerizer and the red light-activated receptor tyrosine kinases will prove useful to regulate a variety of cellular processes with light.

High-throughput live-cell screens are intricate elements of systems biology studies and drug discovery pipelines. Here, we demonstrate an optogenetics-assisted method that obviates the addition of chemical activators and reporters, reduces the number of operational steps and increases information content in a cell-based small molecule screen against human protein kinases including an orphan receptor tyrosine kinase. This blueprint for all-optical screening can be adapted to many drug targets and cellular processes.Over the past decades, many chemical processes have been improved by replacing additives, such as catalysts, initiators or emulsifiers, with physical stimuli, such as light or ultrasound [1][2][3][4] . Although replacement results in reduced cost, increased robustness and improved sustainability, this general principle has not found many adaptations in chemical biology. Automated screens using living cells are essential in the identification and characterization of small molecules that act on disease-related proteins and cellular pathways. However, in many cell-based screens the need to add reagents that alter or report on cell activity results in complex operational design, high cost and sources of error. Furthermore, mammalian cells are sensitive to environmental perturbations (e.g. temperature or ionic strength) and subject to inherent variability. In neurobiology and cell biology, optogenetics and photopharmacology have recently harnessed the power of light to Reprints and permissions information is available online at http://www.nature.com/reprints/index.html.Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use

The insulin-like growth factor (IGF) axis is a molecular pathway intensively investigated in cancer research. Clinical trials targeting the IGF1 receptor (IGF1R) in different tumors, including prostate cancer, are under way. Although studies on the IGF axis in prostate cancer have already entered into clinical trials, the expression and functional role of the IGF axis in benign prostate and in prostate cancer needs to be better defined. We determined mRNA expression levels of the IGF axis in microdissected tissue specimens of local prostate cancer using quantitative PCR. All members of the IGF axis, including IGF1, IGF2, IGF binding proteins 1 through 6, and insulin receptor, were measured in both the stromal and epithelial compartments of the prostate. IGF1, IGF2, IGF1R, and insulin receptor were down-regulated in local prostate cancer tissue compared with matched benign tissue, suggesting that the IGF axis is not induced during prostate cancer development. Using a new prostate epithelial differentiation model, we demonstrate that the expression of the IGF axis is enhanced during normal prostate epithelial differentiation and regulated by tumor growth factor (TGF)-␤. Our data reveal a functional role of the IGF axis in prostate differentiation, underscoring the importance of the IGF axis in normal development and emphasizing the importance of accurate target validation before moving to advanced clinical trials.