Abstract
FGFs and their high-affinity receptors (FGFRs) play key roles in development, tissue repair, and disease. Because FGFRs bind overlapping sets of ligands, their individual functions cannot be determined using ligand stimulation. Here, we generated a light-activated FGFR2 variant (OptoR2) to selectively activate signaling by the major FGFR in keratinocytes. Illumination of OptoR2-expressing HEK 293T cells activated FGFR signaling with remarkable temporal precision and promoted cell migration and proliferation. In murine and human keratinocytes, OptoR2 activation rapidly induced the classical FGFR signaling pathways and expression of FGF target genes. Surprisingly, multi-level counter-regulation occurred in keratinocytes in vitro and in transgenic mice in vivo, including OptoR2 down-regulation and loss of responsiveness to light activation. These results demonstrate unexpected cell type-specific limitations of optogenetic FGFRs in long-term in vitro and in vivo settings and highlight the complex consequences of transferring optogenetic cell signaling tools into their relevant cellular contexts.
Highlights
FGFs comprise a group of 22 structurally related proteins in mammals, which play key roles in development, repair, and disease (Beenken & Mohammadi, 2009; Ornitz & Itoh, 2015)
Because of the important function of FGFR2 in keratinocytes, we generated a version of this receptor, which gets activated by blue light instead of its natural ligand
human embryonic kidney (HEK) 293T cells, which stably and constitutively express OptoR2, responded to 15-min exposure to blue light with phosphorylation/ activation of ERK1/2, which was comparable to the level achieved with EGF (Fig 1B)
Summary
FGFs comprise a group of 22 structurally related proteins in mammals, which play key roles in development, repair, and disease (Beenken & Mohammadi, 2009; Ornitz & Itoh, 2015). Because of the important function of FGFR2 in keratinocytes, we generated a version of this receptor, which gets activated by blue light instead of its natural ligand (named OptoR2). Down-regulation of the receptor was observed in keratinocytes, suggesting that long-term activation of OptoR2, even at a low level, is deleterious for these cells.
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