Optogenetic control of intracellular signaling pathways

Abstract

Cells employ a plethora of signaling pathways to make their life-and-death decisions. Extensive genetic, biochemical, and physiological studies have led to the accumulation of knowledge about signaling components and their interactions within signaling networks. These conventional approaches, although useful, lack the ability to control the spatial and temporal aspects of signaling processes. The recently emerged optogenetic tools open exciting opportunities by enabling signaling regulation with superior temporal and spatial resolution, easy delivery, rapid reversibility, fewer off-target side effects, and the ability to dissect complex signaling networks. Here we review recent achievements in using light to control intracellular signaling pathways and discuss future prospects for the field, including integration of new genetic approaches into optogenetics.

Keywords: Dronpa; LOV; UVR8; cryptochrome; intracellular signaling pathways; light-induced protein–protein interaction; oligomerization; optogenetics; photoactivatable proteins; phytochrome; signal transduction.

Figure 1

Scheme of light-induced conformational change in various photoactivatable proteins. The left bar illustrates the color of light (wavelength) that is used to stimulate photoactivation. Various protein pairs are shown on the right with light-induced inter-molecular change (UVR8, CRY2-CIB1, CRY2 alone, and PhyB-PIF) or intra-molecular change (LOV, Dronpa). For proteins containing cofactors (FMN, FAD, PCB), the yellow color marks the ground state and the white color marks the photo-activated state. UVR8 and Dronpa do not have cofactors and primarily use their tryptophan residues for photo reception.

Figure 2

Modes of signaling control by photoactivatable proteins. The target proteins (TP) can be activated by either photo-induced protein translocation (A-D) or uncaging (E-F). (A) Binding between TP1 (e.g. DNA binding domain) and TP2 (e.g. activation domain) can lead to activation of DNA transcription. TP1 and TP2 can also be split inteins which leads to protein splicing after protein binding. (B) Light can recruit signaling proteins to certain subcellular locations (e.g. the cytoplasmic leaflet of the plasma membrane) and activate downstream signaling pathways. (C) Light-induced oligomerization of CRY2 allows increase in the local concentration of signaling protein (e.g. receptor tyrosine kinase) and subsequent activation of downstream pathways. Oligomerization can also be used to conditionally inactivate protein activities. (D) The oligomeric states of UVR8 can be used to trap or release proteins from organelles (e.g. ER). (E-F) Photo-uncaging can release the steric inhibition of signaling components and activate downstream pathways.