Optogenetic control of phosphoinositide metabolism

Abstract

Phosphoinositides (PIs) are lipid components of cell membranes that regulate a wide variety of cellular functions. Here we exploited the blue light-induced dimerization between two plant proteins, cryptochrome 2 (CRY2) and the transcription factor CIBN, to control plasma membrane PI levels rapidly, locally, and reversibly. The inositol 5-phosphatase domain of OCRL (5-ptase OCRL ), which acts on PI(4,5)P 2 and PI(3,4,5)P 3 , was fused to the photolyase homology region domain of CRY2, and the CRY2-binding domain, CIBN, was fused to plasma membrane-targeting motifs. Blue-light illumination (458–488 nm) of mammalian cells expressing these constructs resulted in nearly instantaneous recruitment of 5-ptase OCRL to the plasma membrane, where it caused rapid (within seconds) and reversible (within minutes) dephosphorylation of its targets as revealed by diverse cellular assays: dissociation of PI(4,5)P 2 and PI(3,4,5)P 3 biosensors, disappearance of endocytic clathrin-coated pits, nearly complete inhibition of KCNQ2/3 channel currents, and loss of membrane ruffling. Focal illumination resulted in local and transient 5-ptase OCRL recruitment and PI(4,5)P 2 dephosphorylation, causing not only local collapse and retraction of the cell edge or process but also compensatory accumulation of the PI(4,5)P 2 biosensor and membrane ruffling at the opposite side of the cells. Using the same approach for the recruitment of PI3K, local PI(3,4,5)P 3 synthesis and membrane ruffling could be induced, with corresponding loss of ruffling distally to the illuminated region. This technique provides a powerful tool for dissecting with high spatial–temporal kinetics the cellular functions of various PIs and reversibly controlling the functions of downstream effectors of these signaling lipids.