Distinctive Effects of Phosphoinositides on Actin Reorganization

Phosphoinositide membrane lipids regulate diverse cellular functions including proliferation, differentiation, and migration. We have previously developed chemically-inducible dimerization techniques to manipulate phosphoinositides on a timescale of seconds and solved long-standing biological questions regarding their functions. This series of work has greatly impacted the fields of membrane lipids, ion channels and transporters, and the broader field of cell signaling. However, these findings also generated a new question of how this membrane lipid drives multiple cellular functions with high precision.  In order to address this, we developed two techniques based on rapamycin-induced protein dimerization to rapidly change plasma membrane PI(4,5)P2. First we increased PI(4,5)P2 by synthesis from PI(4)P using a membrane recruitable 5-kinase, and found that cells form actin comets (Movie #5). We then developed a second technique that increases the amount of available PI(4,5)P2 without consuming PI(4)P. This induced membrane ruffles (Movie #6). These distinct phenotypes were mediated by two signaling events: crosstalk between Rac and RhoA GTPases, and dynamin-mediated vesicular trafficking. Our results indicate that the effect of PI(4,5)P2 on actin reorganization depends on further phosphoinositides such as PI(4)P. Thus, combinatorial regulation may explain the diversity of phosphoinositide functions.
Schematic illustration of two techniques to rapidly manipulate PI(4,5)P2 by chemcially inducible dimerization. (Ueno et al. Sci Signaling, 2011)