ABSTRACT
3-Phosphoinositides are ubiquitous cellular lipids that play pivotal regulatory roles in health and disease. Among 3-phosphoinositides, phosphatidylinositol-3,5-bisphosphate (PI(3,5)P2) remains the least understood species in terms of its spatiotemporal dynamics and physiological function due to the lack of a specific sensor that allows spatiotemporally resolved quantitative imaging of PI(3,5)P2. Using a newly developed ratiometric PI(3,5)P2 sensor engineered from the C-terminal SH2 domain of Class I phosphoinositide 3-kinases (PI3K)-p85α subunit we demonstrate that a unique pool of PI(3,5)P2 is generated on lysosomes and late endosomes in response to growth factor stimulation. This PI(3,5)P2, the formation of which is mediated sequentially by Class II PI3KC2β and PIKfyve, plays a crucial role in terminating the activity of growth factor-stimulated Class I PI3K, one of the most frequently mutated proteins in cancer, via specific interaction with its regulatory p85 subunit. A small molecule inhibitor of p85α-PI(3,5)P2 binding specifically blocks the feedback inhibition of Class I PI3K by PI(3,5)P2 and thus serves as a PI3K activator that promotes neurite growth. Furthermore, cancer-causing mutations of the Class I PI3K-p85 subunit inhibit p85-PI(3,5)P2 interaction and thereby induce sustained activation of Class I PI3K. Our results unravel a hitherto unknown spatiotemporally specific regulatory function of PI(3,5)P2 that links Class I and II PI3Ks and modulates the magnitude of PI3K-mediated growth factor signaling. These results also suggest new therapeutic possibilities for treating cancer patients with p85 mutations and promoting wound healing and tissue regeneration.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
A small molecule inhibitor of p85α-PI(3,5)P2 binding that specifically blocks the feedback inhibition of Class I PI3K by PI(3,5)P2 and thus serves as a PI3K activator has been included.
