Membrane-Permeant Phosphoinositide Derivatives as Modulators of Growth Factor Signaling and Neurite Outgrowth

Phosphoinositides are important signaling molecules that govern a large number of cellular processes such as proliferation, differentiation, membrane remodeling, and survival. Here we introduce a fully synthetic membrane-permeant derivative of a novel, easily accessible, and very potent phosphatidylinositol 3,4,5-trisphosphate [Ptdlns(3,4,5)P-3] mimic: phosphatidylinositol 3,4,5,6-tetrakisphosphate [Ptdlns(3,4,5,6)P-4]. The membrane-permeant PtdIns(3,4,5,6)P-4 derivative activated pathways downstream of phosphatidylinositol 3-kinase (PI3K), including protein kinase 13, p70S6K, mitogen-activated protein kinase, and protein kinase C, more potently than similar membrane-permeant PtdIns(3,4,5)P-3 and PtdIns(3,4)P-2 derivatives in the absence of receptor stimulation. In addition, we demonstrate that treatment of PC12 cells with the membrane-permeant PtdIns(3,4)P-2, PtdIns(3,4,5)P-3, and Ptdlns(3,4,5,6)P-4 derivatives increases the number of neurites per cell in the presence of NGF. This work establishes membrane-permeant phosphoinositides as powerful tools to study PI3K signaling and directly demonstrates that 3-phosphorylated phosphoinositides are instrumental for neurite initiation.