GAP43, MARCKS, and CAP23 modulate PI(4,5)P-2 at plasmalemmal rafts, and regulate cell cortex actin dynamics through a common mechanism

The dynamic properties of the cell cortex and its actin cytoskeleton determ ine important aspects of cell behavior and are a major target of cell regul ation. GAP43, myristoylated alanine-rich C kinase substrate (MARCKS), and C AP23 (GMC) are locally abundant, plasmalemma-associated PKC substrates that affect ac tin cytoskeleton. Their expression correlates with morphogenic p rocesses and cell motility, but their role in cortex regulation has been di fficult to define mechanistically. We now show that the three proteins accu mulate at rafts, where they codistribute with PI(4,5)P-2, and promote its r etention and clustering. Binding and modulation of PI(4,5)P-2 depended on t he basic effector domain (ED) of these proteins, and constructs lacking the ED functioned as dominant inhibitors of plasmalemmal PI(4,5)P-2 modulation . In the neuronlike cell line, PC12, NGF- and substrate-induced peripheral actin structures, and neurite outgrowth were greatly augmented by any of th e three proteins, and suppressed by Delta ED mutants. Agents that globally mask PI(4,5)P-2 mimicked the effects of GMC on peripheral actin recruitment and cell spreading, but interfered with polarization and process formation . Dominant negative GAP43(Delta ED) also interfered with peripheral nerve r egeneration, stimulus-induced nerve sprouting and control of anatomical pla sticity at the neuromuscular junction of transgenic mice. These results sug gest that GMC are functionally and mechanistically related PI(4,5)P-2 modul ating proteins, upstream of actin and cell cortex dynamics regulation.