CRMP-2 regulates polarized Numb-mediated endocytosis for axon growth

Abstract

Axon growth during neural development is highly dependent on both cytoskeletal re-organization and polarized membrane trafficking. Previously, we demonstrated that collapsin response mediator protein-2 (CRMP-2) is critical for specifying axon/dendrite fate and axon growth in cultured hippocampal neurons, possibly by interacting with tubulin heterodimers and promoting microtubule assembly. Here, we identify Numb as a CRMP-2-interacting protein. Numb has been shown to interact with alpha-adaptin and to be involved in endocytosis. We found that Numb was associated with L1, a neuronal cell adhesion molecule that is endocytosed and recycled at the growth cone, where CRMP-2 and Numb were colocalized. Furthermore, expression of dominant-negative CRMP-2 mutants or knockdown of CRMP-2 message with small-interfering (si) RNA inhibited endocytosis of L1 at axonal growth cones and suppressed axon growth. These results suggest that in addition to regulating microtubule assembly, CRMP-2 is involved in polarized Numb-mediated endocytosis of proteins such as L1.

Hierarchical CRMP2 posttranslational modifications control NaV1.7 function

“…One possibility may be differential recruitment of the endocytic machinery or CRMP2 itself. Nedd4 proteins regulate trafficking of multiple sodium channels (6, 37) whereas Numb and Eps15 proteins are general players in clathrin-mediated endocytosis (18,19,27), so specificity is unlikely endowed by these proteins. Likely, the specificity is conferred by CRMP2, as its expression and modifications causally influence NaV1.7.…”

“…Having demonstrated that CRMP2 regulates endocytosis of NaV1.7, we next investigated the molecular mechanism involved. CRMP2 reportedly controls trafficking of membrane proteins and vesicles (8,15,18). As NaV1.7 endocytosis requires monoubiquitination by the ubiquitin ligase Nedd4-2 (24) and Numb-a CRMP2 protein partner acts as a scaffold between Nedd4 (25) and the endocytic machinery (19)-we hypothesized that recruitment of these proteins by CRMP2 may promote NaV1.7 internalization.…”

“…2 B-D), suggesting that CRMP2 can relocalize the channel away from the membrane to produce reduced current densities. Because CRMP2 interacts with the endocytic adaptor Numb (18) to regulate L1-cell adhesion molecule internalization via clathrin mediated endocytosis (19), we asked if loss of CRMP2 SUMOylation prevents NaV1.7 membrane localization by inducing its endocytosis. Pitstop2, a clathrin assembly inhibitor (23), prevented current density reductions imposed by loss of CRMP2 SUMOylation or Cdk5 phosphorylation (Fig.…”

Numb regulates vesicular docking for homotypic fusion of early endosomes via membrane recruitment of Mon1b

“…Numb localizes to endocytic organelles and participates in both clathrin-dependent and clathrin-independent endocytic trafficking of a number of key molecules such as Notch, EGFR, transferrin, integrin, N-cadherin, E-cadherin and L1 (a neuronal cell adhesion molecule) [9,[17][18][19][20][21]. Genetic evidence shows that Numb contributes to cell fate determination by antagonizing Notch activity in one of the two daughter cells after asymmetric cell division [2,3,22].…”

Unc-51-like kinase 1/2-mediated endocytic processes regulate filopodia extension and branching of sensory axons

“…axon growth ͉ dorsal root ganglion neurons ͉ endocytosis ͉ p62 E ndocytic processes play an active role during polarized axon elongation and growth cone navigation (1)(2)(3)(4)(5)(6)(7). However, the exact molecular mechanisms linking endocytosis to the signaling events downstream of growth factor-stimulated axon extensions are largely unknown.…”