α2-Chimaerin, Cyclin-Dependent Kinase 5/p35, and Its Target Collapsin Response Mediator Protein-2 Are Essential Components in Semaphorin 3A-Induced Growth-Cone Collapse

Abstract

Neurite outgrowth is influenced by positive and negative signals that include the semaphorins, an important family of axonal outgrowth inhibitors. Here we report that the Rac GTPase activating protein (GAP) ␣2-chimaerin is involved in Semaphorin 3A (Sema 3A) signaling. In dorsal root ganglion neurons, Sema 3A-induced growth cone collapse was inhibited by ␣2-chimaerin mutated to eliminate GAP activity or interaction with phosphotyrosine. Activation of ␣2-chimaerin by phorbol ester caused growth cone collapse. Active ␣2-chimaerin interacts with collapsin response mediator protein-2 (CRMP-2) and cyclin-dependent kinase (Cdk) 5/p35 kinase through its SH2 and GAP domains, respectively. Cdk5 phosphorylates CRMP-2 at serine 522, possibly facilitating phosphorylation of serine 518 and threonine 514 by glycogen synthase kinase 3␤ (GSK3␤), a kinase previously implicated in Sema 3A signaling. Phosphorylation of CRMP-2 serine 522 was essential for Sema 3A-induced growth cone collapse, which is dependent on Cdk5 but not Rho kinase activity. ␣2-chimaerin, like CRMP-2, can associate with the Sema 3A receptor. These results indicate that active ␣2-chimaerin Rac GAP, Cdk5/p35, and its substrate CRMP-2, are implicated in the dynamics of growth cone guidance initiated through Sema 3A signaling.

Cdk5‐mediated phosphorylation of CRMP‐2 enhances its interaction with CaV2.2

“…Interestingly, Ca 2+ influx using mutations of the RhoK phosphorylation site (Thr-555) CRMP-2 was no different from wildtype CRMP-2, implying that RhoK does not regulate this interaction. In contrast, phosphorylation of CRMP-2 by either RhoK or Cdk5 leads to growth cone collapse [23,36] as well as disrupts interactions of CRMP-2 with both tubulin and numb [24]. Thus, phosphorylation of CRMP-2 by different kinases may allow fine tuning of only a subset of CRMP-2 interactions and functions and driving only particular signaling cascades.…”

Axon guidance in the developing ocular motor system and Duane retraction syndrome depends on Semaphorin signaling via alpha2-chimaerin

“…Several lines of evidence suggest that α2-chn mediates Semaphorin signaling in the OMN. In vivo phenotypes following knockdown of PlexinAs or α2-chn are closely similar, suggesting that α2-chn might be recruited to PlexinA/Neuropilin receptor complexes in OMN neurons, as is the case in dorsal root ganglion neurons where α2-chn is required for Sema3A-induced growth cone collapse (19). However, α2-chn's known association with tyrosine kinase receptors (20) may suggest the involvement of an additional signaling component(s).…”

Phosphorylation and mRNA Splicing of Collapsin Response Mediator Protein-2 Determine Inhibition of Rho-associated Protein Kinase (ROCK) II Function in Carcinoma Cell Migration and Invasion

“…Interaction-Some CRMP-2 activities are regulated through phosphorylation by Cdk5 or DYRK followed by GSK3 phosphorylation (33,34). A major pathway to regulate GSK3 activity is the PI3K-Akt pathway, which inhibits GSK3 activity through phosphorylation at Ser-9 of GSK3␤ (38).…”

“…Mimicking phosphorylation on Thr-514 correlates with reduced binding of CRMP-2 to tubulin (32). CRMP-2 is primed for GSK3 phosphorylation through phosphorylation by cyclin-dependent kinase 5 (Cdk5) or dual tyrosine-regulated kinase (DYRK) at Ser-22 (31)(32)(33)(34). In normal proliferating cells, GSK3␣/␤ are relatively inactive because of phosphorylation on serine 21/9 by Akt (35).…”