Collapsin Response Mediator Proteins (CRMPs) Are a New Class of Microtubule-associated Protein (MAP) That Selectively Interacts with Assembled Microtubules via a Taxol-sensitive Binding Interaction

Abstract

Background: CRMPs play roles in axon specification and semaphorin 3A-induced growth cone collapse, but their biochemical function is unclear. Results: CRMPs are found to bind directly to microtubules through a conserved C-terminal region. Conclusion: CRMPs can stabilize microtubules but are negatively regulated by phosphorylation. Significance: This work can explain phenotypes associated with loss of CRMPs on axon specification and dendritic arborization. Collapsin response mediator proteins are ubiquitously expressed from multiple genes (CRMPs 1-5) and play important roles in dividing cells and during semaphorin 3A (Sema3A) signaling. Nonetheless, their mode of action remains opaque. Here we carried out in vivo and in vitro assays that demonstrate that CRMPs are a new class of microtubule-associated protein (MAP). In experiments with CRMP1 or CRMP2 and their derivatives, only the C-terminal region (residues 490 -572) mediated microtubule binding. The in vivo microtubule association of CRMPs was abolished by taxol or epothilone B, which is highly unusual. CRMP2-depleted cells exhibited destabilized anaphase astral microtubules and altered spindle position. In a cell-based assay, all CRMPs stabilized interphase microtubules against nocodazole-mediated depolymerization, with CRMP1 being the most potent. Remarkably, a 82-residue C-terminal region of CRMP1 or CRMP2, unrelated to other microtubule binding motifs, is sufficient to stabilize microtubules. In cells, we demonstrate that glycogen synthase kinase-3 (GSK3) inhibition potentiates this activity. Thus, CRMPs are a new class of MAP that binds through a unique motif, but in common with others such as Tau, is antagonized by GSK3. This regulation is consistent with such kinases being critical for the Sema3A (collapsin) pathway. These findings have implications for cancer and neurodegeneration.