Role of CLASP2 in microtubule stabilization and the regulation of persistent motility

In motile fibroblasts, stable microtubules (MTs) are oriented toward the leading edge of cells (1]. How these polarized MT arrays are established and maintained, and the cellular processes they control, have been the subject of many investigations. Several MT plus-end-tracking proteins, or + TIPs [2], have been proposed to regulate selective MT stabilization, including the CLASPs [3], a complex of CLIP-170, IQGAP1, activated Cdc42 or Rac1 [4], a complex of APC, EB1, and mDia1 [5], and the actin-MT crosslinking factor ACF7 [6]. By using mouse embryonic fibroblasts (MEFs) in a wound-healing assay, we show here that CLASP2 is required for the formation of a stable, polarized MT array but that CLIP-170 and an APC-EB1 interaction are not essential. Persistent motility is also hampered in CLASP2-deficient MEFs. We find that ACF7 regulates cortical CLASP localization in HeLa cells, indicating it acts upstream of CLASP2. Fluorescence-based approaches show that GFP-CLASP2 is immobilized in a bimodal manner in regions near cell edges. Our results suggest that the regional immobilization of CLASP2 allows MT stabilization and promotes directionally persistent motility in fibroblasts.