Doublecortin induces mitotic microtubule catastrophe and inhibits glioma cell invasion

Doublecortin (DCX) is a microtubule binding protein that induces growth arrest at the G2-M phase of cell-cycle in glioma and suppresses tumor xenograft in immunocompromised hosts. DCX expression was found in neuronal cells, but lacking in glioma cells. We tested the hypothesis that DCX inhibits glioma U87 cell mitosis and invasion. Our data showed that DCX synthesizing U87 cells underwent mitotic microtubule spindle catastrophe in a neurabin II dependent pathway. Synthesis of both DCX and neurabin II were required to induce apoptosis in U87 and HEK 293T cells. In DCX expressing U87 cells, association of phosphorylated DCX (P-DCX) with protein phosphatase-1 (PP1) in the cytosol disrupted the interaction between kinesin-13 and PP1 in the nucleus and yielded spontaneously active kinesin-13. The activated kinesin-13 caused mitotic microtubule catastrophe in spindle checkpoint. P-DCX induced depolymerization of actin filaments in U87 cells, downregulated matrix metalloproteinase -2 (MMP-2) and MMP-9, and inhibited glioma U87 cell invasion in a neurabin II dependent pathway. Thus, localization of the DCX-neurabin II-PP1 complex in the cytosol of U87 tumor cells inhibited PP1 phosphatase activities leading to anti-glioma effects via 1) mitotic microtubule spindle catastrophe that blocks mitosis, and 2) depolymerization of actin that inhibits glioma cell invasion.