Pavarotti/MKLP1 Regulates Microtubule Sliding and Neurite Outgrowth in Drosophila Neurons

SummaryRecently, we demonstrated that kinesin-1 can slide microtubules against each other, providing the mechanical force required for initial neurite extension in Drosophila neurons. This sliding is only observed in young neurons actively forming neurites and is dramatically downregulated in older neurons. The downregulation is not caused by the global shutdown of kinesin-1, as the ability of kinesin-1 to transport membrane organelles is not diminished in mature neurons, suggesting that microtubule sliding is regulated by a dedicated mechanism [1]. Here, we have identified the “mitotic” kinesin-6 Pavarotti (Pav-KLP) as an inhibitor of kinesin-1-driven microtubule sliding. Depletion of Pav-KLP in neurons strongly stimulated the sliding of long microtubules and neurite outgrowth, while its ectopic overexpression in the cytoplasm blocked both of these processes. Furthermore, postmitotic depletion of Pav-KLP in Drosophila neurons in vivo reduced embryonic and larval viability, with only a few animals surviving to the third instar larval stage. A detailed examination of motor neurons in the surviving larvae revealed the overextension of axons and mistargeting of neuromuscular junctions, resulting in uncoordinated locomotion. Taken together, our results identify a new role for Pav-KLP as a negative regulator of kinesin-1-driven neurite formation. These data suggest an important parallel between long microtubule-microtubule sliding in anaphase B and sliding of interphase microtubules during neurite formation

CLIP-170S is a microtubule +TIP variant that confers resistance to taxanes by impairing drug-target engagement

73 p.-5 fig.-1 tab.-11 fig supl.-2 vid. supl.Taxanes are widely used cancer chemotherapeutics. However, intrinsic resistance limits their efficacy without any actionable resistance mechanism. We have discovered a microtubule (MT) plus-end-binding CLIP-170 protein variant, hereafter CLIP-170S, which we found enriched in taxane-resistant cell lines and patient samples. CLIP-170S lacks the first Cap-Gly motif, forms longer comets, and impairs taxane access to its MT luminal binding site. CLIP-170S knockdown reversed taxane resistance in cells and xenografts, whereas its re-expression led to resistance, suggesting causation. Using a computational approach in conjunction with the connectivity map, we unexpectedly discovered that Imatinib was predicted to reverse CLIP-170S-mediated taxane resistance. Indeed, Imatinib treatment selectively depleted CLIP-170S, thus completely reversing taxane resistance. Other RTK inhibitors also depleted CLIP-170S, suggesting a class effect. Herein, we identify CLIP-170S as a clinically prevalent variant that confers taxane resistance, whereas the discovery of Imatinib as a CLIP-170S inhibitor provides novel therapeutic opportunities for future trials.This work was supported in part by the NIH T32 training grant 5T32CA062948 (to K.K.), the NIH T32 training grant 5T32CA062948 (to G.G.), the NIH T32 training grant 5T32CA203702 (to U.D.C.) by Clinical and Translational Science Center at Weill Cornell Medicine NIH/NCATS grant ULTR00457 (to G.G.), the NIH/NCI R01CA228512 (to P.G., M.A.S., and O.E.), NIH/NCI R21 CA216800 (to P.G.), NIH/NCI R01 CA179100 (to P.G.), DoD PC180637 (P.G., A.R.C.), and by the Ministerio de Economía y Competitividad grant BFU2016-75319-R and European Union H2020-MSCA-ITN-ETN/0582 ITN TUBINTRAIN (awarded to J.F.D.). D.S. was supported by the Intramural Research Program of the Eunice Kennedy Shriver National Institute of Child Health and Human Development, NIH. Y.L. and M.A.S. were supported, in part, by funds from the Clinical and Translational Science Center (CTSC), National Center for Advancing Translational Sciences (NCATS) of the National Institutes of Health, award # UL1-TR002384-01.Peer reviewe