Regulation Of Breast Tumor Angiogenesis And Paclitaxel Sensitivity By CLIP-170

CLIP-170is one of the classic microtubule binding proteins that interacts with microtubules through its N-terminal CAP-Gly domains. Compelling evidence has shown that CLIP-170co-localizes with microtubule distal ends and regulates microtubule dynamics. CLIP-170has been demonstrated to participate in diverse microtubule associated cellular activities, such as the formation of kinetochore-microtubule attachment during mitosis and directional cell migration, primarily through its regulation of microtubule dynamics. In addition, CLIP-170has been shown to regulate lamellipodia formation and cell invasion in invasive human breast cancer cells by modulating the association of IQGAP1and kinesin with the Racl CLIP-170complex.Tumor associated angiogenesis involves a complex interplay of a variety of cell types in the tumor microenvironment. This striking feature raises therapeutic opportunities for targeting multiple aspects of angiogenesis to inhibit tumor progression. Although current antiangiogenic strategies have shown promising results in several cancer types, identification of additional antiangiogenic targets is required to improve the therapeutic response. Herein, we show that the microtubule binding protein CLIP-170is highly expressed in breast tumor samples and correlates positively with blood vessel density. Depletion of CLIP-170significantly impaired vascular endothelial tube formation and sprouting in vitro and inhibited breast tumor growth in mice by decreasing tumor vascularization. Our data further show that CLIP-170is important for the migration but not the proliferation of vascular endothelial cells. In addition, CLIP-170promotes the polarization of endothelial cells in response to the angiogenic stimulus. These findings thus demonstrate a critical role for CLIP-170in tumor angiogenesis and suggest its potential as a novel antiangiogenic target.In our study, we report for the first time that CLIP-170regulates the sensitivity of breast cancer cells to paclitaxel via a microtubule dependent mechanism. The study thus identifies a previously unrecognized role for CLIP-170in regulating paclitaxel sensitivity. By in vitro cell proliferation assay, we demonstrated that the CLIP-170expression level correlates with paclitaxel sensitivity in breast cancer cell lines. Importantly, we have also shown that the expression of CLIP-170in breast cancer samples correlates with the pathological response of tumours to paclitaxel containing chemotherapy. Mitotic index and caspase-3activity analyses reveal that CLIP-170increases the abilities of paclitaxel to block cell cycle progression at mitosis and to induce apoptosis in breast cancer cells. By.microtubule sedimentation assay and binding affinity analysis, we further find that CLIP-170promotes paclitaxel binding to microtubules. In vitro tubulin polymerization assay shows that CLIP-170enhances the activity of paclitaxel to promote microtubule assembly. These results demonstrate that CLIP-170mediates paclitaxel sensitivity in breast cancer via a microtubule-dependent mechanism.It has been shown previously that certain microtubule binding proteins could affect the ability of microtubule targeting drugs to interact with microtubules through structural or allosteric effects, thereby influencing drug sensitivity to control the tumor development. Given that CLIP-170is highly expressed and correlates positively with vascular density in breast cancer and that targeting endothelial cells offers therapeutic benefit, inhibiting CLIP-170alone or in combination with other therapeutics might be useful for the management of breast cancer.