The MuvB multiprotein complex, together with B-MYB and FOXM1 (MMB-FOXM1), plays an essential role in cell cycle progression by regulating the transcription of genes required for mitosis and cytokinesis. In many tumors, B-MYB and FOXM1 are overexpressed as part of the proliferation signature. However, the transcriptional targets that are important for oncogenesis have not been identified. Given that mitotic kinesins are highly expressed in cancer cells and that selected kinesins have been reported as target genes of MMB-FOXM1, we sought to determine which mitotic kinesins are directly regulated by MMB-FOXM1. We demonstrate that six mitotic kinesins and two microtubule-associated non-motor proteins (MAPs) CEP55 and PRC1 are direct transcriptional targets of MuvB, B-MYB and FOXM1 in breast cancer cells. Suppression of KIF23 and PRC1 strongly suppressed proliferation of MDA-MB-231 cells. The set of MMB-FOXM1 regulated kinesins genes and 4 additional kinesins which we referred to as the mitotic kinesin signature (MKS) is linked to poor outcome in breast cancer patients. Thus, mitotic kinesins could be used as prognostic biomarker and could be potential therapeutic targets for the treatment of breast cancer.
In this study, we investigated whether proteins that are involved in cytokinesis are potential targets for therapy of lung cancer. We find that the microtubule-associated protein PRC1 (protein required for cytokinesis 1), which plays a key role in organizing anti-parallel microtubule in the central spindle in cytokinesis, is overexpressed in lung cancer cell lines compared to normal cells. Increased expression of PRC1 is correlated with a poor prognosis of human lung adenocarcinoma patients. Lentiviral delivered, inducible RNAi of PRC1 demonstrated that proliferation of lung cancer cell lines strongly depends on PRC1. Significantly, we also show that PRC1 is required for tumorigenesis in vivo using a mouse model for non-small cell lung cancer driven by oncogenic K-RAS and loss of p53. When PRC1 is depleted by in vivo RNA interference, lung tumor formation is significantly reduced. Although PRC1 has been suggested to regulate Wnt/ß-catenin signaling in cancer cells, we find no evidence for a role of PRC1 in this pathway in lung cancer. Instead, we show that the depletion of PRC1 results in a strong increase in bi- and multinuclear cells due to defects in cytokinesis. This ultimately leads to apoptosis and senescence. Together these data establish PRC1 as a potential target for therapy of lung cancer.
Trypanosomes are masters of adaptation to different host environments during their complex life cycle. Large-scale proteomic approaches provide information on changes at the cellular level, and in a systematic way. However, detailed work on single components is necessary to understand the adaptation mechanisms on a molecular level. Here, we have performed a detailed characterization of a bloodstream form (BSF) stage-specific putative flagellar host adaptation factor Tb927.11.2400, identified previously in a SILAC-based comparative proteome study. Tb927.11.2400 shares 38% amino acid identity with TbFlabarin (Tb927.11.2410), a procyclic form (PCF) stage-specific flagellar BAR domain protein. We named Tb927.11.2400 TbFlabarin-like (TbFlabarinL), and demonstrate that it originates from a gene duplication event, which occurred in the African trypanosomes. TbFlabarinL is not essential for the growth of the parasites under cell culture conditions and it is dispensable for developmental differentiation from BSF to the PCF in vitro. We generated TbFlabarinL-specific antibodies, and showed that it localizes in the flagellum. Co-immunoprecipitation experiments together with a biochemical cell fractionation suggest a dual association of TbFlabarinL with the flagellar membrane and the components of the paraflagellar rod.
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