MAPK-driven kinetochore stress in cancer

SUMMARY Kinetochores (KTs) are large protein structures assembled upon centromeres during mitosis that bind to microtubules (MTs) of the mitotic spindle to orchestrate and power chromosome movements. We have recently discovered that a high proportion of human glioblastoma isolates suffer from a lethal form of KT stress, which is triggered by oncogenic mitogen-activated protein kinase signaling [Mapk stressed KTs (MaSKs)]. MaSKs arise when the Ras-Raf-MEK-ERK cascade is inappropriately active in mitosis, resulting in hyperstimulation of a network of KT kinases that, in turn, hyperphosphorylate KTs, decreasing their MT binding capacity and causing excessive KT-MT turnover. The purpose of this grant is to reveal mechanistic details of our MaSK model while revealing MaSK relevance to KT and cancer biology. Our overarching hypothesis is that oncogenic RTK-Ras-Raf-MEK-ERK signaling alters the activity of key proteins involved in KT regulation causing cancer-specific destabilization of KT-MT attachments and requirement for MaSK-associated compensatory mechanisms. Aim 1 will investigate the nature, function, and regulation of MaSKs in glioblastoma isolates. Aim 2 will reveal the occurrence of MaSKs in patient tumors. Aim 3 will elucidate MaSK-induced vulnerabilities in cancer and transformed cells. MaSKs are highly relevant to cancer research. Our MaSK model provides a direct mechanism for chromosome instability induced by oncogenic Ras pathway signaling, which is a key knowledge gap. Moreover, we have only found MaSKs in cancer or transformed cells, where they trigger novel genetic and molecular dependencies not observed in normal cells. MaSK-containing cells differentially rely on two non-essential domains of the mitotic protein BubR1/BUB1B to facilitate recruitment of PP2A phosphatase to KTs to counteract MaSK-induced KT- MT instability. Further, MaSKs themselves can serve as biomarkers for tumors and can be leveraged to discover new MaSK-targeted therapies and to define a patient responder class.