SKA1 induces de novo MTX‐resistance in osteosarcoma through inhibiting FPGS transcription
2019
Yu, Wenxi | Min, Daliu | Lin, Feng | Zheng, Shuier | Tang, Lina | He, Aina | Hu, Haiyan | Shen, Zan
De novo methotrexate (MTX)‐resistance, whose underlying mechanism remains largely unknown, usually leads to very poor prognosis in patients with osteosarcoma (OS). In this study, we established the de novo MTX‐resistant OS cell line SF‐86 and identified the candidate gene spindle and kinetochore associated complex subunit 1 (SKA1) as potentially related to de novo MTX‐resistance. Analysis of a cohort of 95 OS patients demonstrated that SKA1 overexpression significantly correlated with de novo MTX‐resistance and poor 5‐year survival. Mechanistically, SKA1 overexpression lead to a downregulation of folylpoly‐γ‐glutamate synthetase (FPGS), a key enzyme that converts MTX into its active form, MTX‐PG. We further demonstrated that SKA1 interacts with DNA‐directed RNA polymerase II subunit RPB3. ChIP analysis revealed that RPB3 binds the promoter region of the FPGS gene and triggers FPGS transcription upon MTX treatment in SW1353, a MTX‐sensitive OS cell line lacking endogenous SKA1 expression. On the contrary, this process is blocked in SF‐86 cells due to the formation of an inhibitory SKA1‐RPB3 complex. Furthermore, downregulation of SKA1 levels restores MTX sensitivity in SF‐86. Collectively, our study has established the de novo MTX‐resistant cell line SF‐86 and identified SKA1 as a novel regulator of FPGS, playing a key role in the development of de novo MTX‐resistance in OS.
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