LncRNA KCNQ1OT1 enhanced the methotrexate resistance of colorectal cancer cells by regulating miR‐760/PPP1R1B via the cAMP signalling pathway

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Abstract
We aimed to explore the mechanism of the KCNQ1OT1/miR‐760/PPP1R1B axis acting to regulate methotrexate (MTX) resistance of colorectal cancer (CRC). Differentially expressed mRNAs and lncRNAs in MTX‐sensitive CRC cell lines and MTX‐resistant cell lines were determined through microarray analysis. Application of bioinformatics analysis was aimed to uncover the relationships among the lncRNAs/miRNAs/mRNAs, and to demonstrate the effects of cAMP signalling pathway in MTX‐resistant CRC. The expression level of RNA and proteins was, respectively, detected using qRT‐PCR and Western blot assays, whereas the dual‐luciferase reporter gene assay was implemented to verify the targeted relationship. The influence of the lncRNA/miRNA/mRNA axis on biological functions of MTX‐resistant cells and on the growth of tumours determined through both vitro and vivo experiments. LncRNA KCNQ1OT1 and PPP1R1B mRNA were overexpressed in MTX‐resistant CRC tumour cells. KCNQ1OT1 functioned as a sponge of miR‐760, which targeted PPP1R1B. Knockdown of KCNQ1OT1 enhanced chemosensitivity towards MTX through the sponging of miR‐760. MiR‐760 expressed at low levels targeted PPP1R1B in the activated cAMP signalling pathway under MTX treatment. Knockdown of KCNQ1OT1 dampened the proliferation of MTX‐resistant (HT29/MTX) cells by regulating the miR‐760/PPP1R1B axis, which also induced cell cycle arrest together with apoptosis. KCNQ1OT1 regulated the expression of PPP1R1B and the downstream genes CREB and CBP in the cAMP signalling pathway. MTX showed a suppressive function on CRC progression. KCNQ1OT1 enhanced the MTX resistance of CRC cells by regulating miR‐760‐mediated PPP1R1B expression via the cAMP signalling pathway.

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