MiR-505 mediates methotrexate resistance in colorectal cancer by targeting RASSF8.

OBJECTIVE: To investigate the relationship between miR-505 and RASSF8 as well as the effect of miR-505 on methotrexate (MTX) resistance of human colorectal cancer (CRC).

METHODS: Microarray was used to select differentially expressed miRNAs. QRT-PCR and western blot were performed to assess miR-505 and RASSF8 mRNA levels in MTX-sensitive and MTX-resistant CRC tissues and cells. Cell viability, propagation and apoptosis were confirmed by MTT, colony formation assays and flow cytometry. Transwell and wound healing assays were conducted on cancerous cells to determine cell metastasis. The target relationship between miR-505 and RASSF8 was validated using dual-luciferase reporter gene assay.

KEY FINDINGS: MiR-505 expression significantly increased in resistant tissues compared with sensitive tissues. Down-regulation of miR-505 expression weakened the proliferation ability of LS174T and LS174T/MTX cells, induced cell cycle arrest and apoptosis rate. RASSF8 was a target of miR-505 and overexpression of miR-505 down-regulated RASSF8 mRNA and protein expression. Overexpression of RASSF8 could affect the cycle of CRC cells, accelerate apoptosis as well as restrain migration and invasion. Moreover, miR-505 advanced MTX-induced LS174T cells migration and invasiveness as well as depressed LS174T/MTX cell apoptosis through the down-regulation of RASSF8.

CONCLUSION: MiR-505 mediated MTX resistance, propagation, cell cycle and metastasis by targeting RASSF8 in colorectal cancer.