miR-1204 promotes tumor development in breast and ovarian cancer cell lines

Introduction: Amplification at chromosome 8q24 is one of the most frequent genomic abnormalities in human cancers and is associated with reduced survival duration in breast and ovarian cancers. The minimal amplified region encodes c-MYC and the non-coding RNA, PVT1 including miR-1204 encoded in exon 1b. Here we analyzed the genomic changes at chromosome 8q24.21 in breast cancer and the functional roles of miR-1204 in breast and ovarian cancer progression. Methods: The genomic changes at chromosome 8q24.21 were detected in 997 breast cancer tumors and 40 breast cancer cell lines. Expression of miR-1204 in breast and ovarian cancer cell lines was investigated by qRT-PCR method. The role of miR-1204 in the tumorigenesis of breast and ovarian cancer was explored using both knockdown and overexpression of miR-1204 in vitro. Candidate miR-1204 target genes from two independent expression microarray datasets and computational predict programs were identified and further validated by qRT-PCR and western blot methods. The role of inhibition of miR-1204 on tamoxifen sensitivity in breast cancer cells was also investigated. Results: MiR-1204 is frequently co-amplified with MYC and expression of miR-1204 is strongly correlated with the expression and amplification of the noncoding PVT1 transcript and less so with MYC in human breast and ovarian cancer cells. Inhibition of miR-1204 decreases cell proliferation and increased apoptosis in breast and ovarian cancer cell lines with 8q24 amplification, but not in lines without amplification and so may be involved in Myc-induced apoptosis. Additionally, overexpression of miR-1204 enhances both breast and ovarian cancer cell growth and Myc-initiated Rat1A cell transformation. Computational and experimental analyses 30 promising candidate miR-1204 target genes. mRNA levels for these genes were assessed after over expression and knockdown of miR-1204 as were protein levels for 10 genes for which antibodies were available. These studies implicated VDR and ESR1 as miR-1204 targets. Inhibition of miR-1204 increased response to tamoxifen in Estrogen Receptor negative breast cancer cell lines. Conclusions: We conclude that amplification of miR-1204 contributes to breast and ovarian pathophysiology at least in part, by increasing proliferation and down regulating apoptosis and by decreasing expression of VDR and ESR1.

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