MicroRNA-510 mediated negative regulation of Caveolin-1 in fibroblasts promotes aggressive tumor growth.

Introduction: In the US, despite the recent decline in breast cancer deaths, a persistent mortality disparity exists between black and white women with breast cancer, with black women having a 41% higher death rate. Several studies are now reporting that racial disparities can exist independent of socioeconomic and standard of care issues, suggesting that biological factors may be involved. Caveolin-1 (Cav1) loss in the tumor stromal compartment is a novel clinical biomarker for predicting poor outcome in breast cancer including triple negative subtype, however the mechanism of Cav1 loss is unknown. We previously identified miR-510-5p as a novel oncomir and propose here that the high levels observed in patients is a novel mechanism leading to stromal Cav1 loss and worse outcomes. Methods: Cav1 was identified as a direct target of miR-510-5p through luciferase, western blot and qPCR assays. Stromal cross talk between epithelial cells and fibroblasts was assessed in vitro using transwell co-culture assays and in vivo using xenograft assays. Results: We found that Cav1 is a direct target of miR-510-5p and that expression in fibroblasts results in an 'activated' phenotype. We propose that this could be important in the context of cancer disparities as we also observed increased levels of circulating miR-510-5p and reduced levels of stromal Cav1 in black women compared to white women with breast cancer. Finally, we observed a significant increase in tumor growth when tumor cells were co-injected with miR-510-5p expressing cancer associated fibroblasts in vivo. Conclusion: We propose that miR-510-5p mediated negative regulation of Cav1 in fibroblasts is a novel mechanism of aggressive tumor growth and may be a driver of breast cancer disparity.

MicroRNA-510 promotes cell and tumor growth by targeting peroxiredoxin1 in breast cancer.

INTRODUCTION: MicroRNAs are small non-coding RNAs that are involved in the post-transcriptional negative regulation of mRNAs. MicroRNA 510 (miR-510) was initially shown to have a potential oncogenic role in breast cancer by the observation of its elevated levels in human breast tumor samples when compared to matched non-tumor samples. Few targets have been identified for miR-510. However, as microRNAs function through the negative regulation of their direct targets, the identification of those targets is critical for the understanding of their functional role in breast cancer. METHODS: Breast cancer cell lines were transfected with pre-miR-510 or antisense miR-510 and western blotting and quantitative real time PCR were performed. Functional assays performed included cell growth, migration, invasion, colony formation, cytotoxicity and in vivo tumor growth. We performed a PCR assay to identify novel direct targets of miR-510. The study focused on peroxiredoxin 1 (PRDX1) as it was identified through our screen and was bioinformatically predicted to contain a miR-510 seed site in its 3' untranslated region (3'UTR). Luciferase reporter assays and site-directed mutagenesis were performed to confirm PRDX1 as a direct target. The Student's two-sided, paired t-test was used and a P-value less than 0.05 was considered significant. RESULTS: We show that miR-510 overexpression in non-transformed and breast cancer cells can increase their cell growth, migration, invasion and colony formation in vitro. We also observed increased tumor growth when miR-510 was overexpressed in vivo. We identified PRDX1 through a novel PCR screen and confirmed it as a direct target using luciferase reporter assays. The reintroduction of PRDX1 into breast cancer cell lines without its regulatory 3'UTR confirmed that miR-510 was mediating its migratory phenotype at least in part through the negative regulation of PRDX1. Furthermore, the PI3K/Akt pathway was identified as a positive regulator of miR-510 both in vitro and in vivo. CONCLUSIONS: In this study, we provide evidence to support a role for miR-510 as a novel oncomir. We show that miR-510 directly binds to the 3'UTR of PRDX1 and blocks its protein expression, thereby suppressing migration of human breast cancer cells. Taken together, these data support a pivotal role for miR-510 in breast cancer progression and suggest it as a potential therapeutic target in breast cancer patients.