Breast cancer metastasis suppressor 1 up-regulates miR-146, which suppresses breast cancer metastasis - PubMed (original) (raw)

Breast cancer metastasis suppressor 1 up-regulates miR-146, which suppresses breast cancer metastasis

Douglas R Hurst et al. Cancer Res. 2009.

Abstract

Breast cancer metastasis suppressor 1 (BRMS1) is a predominantly nuclear protein that differentially regulates expression of multiple genes, leading to suppression of metastasis without blocking orthotopic tumor growth in multiple human and murine cancer cells of diverse origins. We hypothesized that miR-146 may be involved in the ability of BRMS1 to supress metastasis because miR-146 expression is altered by BRMS1 and because BRMS1 and miR-146 are both associated with decreased signaling through the nuclear factor-kappaB pathway. BRMS1 significantly up-regulates miR-146a by 6- to 60-fold in metastatic MDA-MB-231 and MDA-MB-435 cells, respectively, and miR-146b by 40-fold in MDA-MB-435 as measured by real-time quantitative reverse transcription-PCR. Transduction of miR-146a or miR-146b into MDA-MB-231 down-regulated expression of epidermal growth factor receptor, inhibited invasion and migration in vitro, and suppressed experimental lung metastasis by 69% and 84%, respectively (mean +/- SE: empty vector = 39 +/- 6, miR-146a = 12 +/- 1, miR-146b = 6 +/- 1). These results further support the recent notion that modulating the levels of miR-146a or miR-146b could have a therapeutic potential to suppress breast cancer metastasis.

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Figures

Figure 1

Figure 1

BRMS1 up-regulates miR-146. A, ectopic expression of BRMS1 in MDA-MB-231 or MDA-MB-435 breast cancer cell lines significantly enhanced the expression of miR-146a as shown by real-time RT-PCR (∼6-fold and ∼60-fold, respectively). miR-146b expression was also increased in MDA-MB-435 (∼40-fold). B, endogenous expression levels of miR-146a and miR-146b in multiple breast-derived cell lines generally show decreased levels in tumorigenic but weakly/nonmetastatic cell lines (MCF7, T47D, and MDA-MB-436) compared with the immortalized, nontumorigenic breast epithelial cell line (MCF10A) and a further decrease was found in metastatic MDA-MB-435. Please note scale differences.

Figure 2

Figure 2

EGFR protein expression is decreased by miR-146. A, EGFR is a predicted target of miR-146a and miR-146b. The EGFR target sequence is located in the 3′ UTR (numbering is based on accession number NG_007726). Solid lines indicate binding sites and dashed lines represent low-affinity T-G matches. B, ectopic expression of miR-146a or miR-146b in MDA-MB-231 resulted in a ∼50% reduction in EGFR protein levels as measured by immunoblot and densitometry.

Figure 3

Figure 3

Metastasis is suppressed by miR-146. MDA-MB-231 cells expressing human miR-146a or miR-146b or vector only were injected into the lateral tail vein of athymic mice and the lungs were analyzed for macroscopic metastases. The data are shown graphically with black dots representing the number of pulmonary metastases from each mouse, the box represents the 10th and 90th percentile, and the black line is the mean for each group. The table lists the incidence and the mean number of pulmonary metastases. Representative images for each group are pictured with arrows highlighting some of the individual lung metastases.

Figure 4

Figure 4

Working model for BRMS1-miR-146 axes in metastasis suppression. BRMS1 directly down-regulates transcription of EGFR (13), a predicted target of miR-146. Ectopic expression of miR-146a or miR-146b in cells that do not express BRMS1 has ∼50% lower EGFR. BRMS1 may regulate CXCR4 directly or via miR-146. Both EGFR and CXCR4 correlate with increased metastasis. miR-146 up-regulation by BRMS1 could be direct or indirect (by affecting NF-κB). However, the connection through NF-κB is paradoxical with a negative feedback loop described for NF-κB and miR-146a in response to inflammatory stimulation (11).

References

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