The positivity rate for miRNA were related to adverse clinical features of primary breast cancer as high histological grading (X<sup>2</sup> = 7.72, P = 0.016), presence of metastasis to lymph node (X<sup>2</sup> = 21.8, P < 0.001), large tumor size (X<sup>2</sup> = 6.41, P = 0.041), and hormonal status (P < 0.001). miRNA-335 mean rank level was significantly different among breast cancer subtypes and its level was inferior in triple negative breast cancer.
Extracellular vesicles produced in B cells deliver tumor suppressor miR-335 to breast cancer cells disrupting oncogenic programming in vitro and in vivo.
In the present study, we used bioinformatic and biochemical analyses to demonstrate that EphA4 is a direct downstream target of miR-335 in human breast cancer MCF-7 and MDA-MB-23 cells and revealed that miR-335 negatively regulates the expression of EphA4 in these cells.
Of the 9 miRNAs, miR-30a, miR-30c, miR-126, miR-140, miR-206, and miR-335 were found to have significantly lower expression in breast cancer tissues compared to paired normal breast tissue.
In conclusion, this study provides novel insights into the in vitro regulatory patterns of miRNA-335 and PAX6 in breast cancer, and indicates that miRNA-335 may constitute a promising candidate for the treatment of breast cancer.
Based on the results obtained in the last decade, some miRNAs are emerging as biomarkers of BC for diagnosis (i.e., miR-9, miR-10b, and miR-17-5p), prognosis (i.e., miR-148a and miR-335), and prediction of therapeutic outcomes (i.e., miR-30c, miR-187, and miR-339-5p) and have important roles in the control of BC hallmark functions such as invasion, metastasis, proliferation, resting death, apoptosis, and genomic instability.
Specific miRNAs (mir-10, mir-21, mir-155, mir-373, mir-30b, mir-126, mir-17p, mir-335) are associated with tumor metastasis and other clinical characteristics for BC, facilitating identification of individuals who are at risk.
We thus implicate the miR-335 locus on 7q32.2 as the first selective metastasis suppressor and tumor initiation suppressor locus in human breast cancer.
The relevance of the miR-335 regulation for human breast cancer was confirmed in primary sporadic breast cancer specimens with significantly decreased miR-335 levels (p < 0.05) in comparison to normal controls.
Furthermore, the relative expression of miR-21, miR-126, miR-155, miR-199a and miR-335 was closely associated with clinicopathologic features of breast cancer (P < 0.05), such as histological tumor grades and sex hormone receptor expression.
Furthermore, functional studies have uncovered their roles in breast cancer as both tumour suppressor genes (eg miR-335) and oncogenes (eg miR-21). miRNAs deregulated in breast cancer influence the translational regulation of well-established regulatory molecules, such as oestrogen receptor-alpha, which is regulated by miR-206, and novel cancer-related molecules whose functions are not yet fully understood..
Of these microRNAs, miR-126 restoration reduces overall tumour growth and proliferation, whereas miR-335 inhibits metastatic cell invasion. miR-335 regulates a set of genes whose collective expression in a large cohort of human tumours is associated with risk of distal metastasis. miR-335 suppresses metastasis and migration through targeting of the progenitor cell transcription factor SOX4 and extracellular matrix component tenascin C. Expression of miR-126 and miR-335 is lost in the majority of primary breast tumours from patients who relapse, and the loss of expression of either microRNA is associated with poor distal metastasis-free survival. miR-335 and miR-126 are thus identified as metastasis suppressor microRNAs in human breast cancer.