Association of miR-21 and miR-155 with regulation of 15-HPGD mRNA in human breast cancer cells

Breast cancer (BC) is the most common form of cancer, leading to high mortality rates among women worldwide. In this study we have analyzed mRNA expression of 15-hydroxy-prostaglandin-dehydrogenases (15-HPGD), cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) and miRNAs (miR-21, miR-155) in three cell lines of estrogen-positive human breast carcinomas (MCF-7, BT-474, ZR-75-1). Results of three independent experiments have demonstrated significantly higher levels of COX-2 and COX-1 mRNAs in the cell line ZR-75-1 cells than in MCF-7 and BT-474 cells. mRNA levels of total 15-HPGD and functional-15-HPGD were lower in BT-474 than in MCF-7 and in ZR-75-1 cells. Synthesis of the 15-HPGD enzyme in BT-474 cells was blocked at the level of nuclear processing of an immature pre-mRNA. High expression of miR-21 was detected in all the tumor cell lines (MCF-7, ZR-75-1 and BT-474). In the breast cancer cell lines, the expression level of miR-155 was significantly lower than that of miR-21 . Correlations have been found between dysregulation of miR-21, miR-155 and mRNA levels of 15-HPGD, COX-1, COX-2 . The results obtained in this study showed that miR-21 and miR-155 regulate activity of several genes in the tumor cell and on some genes they exhibited a cumulative effect. Based on these results, we concluded that the miR-21 and miR-155 inhibit activity of the tumor suppressor gene 15-HPGD and induce a potential oncogene COX-2 , which contributes to malignancy and metastasis of breast cancer cells.