miR-618: possible control over TIMP-1 and its expression in localized prostate cancer

The imbalance between the action of the tissue inhibitors of matrix metalloproteinases (TIMPs) and the matrix metalloproteinases (MMPs) is one component of metastasis physiology. TIMP-1 overrides MMP-9 activity in cancer and might be regulated by miR-618. The aims of this study were to clarify whether TIMP-1 expression is modified by miR-618 and to clarify the effect of miR-618 expression on the invasion of prostate cancer cells. We also studied miR-618 expression in surgical specimens of patients with localized prostate cancer submitted to open radical prostatectomy.

After transfection of miR-618 or its antagonist in DU145 cells, qRT-PCR for TIMP-1/MMP-9 and both ELISA and zymography for MMP-9 were performed. Total miRNA was extracted from surgical specimens of PCa, and miR-618 expression was examined for correlations with Gleason score, pathological status and biochemical recurrence.

DU145 cells transfected with miR-618 had a 76% reduction in TIMP-1 expression relative to control cells (p = 0.003). miR-618 inhibition reduced MMP-9 expression by 31% (p = 0.032) and MMP-9 absorbance evaluated with ELISA assay (p = 0.06).Zymography suggested higher MMP-9 activity in DU145 cells transfected with miR-618 than those transfected with miR-618 inhibitor, but the difference was not significant (p = 0.55). However, miR-618 expression was lower in surgical specimens of patients with Gleason score > 7 (p = 0.08) and more advanced disease (p = 0.07).

In vitro, miR-618 overexpression decreases TIMP-1 and miR-618 inhibition decreases MMP-9, suggesting that miR-618 might be an oncomiR. However, the analysis of clinical samples of localized prostate cancer revealed an inconsistent pattern, as increased miR-618 expression was associated with lower Gleason score and pathological status. Further studies are needed to address whether miR-618 is a context-dependent miRNA.