Role of c-Myc and miRNAs on EMT and the TGF-betaSwitch in Primary Intermediate Basal Cells Isolated From Prostate Cancer.

摘要

We aimed to further understand the role of c-myc and the microRNA let-7 in TGF-beta induced EMT and invasion of primary prostate cancer cells. Overexpression of c-myc in combination with TGF-beta failed to induce EMT in our cell lines. Thus, we have completed mechanistic studies with cells stably transfected with ras effector mutant constructs and constitutively activated MEK1 and MEK2 to show that ras activation of the raf-MEK2 pathway works in concert with TGF-beta to promote EMT and invasion in early stage prostate cancer cells. EMT was characterized by the adoption of a spindle shaped morphology, loss of cell-cell junctions, decreased E-cadherin and increased expression of the prometastatic genes vimentin, fibronectin, fsp-1, HMGA2 MMP-2, MMP-9, Slug and Twist2. We also discovered that EGF signaling down regulates expression of the tumor suppressor let-7a miRNA and upregulates its negative regulator, Lin28B. Activation of this pathway appeared to allow for expression of Let-7a targets which play a key role in EMT, including ras and HMGA2. Additionally, overexpression of pre-let-7a, inhibited the ability of cells to undergo EMT and become invasive. We conclude that cells require both TGF-beta stimulation and let-7a down regulation via ras-raf-MEK2 to undergo EMT and transform to an invasive phenotype. Our studies thus far have provided novel insights into the mechanisms regulating EMT and invasion in prostate cancer and assign a novel function to the tumor suppressor microRNA let-7a.