Let‐7d miRNA Shows Both Antioncogenic and Oncogenic Functions in Osteosarcoma‐Derived 3AB‐OS Cancer Stem Cells. Issue 8 (28th January 2016) - Di Fiore, Riccardo
Abstract : Osteosarcoma (OS), an aggressive highly invasive and metastatic bone‐malignancy, shows therapy resistance and recurrence, two features that likely depend on cancer stem cells (CSCs), which hold both self‐renewing and malignant potential. So, effective anticancer therapies against OS should specifically target and destroy CSCs. We previously found that the let‐7d microRNA was downregulated in the 3AB‐OS‐CSCs, derived from the human OS‐MG63 cells. Here, we aimed to assess whether let‐7d modulation affected tumorigenic and stemness properties of these OS‐CSCs. We found that let‐7d‐overexpression reduced cell proliferation by decreasing CCND2 and E2F2 cell‐cycle‐activators and increasing p21 and p27 CDK‐inhibitors. Let‐7d also decreased sarcosphere‐and‐colony forming ability, two features associated with self‐renewing, and it reduced the expression of stemness genes, including Oct3/4, Sox2, Nanog, Lin28B, and HMGA2. Moreover, let‐7d induced mesenchymal‐to‐epithelial‐transition, as shown by both N‐Cadherin‐E‐cadherin‐switch and decrease in vimentin. Surprisingly, such switch was accompanied by enhanced migratory/invasive capacities, with a strong increase in MMP9, CXCR4 and VersicanV1. Let‐7d‐ overexpression also reduced cell sensitivity to apoptosis induced by both serum‐starvation and various chemotherapy drugs, concomitant with decrease in caspase‐3 and increase in BCL2 expression. Our data suggest that let‐7d in 3AB‐OS‐CSCs could induce plastic‐transitions from CSCs‐to‐non‐CSCs and vice‐versa. To our knowledge this is the first study to comprehensively examine the expression and functions of let‐7d in OS‐CSCs. By showing that let‐7d has both tumor suppressor and oncogenic functions in this context, our findings suggest that, before prospecting new therapeutic strategies based on let‐7d modulation, it is urgent to better define its multiple functions. J. Cell. Physiol. 231: 1832–1841, 2016. © 2015 Wiley Periodicals, Inc. Abstract : Osteosarcoma (OS) is an aggressive highly invasive and metastatic bone‐malignancy showing therapy resistance and recurrence that likely depend on cancer stem cells (CSCs). So, effective anticancer therapy against OS should destroy CSCs. We found that in the human 3AB‐OS‐CSCs, where the let‐7d microRNA was strongly downregulated, let‐7d‐overexpression decreased cell proliferation, sarcosphere‐and‐colony forming ability and the expression of stemness genes, by also inducing mesenchymal‐to‐epithelial‐transition. Surprisingly these changes were accompanied by enhanced migratory/invasive capacities suggesting that in 3AB‐OS‐CSCs let‐7d could induce plastic‐transitions from CSCs‐to‐non‐CSCs and vice‐versa. By showing that let‐7d has both tumor suppressor and oncogenic functions in this context, our findings suggest that, before prospecting new therapeutic strategies based on let‐7d modulation, it is urgent to better define its multiple functions.