Let-7b expression determines response to chemotherapy through the regulation of Cyclin D1 in Glioblastoma

Abstract

BackgroundGlioblastoma is the most common type of primary brain tumors. Cisplatin is a commonly used chemotherapeutic agent for Glioblastoma patients. Despite a consistent rate of initial responses, cisplatin treatment often develops chemoresistance, leading to therapeutic failure. Cellular resistance to cisplatin is of great concern and understanding the molecular mechanisms is an utter need.MethodsGlioblastoma cell line U251 cells were exposed to increasing doses of cisplatin for 6 months to establish cisplatin-resistant cell line U251R. The differential miRNA expression profiles in U251 and U251R cell lines were identified by microarray analysis and confirmed by Q-PCR. MiRNA mimics were transfected into U251R cells, and cellular response to cisplatin-induced apoptosis and cell cycle distribution were examined by FACS analysis.ResultsU251R cells showed 3.1-fold increase in cisplatin resistance compared to its parental U251 cells. Microarray analysis identified Let-7b and other miRNAs significantly down-regulated in U251R cells compared to U251 cells. Transfection of Let-7b mimics greatly re-sensitized U251R cells to cisplatin, while transfection of other miRNAs has no effect or slightly effect. Cyclin D1 is predicted as a target of Let-7b through bioinformatics analysis. Over-expression of Let-7b mimics suppressed cyclin D1 protein expression and inhibited cyclin D1-3’-UTR luciferase activity. Knockdown of cyclin D1 expression significantly increased cisplatin-induced G1 arrest and apoptosis.ConclusionsCollectively, our results indicated that cisplatin treatment leads to Let-7b suppression, which in turn up-regulates cyclin D1 expression. Let-7b may serve as a marker of cisplatin resistance, and can enhance the therapeutic benefit of cisplatin in glioblastoma cells.

Let-7b overexpression leads to increased radiosensitivity of uveal melanoma cells

“…MiRNAs play important roles in animal development, cell differentiation, and metabolism, and they have been implicated in the sensitivity of tumors to chemotherapy and radiotherapy [14,17,28]. Recently, miRNAs have been shown to be among the critical regulators involved in UM progression.…”

“…In cancer cell lines, let-7 overexpression reduces cell division and inhibits cell cycle progression [21,28,30,31]. Moreover, let-7b overexpression in melanoma cells resulted in significant downregulation of cyclin D1 protein expression by targeting the 3′-UTR of cyclin D1 mRNA [30].…”

“…Cyclin D1 contains a let-7b-binding site in its 3′-UTR, and it was also reported to be a target of let-7b [28]. To further investigate the mechanism of let-7b-induced changes in radiosensitivity, we measured the expression of cyclin D1 in UM cells transfected with let-7b or anti-let7b by western blot.…”

MicroRNA-20a contributes to cisplatin-resistance and migration of OVCAR3 ovarian cancer cell line

“…Studies have suggested that aberrant miR expression levels have been associated with tumor biology, including resistance to various chemotherapeutic agents (9,10). For example, let-7b suppression induces resistance to cisplatin by the upregulation of cyclin D1 in glioblastoma (11). miRs overexpression has also been demonstrated to result in resistance to drugs in colorectal and prostate cancer (12,13).…”

Non-equivalent Roles of AGO1 and AGO2 in mRNA Turnover and Translation of Cyclin D1 mRNA

“…We previously observed that during this process, cyclin D1 (Ccnd1), a regulator of the G1 phase, is posttranscriptionally regulated by the ATP sensor mTORC1 complex acting through miR-1 and miR-26a (14). In glioblasoma cells (15) and in Respiratory Syncytial Virus (RSV) infected alveolar epithelial cells (16), Ccnd1 is regulated by Let-7 family members. The repression of Ccnd1 protein by miR-1 in mouse myoblasts has also been reported (17).…”