MiR-99a antitumor activity in human breast cancer cells through targeting of mTOR expression.

Abstract

MicroRNAs (miRNAs) play an important role in human tumorigenesis as oncogenes or tumor suppressors. miR-99a has been reported as a tumor suppressor gene in various cancers in humans. However, only limited information about the function of miR-99a in human breast cancers is available. Here we investigated the expression of miR-99a in breast cancer tissue specimens and its antitumor activity in breast cancer cells. We initially identified that the expression of miR-99a was significantly reduced in four breast cancer cell lines. More importantly, we found downregulation of miR-99a in breast cancer specimens from ten different patients. We then analyzed the mechanism of miR-99a in inhibiting tumorigenesis. Cell-based assays that showed overexpression of miR-99a not only reduced breast cancer cell viability by inducing accumulation of cells at sub-G1 phase and cell apoptosis, but also inhibited tumorigenicity in vivo. As a critical miR-99a target, we have shown that the function of mammalian target of rapamycin (mTOR) was greatly inhibited by miR-99a-based Luciferase report assay; overexpression of miR-99a reduced the expression of mTOR and its downstream phosphorylated proteins (p-4E-BP1 and p-S6K1). Similar to restoring miR-99a expression, mTOR downregulation suppressed cell viability and increased cell apoptosis, whereas restoration of mTOR expression significantly reversed the inhibitory effects of miR-99a on the mTOR/p-4E-BP1/p-S6K1 signal pathway and the miR-99a antitumor activity. In clinical specimens and cell lines, mTOR was commonly overexpressed and its protein levels were statistically inversely correlated with miR-99a expression. Taken together, these results have demonstrated that miR-99a antitumor activity is achieved by targeting the mTOR/p-4E-BP1/p-S6K1 pathway in human breast cancer cells. This study suggests a potential therapeutic strategy to effectively control breast cancer development.

• Authors: Yu Hu, Qin Zhu, Lili Tang
• Journal: PloS one (PLoS One) Vol. 9 Issue 3 Pg. e92099 ( 2014) ISSN: 1932-6203 [Electronic] United States
• PMID: 24637915 (Publication Type: Journal Article)

Chemical References

• Adaptor Proteins, Signal Transducing
• Antineoplastic Agents
• Cell Cycle Proteins
• EIF4EBP1 protein, human
• MIRN99 microRNA, human
• MicroRNAs
• Phosphoproteins
• MTOR protein, human
• Ribosomal Protein S6 Kinases, 70-kDa
• TOR Serine-Threonine Kinases
• ribosomal protein S6 kinase, 70kD, polypeptide 1

Topics

• Adaptor Proteins, Signal Transducing (metabolism)
• Animals
• Antineoplastic Agents (metabolism)
• Apoptosis (genetics)
• Base Sequence
• Breast Neoplasms (genetics, pathology)
• Cell Cycle Proteins
• Cell Line, Tumor
• Cell Survival (genetics)
• Down-Regulation
• Female
• Gene Expression Profiling
• Gene Expression Regulation, Neoplastic
• Humans
• Mice
• MicroRNAs (genetics, metabolism)
• Molecular Sequence Data
• Phosphoproteins (metabolism)
• Phosphorylation
• Ribosomal Protein S6 Kinases, 70-kDa (metabolism)
• Signal Transduction (genetics)
• TOR Serine-Threonine Kinases (antagonists & inhibitors, genetics, metabolism)
• Up-Regulation (genetics)
• Xenograft Model Antitumor Assays