Abstract
MicroRNAs (miRs), a class of non-coding RNAs that are 18‑25 nucleotides in length, serve as key regulators in the development and progression of human cancers. Previously, miR‑503 has been implicated in breast cancer. However, the underlying mechanism of miR‑503 in regulating the proliferation and invasion of breast cancer cells remains largely unknown. In the present study, reverse transcription‑quantitative polymerase chain reaction analysis indicated that the expression of miR‑503 was significantly reduced in breast cancer tissues compared with their matched adjacent normal tissues. Furthermore, miR‑503 expression levels were markedly reduced in T2‑T4 stage breast cancer, compared with T1 stage. Insulin‑like growth factor 1 receptor (IGF‑1R) was further identified as a novel target of miR‑503. Overexpression of miR‑503 significantly suppressed the protein expression levels of IGF‑1R. Furthermore, it inhibited the proliferation and invasion of human breast cancer MCF‑7 cells, as assessed by MTT and Transwell assays, respectively. However, restoration of IGF‑1R expression markedly ameliorated the suppressive effects of miR‑503 overexpression on MCF‑7 cell proliferation and invasion, indicating that miR‑503 inhibits breast cancer cell proliferation and invasion at least partially via directly targeting IGF‑1R. Furthermore, the mRNA and protein expression levels of IGF‑1R were demonstrated to be significantly increased in breast cancer tissues compared with their matched adjacent normal tissues. In addition, IGF‑1R mRNA expression levels were reversely correlated with miR‑503 expression levels in breast tumors, suggesting that the upregulation of IGF‑1R may be due to downregulation of miR‑503 in breast cancer. In conclusion, the present study expanded the understanding of the regulatory mechanism of miR‑503 in breast cancer, and implicates the miR‑503/IGF‑1R axis as a potential therapeutic target for breast cancer.