HINT3 suppresses AKT/mTOR signaling pathway activity during breast cancer tumorigenesis through PTEN transcriptional activation

Histidine triad nucleotide-binding protein (HINT) belongs to the histidine triad protein family. Recent studies have demonstrated that HINT1 and HINT2 both play a pivotal role in cancer growth. However, the functions of HINT3 in various types of cancer, including breast cancer (BRCA), have not yet been fully elucidated. In the present study, the role of HINT3 in BRCA was investigated. Based on The Cancer Genome Atlas and reverse transcription-quantitative PCR analyses, HINT3 was found to be decreased in BRCA tissues. In vitro, HINT3 knockdown promoted the proliferation and colony formation of, and 5-ethynyl-2 '-deoxyuridine incorporation in MCF-7 and MDA-MB-231 BRCA cells. By contrast, HINT3 overexpression suppressed DNA synthesis and the proliferation of both cell lines. Apoptosis was also found to be modulated by HINT3. In vivo, HINT3 ectopic expression attenuated the tumorigenesis of MDA-MB-231 and MCF-7 cells in a mouse tumor xenograft model. Furthermore, HINT3 silencing or overexpression also enhanced or inhibited, respectively, the migratory capacity of the MCF-7 and MDA-MB-231 cells. Finally, HINT3 upregulated phosphatase and tensin homolog (PTEN) at the transcriptional level, which resulted in the inactivation of AKT/mammalian target of rapamycin (mTOR) signaling both in vitro and in vivo. Taken together, the present study demonstrates that HINT3 inhibits the activation of the PTEN/AKT/mTOR signaling pathway, and suppresses the proliferation, growth, migration and tumor development of MCF-7 and MDA-MB-231 BRCA cells.