Knockdown of ATG4A inhibits breast cancer progression and promotes tamoxifen chemosensitivity by suppressing autophagy.

Autophagy‑related 4A (ATG4A) is an autophagy regulator. The current study investigated the role of ATG4A in the development of tamoxifen‑resistant breast cancer. ATG4A expression was assessed in tumor and adjacent normal tissue obtained from The Cancer Genome Atlas database. Analyses of the disease‑free survival between the ATG4A high and low expression groups was then evaluated in patients with breast cancer. Cell viability and apoptosis in MCF7/R cells was detected using Cell Counting Kit‑8 assay and flow cytometry, respectively. Gene set enrichment analysis identified the pathway responsible for the effects of ATG4A. The protein expression of ATG4A, LC3, p62, Bcl‑2, Bax, GSK‑3β, phosphorylated (p)‑GSK‑3β, β‑catenin, cyclinD1 and c‑myc in MCF and MCF7/R cells was determined using western blot. In this study, ATG4A expression was increased in the tumor tissues, and a higher ATG4A expression exhibited poor disease‑free survival. While 4‑hydroxytamoxifen (4‑OHT) increased ATG4A expression in MCF7 and MCF7/R cells, ATG4A expression decreased in the cells treated with 3‑methyladenine (3MA). Treatment with 4‑OHT and rapamycin (an autophagy activator) increased the LC3‑II/LC3‑I ratio, LC3 puncta number and decreased the level of p62 in MCF7/R cells. However, the effects of 4‑OHT and rapamycin were reversed by 3MA and knockdown of ATG4A, respectively. After treatment with 4‑OHT, knockdown of ATG4A suppressed proliferation, triggered apoptosis, decreased the expression of Bcl‑2, β‑catenin, cyclin D1 and c‑myc, and increased the expression of Bax and p‑GSK3β in MCF7/R cells. Moreover, SKL2001, an activator of the Wnt/β‑catenin signaling pathway, reversed the effects of ATG4A knockdown on cell viability and apoptosis in MCF7/R cells. In conclusion, the knockdown of ATG4A inhibited the anticancer effects of 4‑OHT in breast cancer.