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.