Transcription Factor FOSL1 Enhances Drug Resistance of Breast Cancer through DUSP7-Mediated Dephosphorylation of PEA15

Breast cancer is one of the commonest malignancies in women with first occurrence and fifth mortality in the world. However, drug resistance has always been a major obstacle to cancer treatment. Transcription factors have been reported to have close association with drug resistance of tumors. Recently, by analyzing the data from Gene Expression Omnibus database (GSE76540), we found that transcription factor FOS like 1, AP-1 transcription factor subunit (FOSL1) was significantly upregulated in the transcriptome of doxorubicin-resistant breast cancer cells compared with that in sensitive parental cells. Therefore, we aim to explore the regulatory mechanism of FOSL1 in affecting the drug resistance of breast cancer cells. FOSL1 expression in doxorubicin-resistant breast cancer cells was firstly examined through qRT-PCR, and then its influence on the drug resistance of breast cancer cells was explored through a series of in vitro and in vivo mechanism assays. Results showed that FOSL1 promoted the drug resistance of breast cancer cells to doxorubicin both in intro and in vivo. It positively regulated the transcription of dual specificity phosphatase 7 (DUSP7) in breast cancer doxorubicin-resistant cells and DUSP7 also enhanced the drug resistance of breast cancer cells. Furthermore, FOSL1 promoted the dephosphorylation of proliferation and apoptosis adaptor protein 15 (PEA15) through DUSP7. In conclusion, it was verified that FOSL1 promoted the drug resistance in breast cancer through DUSP7-mediated dephosphorylation of PEA15.These initial findings suggest that the FOSL1/DUSP7/PEA15 pathway may provide a theoretical guidance for breast cancer treatment.