Phosphoproteome Analysis Reveals Estrogen-ER pathway as a modulator of mTOR activity via DEPTOR

Journal Article · Thu Aug 01 04:00:00 EDT 2019 · Molecular and Cellular Proteomics

DOI:https://doi.org/10.1074/mcp.RA119.001506· OSTI ID:1599101

Cuesta, Rafael ^[1]; Gritsenko, Marina A. ^[2]; Petyuk, Vladislav A. ^[2]; Shukla, Anil K. ^[2]; Tsai, Chia-Feng ^[2]; Liu, Tao ^[2]; McDermott, Jason E. ^[2]; Holz, Marina ^[3]

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1. New York Medical College
2. BATTELLE (PACIFIC NW LAB)
3. Albert Einstein Cancer Center

ER-positive breast tumors represent approximately 70% of all breast cancer cases. Although their treatment with endocrine therapies is effective in the adjuvant or recurrent settings, the development of resistance compromises their effectiveness. The binding of estrogen to ERa, a transcription factor, triggers the regulation of the target genes (genomic pathway). Additionally, a cytoplasmic fraction of estrogen-bound ERa activates oncogenic signaling pathways such as PI3K/AKT/mTOR (nongenomic pathway). The upregulation of the estrogenic and the PI3K/AKT/mTOR signaling pathways are frequently associated with a poor outcome. To better characterize the connection between these two pathways, we performed a phosphoproteome analysis of ER-positive MCF7 breast cancer cells treated with estrogen or estrogen and the mTORC1 inhibitor rapamycin. Many proteins were identified as estrogen-regulated mTORC1 targets and among them, DEPTOR was selected for further characterization. DEPTOR binds to mTOR and inhibits the kinase activity of both mTOR complexes mTORC1 and mTORC2, but mitogen-activated mTOR promotes phosphorylation-mediated DEPTOR degradation. Although estrogen enhances the phosphorylation of DEPTOR by mTORC1, DEPTOR levels increase in estrogen-stimulated cells. We demonstrated that DEPTOR accumulation is the result of estrogen-ERa-mediated transcriptional upregulation of DEPTOR expression. Consequently, the elevated levels of DEPTOR partially counterbalance the estrogen-induced activation of mTORC1 and mTORC2. These results underscore the critical role of estrogen-ERa as a modulator of the PI3K/AKT/mTOR signaling pathway in ER-positive breast cancer cells. Additionally, these studies provide evidence supporting the use of dual PI3K/mTOR or dual mTORC1/2 inhibitors in combination with endocrine therapies as a first-line treatment option for the patients with ER-positive advanced breast cancer.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1599101
• Report Number(s): PNNL-SA-145628
• Journal Information: Molecular and Cellular Proteomics, Journal Name: Molecular and Cellular Proteomics Journal Issue: 8 Vol. 18; ISSN 1535-9476
• Publisher: American Society for Biochemistry and Molecular Biology
• Country of Publication: United States
• Language: English