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    mTOR complex-2 stimulates acetyl-CoA and de novo lipogenesis through ATP citrate lyase in HER2/PIK3CA-hyperactive breast cancer

    Yaqing Chen, Jianchang Qian, Qun He, Hui Zhao, Lourdes Toral-Barza, Celine Shi, Xuesai Zhang, Jiang Wu and Ker Yu
    Oncotarget. 2016 May 3; 7(18): 25224–25240.
    PMID: 27015560 DOI: 10.18632/oncotarget.8279
    AZD8055(CAS:1009298-09-2);  WYE-125132(CAS:1144068-46-1);  Lapatinib(CAS:231277-92-2);  PI-103(CAS:371935-74-9);  Rapamycin(CAS:53123-88-9);  GDC-0941(CAS:957054-30-7);  

    ABSTRACT The mechanistic target of rapamycin (mTOR) is a major regulator of cell growth and is frequently dysregulated in cancer. While mTOR complex-1 (mTORC1) is a validated cancer target, the role of mTOR complex-2 (mTORC2) remains less defined. Here, we reveal mTORC2 as a critical regulator of breast cancer metabolism. We showed that hyperphosphorylation in ATP citrate lyase (ACL) occurs frequently in human breast tumors and correlates well with HER2+ and/or PIK3CA-mutant (HER2+/PIK3CAmut) status in breast tumor cell lines. In HER2+/PIK3CAmut cells, mTORC2 controls Ser-455 phosphorylation of ACL thereby promoting acetyl-CoA production, de novo lipogenesis and mitochondrial physiology, all of which were inhibited by an mTORC1/mTORC2 kinase inhibitor (mTOR-KI) or cellular depletion of mTORC2 or ACL. mTOR-KI but not rapamycin blocked the IGF-1-induced ACL phosphorylation and glucose to lipid conversion. Depletion of mTORC2 but not mTORC1 specifically inhibited the ACL-dependent acetyl-CoA production. In the HER2+/PIK3CAmut MDA361, MDA453, BT-474 and T47D cells, depletion of mTORC2 or ACL led to growth inhibition and mitochondrial hyperpolarization, which were partially rescued by an alternate source of acetyl-CoA. These same changes were not apparent in mTORC2- or ACL-depleted HER2-/PIK3CAwt MDA231 and HCC1806 cells, highlighting a differential dependence of mTORC2-ACL for survival in these two cell types. Moreover, ACL Ser-455 mutants S455E (phosphomimetic) and S455A (non-phosphorylatable) each increased or decreased, respectively, the acetyl-CoA production, mitochondrial homeostasis and survival in ACL-depleted MDA453 cells. These studies define a new and rapamycin-resistant mechanism of mTORC2-ACL in lipogenesis and acetyl-CoA biology and provide a rationale for targeting of mTORC1 and mTORC2 in HER2+/PIK3CAmut breast cancer.

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