ABSTRACT
Elevated O-GlcNAcylation is associated with disease states such as diabetes and cancer. O-GlcNAc transferase (OGT) is elevated in multiple cancers and inhibition of this enzyme genetically or pharmacologically inhibits oncogenesis. Here we show that O-GlcNAcylation modulates lipid metabolism in cancer cells. OGT regulates expression of the master lipid regulator the transcription factor sterol regulatory element binding protein 1 (SREBP-1) and its transcriptional targets both in cancer and lipogenic tissue. OGT regulates SREBP-1 protein expression via AMP-activated protein kinase (AMPK). SREBP-1 is critical for OGT-mediated regulation of cell survival and of lipid synthesis, as overexpression of SREBP-1 rescues lipogenic defects associated with OGT suppression, and tumor growth in vitro and in vivo. These results unravel a previously unidentified link between O-GlcNAcylation, lipid metabolism and the regulation of SREBP-1 in cancer and suggests a crucial role for O-GlcNAc signaling in transducing nutritional state to regulate lipid metabolism.
Subject(s)
Biomarkers, Tumor/metabolism , Breast Neoplasms/metabolism , Breast Neoplasms/pathology , Gene Expression Regulation, Neoplastic , Lipogenesis , N-Acetylglucosaminyltransferases/metabolism , Sterol Regulatory Element Binding Protein 1/metabolism , Animals , Apoptosis , Biomarkers, Tumor/genetics , Breast Neoplasms/genetics , Cell Proliferation , Female , Humans , Lipids/analysis , Mice , Mice, Nude , N-Acetylglucosaminyltransferases/genetics , Nutrients/metabolism , Signal Transduction , Sterol Regulatory Element Binding Protein 1/genetics , Tumor Cells, Cultured , Xenograft Model Antitumor AssaysABSTRACT
ErbB2 is frequently highly expressed in premalignant breast cancers, including ductal carcinoma in situ (DCIS); however, little is known about the signals or pathways it contributes to progression into the invasive/malignant state. Radiotherapy is often used to treat early premalignant lesions regardless of ErbB2 status. Here, we show that clinically relevant doses of ionizing radiation (IR)-induce cellular invasion of ErbB2-expressing breast cancer cells, as well as MCF10A cells overexpressing ErbB2. ErbB2-negative breast cancer cells, such as MCF7 and T47D, do not invade following treatment with IR nor do MCF10A cells overexpressing epidermal growth factor receptor. ErbB2 becomes phosphorylated at tyrosine 877 in a dose- and time- dependent manner following exposure to X-rays, and activates downstream signaling cascades including PI3K/Akt. Inhibition of these pathways, as well as inhibition of reactive oxygen species (ROS) with antioxidants, prevents IR-induced invasion. Activation of ErbB2-dependent signaling results in upregulation of the forkhead family transcription factor, FoxM1, and its transcriptional targets, including matrix metalloproteinase 2 (MMP2). Inhibition of FoxM1 by RNA interference prevented induction of invasion by IR, and overexpression of FoxM1 in MCF10A cells was sufficient to promote IR-induced invasion. Moreover, we found that 14-3-3ζ is also upregulated by IR in cancer cells in a ROS-dependent manner, is required for IR-induced invasion in ErbB2-positive breast cancer cells and together with FoxM1 is sufficient for invasion in ErbB2-negative breast cancer cells. Thus, our data show that IR-mediated activation of ErbB2 and induction of 14-3-3ζ collaborate to regulate FoxM1 and promote invasion of breast cancer cells and furthermore, may serve as therapeutic targets to enhance radiosensitivity of breast cancers.
