Evelien Rysman

De novo Lipogenesis Protects Cancer Cells from Free Radicals and Chemotherapeutics by Promoting Membrane Lipid Saturation

Activation of de novo lipogenesis in cancer cells is increasingly recognized as a hallmark of aggressive cancers and has been implicated in the production of membranes for rapid cell proliferation. In the current report, we provide evidence that this activation has a more profound role. Using a mass spectrometry-based phospholipid analysis approach, we show that clinical tumor tissues that display the lipogenic phenotype show an increase in the degree of lipid saturation compared with nonlipogenic tumors. Reversal of the lipogenic switch in cancer cells by treatment with the lipogenesis inhibitor soraphen A or by targeting lipogenic enzymes with small interfering RNA leads to a marked decrease in saturated and mono-unsaturated phospholipid species and increases the relative degree of polyunsaturation. Because polyunsaturated acyl chains are more susceptible to peroxidation, inhibition of lipogenesis increases the levels of peroxidation end products and renders cells more susceptible to oxidative stress-induced cell death. As saturated lipids pack more densely, modulation of lipogenesis also alters lateral and transversal membrane dynamics as revealed by diffusion of membrane-targeted green fluorescent protein and by the uptake and response to doxorubicin. These data show that shifting lipid acquisition from lipid uptake toward de novo lipogenesis dramatically changes membrane properties and protects cells from both endogenous and exogenous insults. These findings provide important new insights into the role of de novo lipogenesis in cancer cells, and they provide a rationale for the use of lipogenesis inhibitors as antineoplastic agents and as chemotherapeutic sensitizers.

Lipoprotein lipase links dietary fat to solid tumor cell proliferation.

Many types of cancer cells require a supply of fatty acids (FA) for growth and survival, and interrupting de novo FA synthesis in model systems causes potent anticancer effects. We hypothesized that, in addition to synthesis, cancer cells may obtain preformed, diet-derived FA by uptake from the bloodstream. This would require hydrolytic release of FA from triglyceride in circulating lipoprotein particles by the secreted enzyme lipoprotein lipase (LPL), and the expression of CD36, the channel for cellular FA uptake. We find that selected breast cancer and sarcoma cells express and secrete active LPL, and all express CD36. We further show that LPL, in the presence of triglyceride-rich lipoproteins, accelerates the growth of these cells. Providing LPL to prostate cancer cells, which express low levels of the enzyme, did not augment growth, but did prevent the cytotoxic effect of FA synthesis inhibition. Moreover, LPL knockdown inhibited HeLa cell growth. In contrast to the cell lines, immunohistochemical analysis confirmed the presence of LPL and CD36 in the majority of breast, liposarcoma, and prostate tumor tissues examined (n = 181). These findings suggest that, in addition to de novo lipogenesis, cancer cells can use LPL and CD36 to acquire FA from the circulation by lipolysis, and this can fuel their growth. Interfering with dietary fat intake, lipolysis, and/or FA uptake will be necessary to target the requirement of cancer cells for FA. Mol Cancer Ther; 10(3); 427–36. ©2011 AACR.

Aberrant activation of fatty acid synthesis suppresses primary cilium formation and distorts tissue development

Aberrant activation of fatty acid synthesis is a key feature of many advanced human cancers. Unlike in classical lipogenic tissues, this process has been implicated in membrane production required for rapid cell proliferation. Here, to gain further insight into the consequences of tumor-associated fatty acid synthesis, we have mimicked the lipogenic phenotype of cancer cells in Xenopus embryos by microinjection of RNA encoding the lipogenic transcription factor sterol regulatory element binding protein 1c (SREBP1c). Dramatic morphologic changes were observed that could be linked to alterations in Wnt and Hedgehog signaling, and ultimately to a distortion of the primary cilium. This is a sophisticated microtubular sensory organelle that is expressed on the surface of nearly every cell type and that is lost in many cancers. SREBP1c-induced loss of the primary cilium could be confirmed in mammalian Madin-Darby canine kidney (MDCK) cells and was mediated by changes in the supply of fatty acids. Conversely, inhibition of fatty acid synthesis in highly lipogenic human prostate cancer cells restored the formation of the primary cilium. Lipid-induced ciliary loss was associated with mislocalization of apical proteins, distortion of cell polarization, and aberrant epithelial tissue development as revealed in three-dimensional cultures of MDCK cells and in the developing mouse prostate. These data imply that tumor-associated lipogenesis, in addition to rendering cells more autonomous in terms of lipid supply, disturbs cilium formation and contributes to impaired environmental sensing, aberrant signaling, and distortion of polarized tissue architecture, which are all hallmarks of cancer.

Abstract 1256: A role for lipoprotein lipase in fatty acid acquisition by breast, prostate and liposarcoma tumors

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL The importance of de novo fatty acid (FA) synthesis for tumor cell growth is well established, and we have now examined the hypothesis that the uptake of exogenous FA provides an alternative FA fuel source for tumors. Background: Many tumor cells utilize FA as a major energy source, and they do not survive if the supply is interrupted. In order to obtain lipids, tumors can synthesize fatty acids from glucose-derived precursors using fatty acid synthase (FASN), or they could potentially hydrolyze diet-derived triglycerides from circulating lipoproteins using the enzyme lipoprotein lipase (LPL), and take up the free fatty acids using the cell surface channel CD36. It is also conceivable that they could obtain lipids by receptor-mediated endocytosis, using syndecan (Sdc1) and LPL. The latter two of these three mechanisms have not been examined. Methods: We employed cDNA microarray and quantitative RT-PCR to study mRNA expression, measured secreted LPL enzyme activity, and produced a monoclonal antibody for LPL protein analysis and immunohistochemistry (IHC). We also assessed cellular uptake of fluorescently labeled very low density lipoproteins (VLDL). We studied cell lines and/or tumor tissues for expression of FASN, Spot 14 (a nuclear protein that drives FASN expression), LPL, CD36, and Sdc1. Results: 1. By RT-PCR, FASN and Spot14, a driver of FASN gene expression, are expressed in all cell lines (45 breast cancer, 1 liposarcoma, 1 cervical carcinoma, 3 prostate cancer) and tumor tissues (160 breast cancer, 24 liposarcoma, 10 prostate cancer) examined. 2. By RT-PCR and enzyme activity assays, LPL is expressed only in liposarcoma and triple-negative breast cancer cell lines. Prostate cancer cells secrete negligible LPL. 3. Addition of exogenous LPL and triglyceride substrate to culture media enhanced the growth of breast cancer and liposarcoma cell lines, but not prostate cancer cell lines. 4. Provision of exogenous LPL, however, rescued prostate cancer cell lines from the cytotoxicity of FASN inhibition. 5. siRNA-mediated knockdown of LPL impaired the growth of HeLa cells, 6. In contradistinction to observations in cell lines, IHC demonstrated brisk expression of LPL in all liposarcomas, prostate tumors, and breast cancer tumors examined, irrespective of ER/PR or HER2/neu status. 7. CD36 is expressed in the majority of tumors examined by IHC, including 98% of breast cancers. 8. Sdc1 and CD36 are expressed in triple-negative DU4475 breast cancer cells, but they did not endocytose labeled VLDL particles. Conclusions: These data demonstrate that, in addition to de novo FA synthesis, tumors can utilize diet-derived fat, and that this can fuel their growth. Our findings provide a mechanism, namely lipolysis by LPL and uptake by CD36, for the link between dietary fat intake and tumor progression. Inhibition of lipolysis, as well as lipogenesis, may be a necessary strategy to target the FA requirement of aggressive tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1256. doi:10.1158/1538-7445.AM2011-1256