No abstract

Endogenous sphingolipids (ceramide) and related synthetic molecules (FTY720, SH-BC-893) reduce nutrient access by decreasing cell surface expression of a subset of nutrient transporter proteins. Here, we report that these sphingolipids disrupt endocytic recycling by inactivating the small GTPase ARF6. Consistent with reported roles for ARF6 in maintaining the tubular recycling endosome, MICAL-L1-positive tubules were lost from sphingolipid-treated cells. We propose that ARF6 inactivation may occur downstream of PP2A activation since: (1) sphingolipids that fail to activate PP2A did not reduce ARF6-GTP levels; (2) a structurally unrelated PP2A activator disrupted tubular recycling endosome morphology and transporter localization; and (3) overexpression of a phosphomimetic mutant of the ARF6 GEF GRP1 prevented nutrient transporter loss. ARF6 inhibition alone was not toxic; however, the ARF6 inhibitors SecinH3 and NAV2729 dramatically enhanced the killing of cancer cells by SH-BC-893 without increasing toxicity to peripheral blood mononuclear cells, suggesting that ARF6 inactivation contributes to the anti-neoplastic actions of sphingolipids. Taken together, these studies provide mechanistic insight into how ceramide and sphingolipid-like molecules limit nutrient access and suppress tumor cell growth and survival.

Obesity and poor diet often go hand-in-hand, altering metabolic signaling and thereby impacting breast cancer risk and outcomes. We have recently demonstrated that dietary patterns modulate mammary microbiota populations. An important and largely open question is whether the microbiome of the gut and mammary gland mediates the dietary effects on breast cancer. To address this, we performed fecal transplants between mice on control or high-fat diets (HFD) and recorded mammary tumor outcomes in a chemical carcinogenesis model. HFD induced protumorigenic effects, which could be mimicked in animals fed a control diet by transplanting HFD-derived microbiota. Fecal transplants altered both the gut and mammary tumor microbiota populations, suggesting a link between the gut and breast microbiomes. HFD increased serum levels of bacterial lipopolysaccharide (LPS), and control diet–derived fecal transplant reduced LPS bioavailability in HFD-fed animals. In vitro models of the normal breast epithelium showed that LPS disrupts tight junctions (TJ) and compromises epithelial permeability. In mice, HFD or fecal transplant from animals on HFD reduced expression of TJ-associated genes in the gut and mammary gland. Furthermore, infecting breast cancer cells with an HFD-derived microbiome increased proliferation, implicating tumor-associated bacteria in cancer signaling. In a double-blind placebo-controlled clinical trial of patients with breast cancer administered fish oil supplements before primary tumor resection, dietary intervention modulated the microbiota in tumors and normal breast tissue. This study demonstrates a link between the gut and breast that mediates the effect of diet on cancer. Significance: This study demonstrates that diet shifts the microbiome in the gut and the breast tumor microenvironment to affect tumorigenesis, and oral dietary interventions can modulate the tumor microbiota in patients with breast cancer.

Nutrient stress that produces quiescence and catabolism in normal cells is lethal to cancer cells because oncogenic mutations constitutively drive anabolism. One driver of biosynthesis in cancer cells is the mTORC1 signaling complex. Activating mTORC1 by deleting its negative regulator TSC2 leads to hypersensitivity to glucose deprivation. We have previously shown that ceramide kills cells in part by triggering nutrient transporter loss and restricting access to extracellular amino acids and glucose suggesting that TSC2-deficient cells would be hypersensitive to ceramide. However, murine embryonic fibroblasts (MEFs) lacking TSC2 were highly resistant to ceramide-induced death. Consistent with the observation that ceramide limits access to both amino acids and glucose, TSC2−/− MEFs also had a survival advantage when extracellular amino acids and glucose were both reduced. As TSC2−/− MEFs were resistant to nutrient stress despite sustained mTORC1 activity, we assessed whether mTORC1 signaling might be beneficial under these conditions. In low amino acid and glucose medium and following ceramide-induced nutrient transporter loss, elevated mTORC1 activity significantly enhanced the adaptive up-regulation of new transporter proteins for amino acids and glucose. Strikingly, the introduction of oncogenic Ras abrogated the survival advantage of TSC2−/− MEFs upon ceramide treatment most likely by increasing nutrient demand. These results suggest that, in the absence of oncogene-driven biosynthetic demand, mTORC1 dependent translation facilitates the adaptive cellular response to nutrient stress.

Despite advances in cancer therapy, several persistent issues remain. These include cancer recurrence, effective targeting of aggressive or therapy-resistant cancers, and selective treatments for transformed cells. This review evaluates the current findings and highlights the potential of targeting the unfolded protein response to treat cancer. The unfolded protein response, an evolutionarily conserved pathway in all eukaryotes, is initiated in response to misfolded proteins accumulating within the lumen of the endoplasmic reticulum. This pathway is initially cytoprotective, allowing cells to survive stressful events; however, prolonged activation of the unfolded protein response also activates apoptotic responses. This balance is key in successful mammalian immune response and inducing cell death in malignant cells. We discuss how the unfolded protein response affects cancer progression, survival, and immune response to cancer cells. The literature shows that targeting the unfolded protein response as a monotherapy or in combination with chemotherapy or immunotherapies increases the efficacy of these drugs; however, systemic unfolded protein response targeting may yield deleterious effects on immune cell function and should be taken into consideration. The material in this review shows the promise of both approaches, each of which merits further research.

The metabolism of arachidonic acid and other polyunsaturated fatty acids produces eicosanoids, a family of biologically active lipids that are implicated in homeostasis and in several pathologies that involve inflammation. Inflammatory processes mediated by eicosanoids promote carcinogenesis by exerting direct effects on cancer cells and by affecting the tumor microenvironment. Therefore, understanding how eicosanoids mediate cancer progression may lead to better approaches and chemopreventive strategies for the treatment of cancer. The matricellular protein thrombospondin-1 is involved in processes that profoundly regulate inflammatory pathways that contribute to carcinogenesis and metastatic spread. This review focuses on interactions of thrombospondin-1 and eicosanoids in the microenvironment that promote carcinogenesis and how the microenvironment can be targeted for cancer prevention to increase curative responses of cancer patients.

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<p>A. Uninfected 4T1 tumor volume from mice treated 1 x weekly control diet-derived fecal transplant. B. Uninfected 4T1 tumor volume from mice treated 1 x weekly lard diet-derived fecal transplant. C. Tumor volume over time of uninfected 4T1 cells mixed with control diet-derived fecal conditioned media infected RAW 264.7 (macrophage) cells. D. Tumor volume over time of uninfected 4T1 cells mixed with lard diet-derived fecal conditioned media infected RAW 264.7 (macrophage) cells. E. Tumor proliferation as determined by Ki67 immunoreactivity. F. Gram-positive bacteria content in 4T1 breast tumors. G. LPS positive bacteria content in 4T1 tumors. H. Infiltrating tumor-associated macrophage content in 4T1 tumors was determined by F4/80 immunoreactivity. n=5-6.*p<0.05</p>