Fatty acids and breast cancer cell proliferation

Group and Basis Restricted Non-Negative Matrix Factorization and Random Forest for Molecular Histotype Classification and Raman Biomarker Monitoring in Breast Cancer

Raman spectroscopy is a non-invasive optical technique that can be used to investigate biochemical information embedded in cells and tissues exposed to ionizing radiation used in cancer therapy. Raman spectroscopy could potentially be incorporated in personalized radiation treatment design as a tool to monitor radiation response in at the metabolic level. However, tracking biochemical dynamics remains challenging for Raman spectroscopy. Here we developed a novel analytical framework by combining group and basis restricted non-negative matrix factorization and random forest (GBR-NMF-RF). This framework can monitor radiation response profiles in different molecular histotypes and biochemical dynamics in irradiated breast cancer cells. Five subtypes of; human breast cancer (MCF-7, BT-474, MDA-MB-230, and SK-BR-3) and normal cells derived from human breast tissue (MCF10A) which had been exposed to ionizing radiation were tested in this framework. Reference Raman spectra of 20 biochemicals were collected and used as the constrained Raman biomarkers in the GBR-NMF-RF framework. We obtained scores for individual biochemicals corresponding to the contribution of each Raman reference spectrum to each spectrum obtained from the five cell types. A random forest classifier was then fitted to the chemical scores for performing molecular histotype classifications (HER2, PR, ER, Ki67, and cancer versus non-cancer) and assessing the importance of the Raman biochemical basis spectra for each classification test. Overall, the GBR-NMF-RF framework yields classification results with high accuracy (>97%), high sensitivity (>97%), and high specificity (>97%). Variable importance calculated in the random forest model indicated high contributions from glycogen and lipids (cholesterol, phosphatidylserine, and stearic acid) in molecular histotype classifications.

Prevention of carcinogenesis and inhibition of breast cancer tumor burden by dietary stearate

Previous studies have shown that stearate (C18:0), a dietary long-chain saturated fatty acid, inhibits breast cancer cell neoplastic progression; however, little is known about the mechanism modulating these processes. We demonstrate that stearate, at physiological concentrations, inhibits cell cycle progression in human breast cancer cells at both the G(1) and G(2) phases. Stearate also increases cell cycle inhibitor p21(CIP1/WAF1) and p27(KIP1) levels and concomitantly decreases cyclin-dependent kinase 2 (Cdk2) phosphorylation. Our data also show that stearate induces Ras- guanosine triphosphate formation and causes increased phosphorylation of extracellular signal-regulated kinase (pERK). The MEK1 inhibitor, PD98059, reversed stearate-induced p21(CIP1/WAF1) upregulation, but only partially restored stearate-induced dephosphorylation of Cdk2. The Ras/mitogen-activated protein kinase/ERK pathway has been linked to cell cycle regulation but generally in a positive way. Interestingly, we found that stearate inhibits both Rho activation and expression in vitro. In addition, constitutively active RhoC reversed stearate-induced upregulation of p27(KIP1), providing further evidence of Rho involvement. To test the effect of stearate in vivo, we used the N-Nitroso-N-methylurea rat breast cancer carcinogen model. We found that dietary stearate reduces the incidence of carcinogen-induced mammary cancer and reduces tumor burden. Importantly, mammary tumor cells from rats on a stearate diet had reduced expression of RhoA and B as well as total Rho compared with a low-fat diet. Overall, these data indicate that stearate inhibits breast cancer cell proliferation by inhibiting key check points in the cell cycle as well as Rho expression in vitro and in vivo and inhibits tumor burden and carcinogen-induced mammary cancer in vivo.

Differential effects of palmitate and palmitoleate on insulin action and glucose utilization in rat L6 skeletal muscle cells

An increase in circulating levels of specific NEFAs (non-esterified fatty acids) has been implicated in the pathogenesis of insulin resistance and impaired glucose disposal in skeletal muscle. In particular, elevation of SFAs (saturated fatty acids), such as palmitate, has been correlated with reduced insulin sensitivity, whereas an increase in certain MUFAs and PUFAs (mono- and poly-unsaturated fatty acids respectively) has been suggested to improve glycaemic control, although the underlying mechanisms remain unclear. In the present study, we compare the effects of palmitoleate (a MUFA) and palmitate (a SFA) on insulin action and glucose utilization in rat L6 skeletal muscle cells. Basal glucose uptake was enhanced approx. 2-fold following treatment of cells with palmitoleate. The MUFA-induced increase in glucose transport led to an associated rise in glucose oxidation and glycogen synthesis, which could not be attributed to activation of signalling proteins normally modulated by stimuli such as insulin, nutrients or cell stress. Moreover, although the MUFA-induced increase in glucose uptake was slow in onset, it was not dependent upon protein synthesis, but did, nevertheless, involve an increase in the plasma membrane abundance of GLUT1 and GLUT4. In contrast, palmitate caused a substantial reduction in insulin signalling and insulin-stimulated glucose transport, but was unable to antagonize the increase in transport elicited by palmitoleate. Our findings indicate that SFAs and MUFAs exert distinct effects upon insulin signalling and glucose uptake in L6 muscle cells and suggest that a diet enriched with MUFAs may facilitate uptake and utilization of glucose in normal and insulin-resistant skeletal muscle.

Oleate promotes the proliferation of breast cancer cells via the G protein-coupled receptor GPR40

Evidence from epidemiological studies and animal models suggests a link between high levels of dietary fat intake and risk of breast cancer. In addition, obesity, in which circulating lipids are elevated, is associated with increased risk of various cancers. Relative to this point, we previously showed that oleate stimulates the proliferation of breast cancer cells and that phosphatidylinositol 3-kinase plays a role in this process. Nonetheless, questions remain regarding the precise mechanism(s) by which oleate promotes breast cancer cell growth. Pharmacological inhibitors of the GTP-binding proteins G(i)/G(o), phospholipase C, Src, and mitogenic-extracellular signal-regulated kinase 1/2 (MEK 1/2) decreased oleate-induced [3H]thymidine incorporation in the breast cancer cell line MDA-MB-231. In addition, oleate caused a rapid and transient rise in cytosolic Ca2+ and an increase in protein kinase B phosphorylation. Overexpressing in these cells the G protein-coupled receptor GPR40, a fatty acid receptor, amplified oleate-induced proliferation, whereas silencing the GPR40 gene using RNA interference decreased it. Overexpressing GPR40 in T47D and MCF-7 breast cancer cells that are poorly responsive to oleate allowed a robust proliferative action of oleate. The data indicate that the phospholipase C, MEK 1/2, Src, and phosphatidylinositol 3-kinase/protein kinase B signaling pathways are implicated in the proliferative signal induced by oleate and that these effects are mediated at least in part via the G protein-coupled receptor GPR40. The results suggest that GPR40 is implicated in the control of breast cancer cell growth by fatty acids and that GPR40 may provide a link between fat and cancer.

Oleic acid, the main monounsaturated fatty acid of olive oil, suppresses Her-2/neu (erbB-2) expression and synergistically enhances the growth inhibitory effects of trastuzumab (Herceptin) in breast cancer cells with Her-2/neu oncogene amplification

BACKGROUND

The relationship between the intake of olive oil, the richest dietary source of the monounsaturated fatty acid oleic acid (OA; 18:1n-9), and breast cancer risk and progression has become a controversial issue. Moreover, it has been suggested that the protective effects of olive oil against breast cancer may be due to some other components of the oil rather than to a direct effect of OA.

METHODS

Using flow cytometry, western blotting, immunofluorescence microscopy, metabolic status (MTT), soft-agar colony formation, enzymatic in situ labeling of apoptosis-induced DNA double-strand breaks (TUNEL assay analyses), and caspase-3-dependent poly-ADP ribose polymerase (PARP) cleavage assays, we characterized the effects of exogenous supplementation with OA on the expression of Her-2/neu oncogene, which plays an active role in breast cancer etiology and progression. In addition, we investigated the effects of OA on the efficacy of trastuzumab (Herceptin), a humanized monoclonal antibody binding with high affinity to the ectodomain of the Her-2/neu-coded p185(Her-2/neu) oncoprotein. To study these issues we used BT-474 and SKBr-3 breast cancer cells, which naturally exhibit amplification of the Her-2/neu oncogene.

RESULTS

Flow cytometric analyses demonstrated a dramatic (up to 46%) reduction of cell surface-associated p185(Her-2/neu) following treatment of the Her-2/neu-overexpressors BT-474 and SK-Br3 with OA. Indeed, this effect was comparable to that found following exposure to optimal concentrations of trastuzumab (up to 48% reduction with 20 microg/ml trastuzumab). Remarkably, the concurrent exposure to OA and suboptimal concentrations of trastuzumab (5 microg/ml) synergistically down-regulated Her-2/neu expression, as determined by flow cytometry (up to 70% reduction), immunoblotting, and immunofluorescence microscopy studies. The nature of the cytotoxic interaction between OA and trastuzumab revealed a strong synergism, as assessed by MTT-based cell viability and anchorage-independent soft-agar colony formation assays. Moreover, OA co-exposure synergistically enhanced trastuzumab efficacy towards Her-2/neu overexpressors by promoting DNA fragmentation associated with apoptotic cell death, as confirmed by TUNEL and caspase-3-dependent PARP cleavage. In addition, treatment with OA and trastuzumab dramatically increased both the expression and the nuclear accumulation of p27(Kip1), a cyclin-dependent kinase inhibitor playing a key role in the onset and progression of Her-2/neu-related breast cancer. Finally, OA co-exposure significantly enhanced the ability of trastuzumab to inhibit signaling pathways downstream of Her-2/neu, including phosphoproteins such as AKT and MAPK.

CONCLUSIONS

These findings demonstrate that OA, the main monounsaturated fatty acid of olive oil, suppresses Her-2/neu overexpression, which, in turn, interacts synergistically with anti-Her-2/neu immunotherapy by promoting apoptotic cell death of breast cancer cells with Her-2/neu oncogene amplification. This previously unrecognized property of OA offers a novel molecular mechanism by which individual fatty acids may regulate the malignant behavior of breast cancer cells and therefore be helpful in the design of future epidemiological studies and, eventually, dietary counseling.

CEACAM1 modulates epidermal growth factor receptor--mediated cell proliferation

Phosphorylation of the cell adhesion protein CEACAM1 increases insulin sensitivity and decreases insulin-dependent mitogenesis in vivo. Here we show that CEACAM1 is a substrate of the EGFR and that upon being phosphorylated, CEACAM1 reduces EGFR-mediated growth of transfected Cos-7 and MCF-7 cells in response to EGF. Using transgenic mice overexpressing a phosphorylation-defective CEACAM1 mutant in liver (L-SACC1), we show that the effect of CEACAM1 on EGF-dependent cell proliferation is mediated by its ability to bind to and sequester Shc, thus uncoupling EGFR signaling from the ras/MAPK pathway. In L-SACC1 mice, we also show that impaired CEACAM1 phosphorylation leads to ligand-independent increase of EGFR-mediated cell proliferation. This appears to be secondary to visceral obesity and the metabolic syndrome, with increased levels of output of free fatty acids and heparin-binding EGF-like growth factor from the adipose tissue of the mice. Thus, L-SACC1 mice provide a model for the mechanistic link between increased cell proliferation in states of impaired metabolism and visceral obesity.