Elsevier

European Journal of Cancer

Volume 42, Issue 15, October 2006, Pages 2425-2432
European Journal of Cancer

Short Communication
A genomic explanation connecting “Mediterranean diet”, olive oil and cancer: Oleic acid, the main monounsaturated Fatty acid of olive oil, induces formation of inhibitory “PEA3 transcription factor-PEA3 DNA binding site” complexes at the Her-2/neu (erbB-2) oncogene promoter in breast, ovarian and stomach cancer cells

https://doi.org/10.1016/j.ejca.2005.10.016Get rights and content

Abstract

Olive oil is an integral ingredient of the “Mediterranean diet” and accumulating evidence suggests that it may have a potential role in lowering risk of several cancers. We recently hypothesized that the anti-cancer actions of olive oil may relate to its monounsaturated fatty acid (MUFA) oleic acid (OA; 18:1n  9) content to specifically regulate oncogenes. In this study, transient transfection experiments with human Her-2/neu promoter-driven luciferase gene established the ability of OA to specifically repress the transcriptional activity of Her-2/neu gene. Gene repression was seen in tumour-derived cell lines with Her-2/neu gene amplification and overexpression, including SK-Br3 (⩽56% reduction), SK-OV3 (⩽75% reduction) and NCI-N87 (55% reduction) breast, ovarian and stomach cancer cell lines, respectively. Also marginal decreases in promoter activity were observed in cancer cells expressing physiological levels of Her-2/neu (⩽20% reduction in MCF-7 breast cancer cells). Remarkably, OA treatment in Her-2/neu-overexpressing cancer cells was found to induce up-regulation of the Ets protein polyomavirus enhancer activator 3 (PEA3), a transcriptional repressor of Her-2/neu promoter. Also, an intact PEA3 DNA-binding-site at endogenous Her-2/neu gene promoter was essential for OA-induced repression of this gene. Moreover, OA treatment failed to decrease Her-2/neu protein levels in MCF-7/Her2-18 transfectants, which stably express full-length human Her-2/neu cDNA controlled by a SV40 viral promoter. OA-induced transcriptional repression of Her-2/neu through the action of PEA3 protein at the promoter level may represent a novel mechanism linking “Mediterranean diet” and cancer.

Introduction

The relationship between olive oil intake and cancer risk has become a controversial issue that could have very important repercussions for human health. Different studies have shown that the consumption of olive oil may have a potential role in lowering the risk of malignant neoplasms, especially breast and stomach cancer; and also in ovary, colon and endometrium cancer 1, 2, 3, 4, 5, 6, 7, 8, 9, 10. However, the mechanisms by which the effects of olive oil are mediated are not well understood. One of the remaining concerns, before going for a causal interpretation of the inverse relation between olive oil intake and cancer risk, is to establish definitely if olive oil-related anti-cancer effects can be explained by its monounsaturated fatty acid (MUFA) content (i.e., high levels of the ω-9 MUFA oleic acid) or the antioxidant components of the unsaponifiable fraction 11.

Since cancer development and progression is believed to be a multi-step process, we recently hypothesized that a novel molecular explanation for the anti-cancer actions of olive oil may relate to the ability of oleic acid (OA; 18:1n  9) to specifically regulate key cancer-related oncogenes 12. Supporting our hypothesis, exogenous supplementation of cultured breast cancer cells with OA was found to significantly down-regulate the expression of Her-2/neu 13, a well-characterized oncogene (also called neu or erbB-2) that plays a key role in the etiology, progression and chemosensitivity of various types of human cancer 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26. These anti-Her-2/neu properties of OA offered a previously unknown molecular mechanism by which olive oil may regulate the malignant behavior of breast cancer cells. These findings generated intense public interest, since no toxicities have been reported or suspected with OA, and suggested that supplementation with OA may represent a promising dietary intervention for the prevention and/or management of Her-2/neu-related breast carcinomas 27, 28. However, two major questions remained to be addressed: (1) What is the molecular mechanism linking tumour cells’ response to OA and Her-2/neu gene expression? and (2) Is the ability of OA to down-regulate Her-2/neu a common mechanism relevant to other types of cancer other than breast cancer?

Although overexpression of Her-2/neu both in tumours and in derived cell lines was originally attributed solely to amplification of the erbB-2 gene (usually 2- to 10-fold), an elevation in Her-2/neu mRNA levels per gene copy is also observed in all the cell lines examined exhibiting gene amplification 29. This indicates that overexpression of the gene precedes and increases the likelihood of gene amplification. Indeed, an increase in transcription rate sufficient to account for the degree of overexpression has been shown in a number of Her-2/neu-overexpressing cancer cell lines 30. Our current experiments sought to characterize the effects of OA treatment on the transcription rate of Her-2/neu gene. We have also addressed if the ability of OA to down-regulate Her-2/neu is a common mechanism of OA action towards tumour types reported to exhibit Her-2/neu overexpression, including breast, ovarian and gastric carcinomas. We report that OA promoted the up-regulation of the potent trans-repressor of the human Her-2/neu gene promoter PEA3 and could account in part the ability of OA to suppress Her-2/neu overexpression in cancer cells. These findings represent a novel genomic explanation linking “Mediterranean diet” and cancer, as OA-induced transcriptional repression of Her-2/neu gene seems to equally operate in various types of human malignancies previously shown to be influenced by olive oil consumption such as breast, ovarian and stomach carcinomas.

Section snippets

Materials

Phenol red-containing improved minimal essential medium (IMEM) was from Biofluids (Rockville, MD, USA). Oleic acid (18:1n  9) was purchased from Sigma Chemical Co. (St. Louis, Missouri, USA). The cultures were supplemented, where indicated, with fatty acid-free bovine serum albumin (FA-free BSA; 0.1 mg/ml) complexed with a specific concentration of OA. A BSA-OA concentrated (100×) solution was formed by mixing 1 ml BSA (10 mg/ml) with various volumes (1–10 μl) of OA (200 mg/ml) in ethanol. The

Exogenous supplementation with OA inhibits Her-2/neu gene promoter activity in breast, ovarian and stomach cancer cells

We used reporter gene expression analysis to characterize the effects of OA on Her-2/neu oncogene transcription. We performed transient transfection experiments with a luciferase reporter gene driven by the wild-type Her-2/neu promoter (p Nulit; Fig. 1, top panel). Exogenous supplementation with OA (20 μM; 24 h) was found to profoundly repress the activity of Her-2/neu gene promoter in SK-Br3 breast cancer cells (up to 56% inhibition; Fig. 1; bottom panel). Accordingly, a significant reduction on

Discussion

The observations reported in this study demonstrate that: (i) the PEA3 binding motif on the Her-2/neu promoter functions as a positive regulatory element for Her-2/neu gene transcription solely in cancer cells naturally exhibiting both Her-2/neu gene amplification and Her-2/neu protein overexpression (Fig. 3a); (ii) There is an inverse correlation between PEA3 and Her-2/neu expression, with low PEA3 expression occurring in Her-2/neu-overexpressing cancer cells and high PEA3 expression occurring

Conflict of interest statement

None declared.

Acknowledgments

The authors thank Prof. Mien-Chie Hung (The University of Texas M.D. Anderson Cancer Center, Department of Cancer Biology, Section of Molecular Cell Biology, Houston, Texas, USA) for kindly providing Her-2/neu promoter constructs and MCF-7/Her2-18 cells. This work was supported by the Basic, Clinical and Translational Award (BRCTR0403141) from the Susan G. Komen Breast Cancer Foundation (USA), the Breast Cancer Concept Award (BC033538) from the Department of Defense (DOD, USA) and the Special

References (48)

  • C. La Vecchia et al.

    Olive oil, other dietary fats, and the risk of breast cancer

    Cancer Causes Control

    (1995)
  • M. Stoneham et al.

    Olive oil, diet and colorectal cancer: an ecological study and a hypothesis

    J Epidemiol Community Health

    (2000)
  • C. Braga et al.

    Olive oil, other seasoning fats, and the risk of colorectal carcinoma

    Cancer

    (1998)
  • A. Tzonou et al.

    Diet and ovarian cancer: a case-control study in Greece

    Int J Cancer

    (1993)
  • A. Tzonou et al.

    Dietary factors and the risk of endometrial cancer: a case-control study in Greece

    Br J Cancer

    (1996)
  • M.A. Zamora-Ardoy et al.

    Olive oil: influence and benefits on some pathologies

    An Med Interna

    (2004)
  • J.M. Martin-Moreno

    The role of olive oil in lowering cancer risk: is the real gold or simply pinchbeck?

    J Epidemiol Community Health

    (2000)
  • T. Yamamoto et al.

    Similarity of protein encoded by the human c-erb-B-2 gene to epidermal growth factor receptor

    Nature

    (1986)
  • C.I. Bargmann et al.

    The neu oncogene encodes an epidermal growth factor receptor-related protein

    Nature

    (1986)
  • R.J. Daly

    Take your partners, please–signal diversification by the erbB family of receptor tyrosine kinases

    Growth Factors

    (1999)
  • Y. Yarden et al.

    Untangling the ErbB signalling network

    Nat Rev Mol Cell Biol

    (2001)
  • D.J. Slamon et al.

    Human breast cancer: correlation of relapse and survival with amplification of the HER-2/neu oncogene

    Science

    (1987)
  • D.J. Slamon et al.

    Studies of the HER-2/neu proto-oncogene in human breast and ovarian cancer

    Science

    (1989)
  • J.S. Ross et al.

    The HER-2/neu oncogene in breast cancer: prognostic factor, predictive factor, and target for therapy

    Stem Cells

    (1998)
  • Cited by (103)

    • Beneficial effects of olive oil and Mediterranean diet on cancer physio-pathology and incidence

      2021, Seminars in Cancer Biology
      Citation Excerpt :

      In the same line, the researchers sought to characterize the molecular mechanism by which OA down-regulates HER2 expression in BCa cells. They observed that OA increased PEA3 expression, a transcription factor, suppressing HER2 overexpression, and inhibiting HER2-dependent tumorigenesis [144]. γ-LA has raised interest as an anti-cancer agent having selective growth inhibitory effects on malignant cells in vitro.

    • Oleic acid protects against cadmium induced cardiac and hepatic tissue injury in male Wistar rats: A mechanistic study

      2020, Life Sciences
      Citation Excerpt :

      Steady consumption of olive oil reflects its diverse health benefits in humans including prevention of some cancers, risk of coronary heart diseases and also immune and inflammatory modifications [1,2] which may be due to the presence of OA [4]. Several in vivo and in vitro studies have indicated the antioxidant and anticancer properties of OA [4,5]. It has also been suggested that OA may participate in blood pressure reduction by improving endothelial function, probably by reducing reactive oxygen species (ROS) [6].

    • Extra-virgin olive oil for potential prevention of Alzheimer disease

      2019, Revue Neurologique
      Citation Excerpt :

      Over-expression of LOX-5 worsens memory and tau pathology in mice [242]. Oleic acid could have an antiproliferative effect by affecting the expression of human oncogenes; in particular it specifically represses the transcriptional activity of the Her-2/neu gene [243], analogous to the effect of Herceptin, a novel breast cancer treatment. The hydrocarbon squalene protects mammary epithelial cells against intracellular oxidative stress and DNA oxidative damage [244].

    View all citing articles on Scopus
    View full text