Emmanuelle Meuillet

Assistant Professor of Nutritional Sciences and Molecular & Cellular Biology
Ph.D., University Louis Pasteur, France, 1995

My research interests are focused on the regulation of the tumor suppressor, PTEN, and the survival pathway (PtdIns-3-Kinase/Akt/PTEN) and its importance in cancer and diabetes.

Research Interests

Dr. Meuillet's laboratory research interests lie in the general area of modulation of the activity of tyrosine kinases. Over the past eight years, Dr. Meuillet's work has specifically focused on understanding the molecular mechanisms and biological roles of membrane components such as phospholipids and glycosphingolipids, in receptor signaling pathways and how changes in lipid composition can affect downstream transduction signals from the plasma membrane to the nucleus. The recent discovery of lipid rafts and caveolae membrane domains has proven to be important in lipid associated disorders.

1. Studies in which membrane lipid composition has been modified have shown that lipids can modulate, for example, insulin receptor signaling. The tyrosine kinase activity of the receptor can be modulated by the lipid environment of the receptor, both in vitro (reconstitution experiments) and in intact cells (lipid-treated cell lines). For instance, membrane perturbations modify insulin biological effects to different extents and understanding how the lipid environment modulates insulin receptor signaling will increase our knowledge of diabetes, one aspect of which is lipid metabolism disorders. Insulin receptors and insulin signaling pathways are affected by lipid environment in HepG2, a human hepatoma cell line (Meuillet et al., Biochim. Biophys. Acta, 1454, (1999), p.38-48).

Lipids added in the culture medium are incorporated in different classes of phospholipids, cholesteryl esters and triglycerides. The incorporation of lipids such as linoleic acid (18:2, n-6); eicosapentaenoic acid (20:5, n-3) and cholesterol hemisuccinate, a cholesterol derivative modified insulin receptor activity and insulin signaling pathway at several levels: auto-phosphorylation of the receptor, phosphorylation of endogenous substrates, as well as metabolic effects such as glycogen synthesis and lipogenesis. Modulation of epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) receptors by another class of membrane lipid (glycosphingolipids or gangliosides) in cultured rat retina Muller glial cells has also been demonstrated (Meuillet et al., Glia, 17, (1996), p.206-216).

This is confirming the importance of lipids, in general, as modulators of phosphorylation or dephosphorylation kinetics in the action of growth factors. These changes are most probably of great biological significance since growth factors and their receptors are involved in cell growth, differentiation, migration, and invasion and cell death. It is of great interest that n-3 (or w-3) PUFA (poly-unsaturated fatty acids, abundant in fish oil) may inhibit growth and metastasis of experimental breast tumors, and (when included in the diet) may protect against breast cancer in humans. And on the contrary, n-6 PUFA can promote experimental breast cancer.

To study the effects of ganglioside, GM3 on the regulation of EGF receptor, several novel approaches were used: The first approach consisted in the stable transfection of a gene encoding an enzyme involved in the metabolism of GM3 and other gangliosides, i.e. sialidase (Meuillet et al., Cancer res., 59 (1999), p.234-240). Sialidase induced a decrease in GM3 levels in A431 epidermoid carcinoma cells and this decrease was correlated with an increase in cell proliferation and EGFR activity.

The second approach was the use of a ceramide analog, D-threo-1-phenyl-2-decannoylamino-3-morpholino-1-propanol ([D]-PDMP) which inhibits UDP-Glc:ceramide glucosyltransferase. Added to the cells, the drug induced a large depletion in glycosphingolipids and reduced the synthesis of all GSLs derived from GlcCer in A431 cells. The major ganglioside in A431 cells, GM3, was dramatically decreased in drug-treated cells and EGFR activity was increased. The addition of exogenous GM3 in drug-treated cells demonstrated the specificity of the action of the ganglioside on EGFR activity (Meuillet et al., Exp. Cell Res., 256(1):74-82, 2000).

Finally, a third approach consisted in the study of the direct interaction of EGFR with GM3 (Miljian et al., J. Biol. Chem., 277:10108-10113, 2002).

Recombinant wild type and mutated extracellular domains of the EGFR and tested them for their interaction with gangliosides GM3 and GM1. By deleting 10 aminoacids in the sub-region IV of the extracellular domain of EGFR, we abolished the binding site for GM3 specifically. Other point mutations will allow us to define more precisely the binding site for GM3 to the extracellular domain of the receptor. Using structure-activity relationships and molecular modeling studies, we are hoping to determine the GM3 interaction site with the receptor (ongoing collaboration with Dr. E. Bremer, Northwestern University, Chicago, IL).

The last approach to understand GM3-EGFR interaction was to analyze the biological significance of such an interaction in the cell (Meuillet et al., to Histochem. Cell Biol. Submitted). The idea that the addition of GM3 into the culture medium of a cell, is inducing profound modifications of the membrane signaling pathways led us to study the interaction of GM3 and EGFR in specific and highly specialized membrane domains, such as caveolae or detergent insoluble microdomains (DIG). The addition of exogenous GM3 into the culture medium of the cell is inducing a disruption of EGFR signaling in specific microdomains of the plasma membrane (Meuillet et al., in preparation). These results strongly suggest the importance of membrane domains and scaffolding proteins and the regulation of these highly organized structures in the plasma membrane by lipids.

2. At the Arizona Cancer Center, and in collaboration with Dr. Powis, Dr. Meuillet has developed a novel Akt inhibitor which structure is based on its similarity with the substrate for PdtIns-3-Kinase, i.e. phosphatidyl-myo-inositol-phosphate. In collaboration with Dr. Kozikowski (Georgetown University Medical Center, DC), D-3-Deoxy-phosphatidyl-myoinositol analogues such as the D-3-Deoxy-phosphatidyl-myoinositol (3-DPI) and the D-3-Deoxy-phosphatidyl-myoinositol ether lipid (3-DPIEL) were synthesized and tested for their ability to bind the pleckstrin homology domain of Akt and thus inhibit the kinase activity in vitro and in vivo (Meuillet et al., Mol. Can. Ther., 2003). Other compounds that are rationally designed to bind the PH domain of Akt specifically, are currently being tested in the laboratory as part of a funded collaboration between Dr. G. Mash (Chemistry Department at the U. of. A.); Dr. Mahadevan D. (Hematology-Oncology Department at the U. of A.), Dr. Powis G. (Pathology Department, U. of A.) and Dr. Meuillet.

The discovery of the possible interaction and regulation of the PdtIns-3-Kinase/Akt/PTEN pathway by a small redox protein, thioredoxin is of great relevance in cancer research (Meuillet et al., Arch. Biochim. And Biophys., in press).

My laboratory has recently demonstrated a direct interaction between thioredoxin and the tumor suppressor, PTEN. Using recombinant protein expression as well molecular modeling, we have mapped the interaction sites between the two proteins and found that reduced thioredoxin interacts with the Cys212 of the C2 domain of PTEN. This project is extensively researched in my laboratory as it represents my primary funding source at this moment (NIH-RO1 funded for 4 years). One way to study the interaction of these proteins on a genetic level was to use small organism systems such as Drosophila. Using such a system, we have been able to show a genetic and phenotypic interaction between the tumor suppressor PTEN and the redox protein Thioredoxin-1 in collaboration with Dr. Brabant M. (Director of the Small Organism Facility Core, Arizona Cancer Center). Finally, one way to modulate the interaction between PTEN and thioredoxin exists via the regulation of the thioredoxin reductase activity, using seleno-compounds. Thus, I am also studying the importance of sodium selenite and selenomethionine in cancer prevention. This funded project is in collaboration with Dr. Mark Nelson (Department of Pathology, NIH-RO1, funded for 5 year, Co-PI). Several seleno-compounds have been shown to possess chemopreventive effects in various types of cancers, such as colon and prostate cancers. Again this project may involve in the future, the use of small organism systems such as Drosophila.

My future research plans include bridging the gap between understanding the role of lipids and exploring signal transduction pathways mainly in diabetes and cancer. I am interested in investigating how lipids, carbohydrates and kinases interact in normal and abnormal conditions as well as establishing relationships to diets, diseases and prevention. These specific interactions between protein and lipids can be studied at several levels: molecularly by investigating structurally these possible interactions, biochemical by analyzing membrane microdomains in normal and abnormal conditions and finally genetically by exploring gene expression. The investigation of selective inhibition or activation of oncogenes by lipids through the analysis of gene expression modulation by specific nutrients, or via the molecular study of the occurrence of such interactions may lead to the development of new areas in cancer chemo-prevention, diabetes treatment as well as cancer treatment.

Select Publications

Any link on the below references will take you off of the BMCB site and to an abstract of that particular paper.

Meuillet, E.J.,N. Ihle, A.F. Baker, J.M. Gard, C. Stamper, R. Williams, A. Coon, D. Mahadevan, B.L. George, L. Kirkpatrick, and G. Powis. 2004. In vivo molecular pharmacology and antitumor activity of the targeted Akt inhibitor PX-316. Oncology Research 14: 513-527.

Meuillet, E.J., D. Mahadevan, M. Berggren, A. Coon, and G. Powis. 2004. Thioredoxin-1 binds to the C2 domain of PTEN inhibiting PTEN’s lipid phosphatase activity and membrane binding: a mechanism for the functional loss of PTEN’s tumor suppressor activity. Archives of Biochemistry and Biophysics 429: 123-133.

Meuillet, E.J., M. Berggren, R. Williams, L. Qiao, A.P. Kozikowski, and G. Powis. 2003. Specific inhibition of the Akt1 pleckstrin homology domain by D-3-deoxy-phosphatidyl-myo-inositol analogues. Molecular Cancer Therapeutics 4: 389-399.

Rong, S.B., Y. Hu, I. Enyedy, G. Powis, E.J. Meuillet, X. Wu, S. Wang, and A.P. Kozikowski. 2001. Molecular modeling studies of the akt ph domain and its interaction with phosphoinositides. Journal of Medicinal Chemistry 44: 898-908.

Hu, Y., E.J. Meuillet, M. Berggren, G. Powis, and A.P. Kozikowski. 2001. 3-deoxy-3 substituted-D myo inositol imidazolyl ether lipid phosphates and carbonate as inhibitors of the phosphatidylinositol 3-kinase pathway and cancer cell growth. Bioorganic and Medicinal Chemistry Letters 11: 173-176.

Hu, Y., E.J. Meuillet, M.M. Berggren, L. Qiao, G. Powis, and A.P. Kozikowski/ 2000. Synthesis and Akt inhibitory properties of a 1D-3,4-dideoxyphosphatidylinositol ether lipid. Tetrahedron Letters 41: 7415-7418.

Hu, Y., L. Qiao, S. Wang, S. Rong, E.J. Meuillet, M. Berggren, A. Gallegos, G. Powis, and A. Kozikowski. 2000. 3-(Hydroxymethyl)-bearing phosphatidylinositol ether lipid analogues and carbonate surrogates block PI3-K, Akt, and cancer cell growth. Journal of Medicinal Chemistry 43: 3045-3051.

Meuillet, E.J., B. Mania-Farnell, D. George, and E. Bremer. 2000. Modulation of EGF receptor activity by changes in the GM3 content in a Human Epidermoid Carcinoma cell line, A431. Experimental Cell Research 256: 74-78.

Contact Information

Mailing: Emmanuelle Meuillet, Assistant Professor Department of Nutritional Sciences University of Arizona Shantz 332 P. O. Box 210036 Tucson, AZ 85721-0036 Web Site: Home Page

Telephone: 520-626-5794 (Office) 520-626-9970 (Lab) Fax: 520-621-9446 Email: emeuillet@azcc.arizona.edu

http://bmcb.biology.arizona.edu BMCB Graduate Program The University of Arizona May 2008 All contents copyright © 2008. All rights reserved.

Please e-mail any comments to:
bmcb@email.arizona.edu