Department of Molecular Cell BiologyProf. Sima Lev |
 972-8-934-2126 972-8-934-4125 Sima.Lev@weizmann.ac.il Homepage |
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Normal cell growth and motility are controlled by complex signaling pathways that respond to diverse environmental cues including nutrients, growth factors, hormones and components of the extracellular matrix (ECM). Understanding how intracellular signaling networks function in normal cells, and how they are altered in cancer cells is a major challenge of cancer cell biology research. The long-term goal of our studies is to define the signaling pathways and the intracellular signaling components that contribute to the development and progression of breast cancer. In particular, we are interested in signal transduction pathways that are regulated by lipid second messengers, as well as those that are regulated by cell-matrix adhesion and affecting cell motility, invasion and cancer metastasis.
Ongoing projects focus on:
(1) Signaling pathways mediated by the non-receptor tyrosine kinase PYK2, which we originally isolated (Lev et al, 1995) and subsequently demonstrated its involvement in diverse signaling cascades triggered by ECM, growth-factors, hormones and neuropeptides (Dikic et al, 1996, Litvak et al, 2000, Tian et al, 2000). PYK2 appears to regulate the growth and motility of different cell types, and to converge signaling pathways of integrins, growth factor and G-proteins coupled receptors (Litvak et al, 2000). Its expression level is upregulated in several human tumors, and it is often associated with poor prognosis, high metastasis and reduced survival. Hence, PYK2 can be a therapeutic target for diverse human cancers. We are seeking to understand how PYK2 modulates cell growth and motility and consequently contributes to breast cancer progression and metastasis.
(2) Signaling pathways mediated by lipid second messengers. Lipid second messengers are key regulators of multiple signaling pathways that control cell survival, growth and motility. Aberrant levels of these second messengers are often found in malignant cells due to abnormal activity and/or expression of proteins and enzymes that regulate their production and/or turnover. Several oncogenes and tumor suppressor genes, such as PI3K and PTEN, respectively, directly control the levels of certain intracellular lipid species. Understanding how normal cells maintain critical levels of lipid second messengers, and how the level of these second messengers is modified in cancer cells is a major challenge of an active research field. Over the past few years, our extensive studies on the phosphatidylinositol (PI)-transfer protein Nir2 (Lev et al, 1998, 2004, Litvak et al, 2002, 2004, 2005, Tian et al, 2002), and on other lipid-transfer proteins (LTPs), suggest that these proteins regulate the level and distribution of several intracellular lipids, thereby controlling diverse cellular processes including lipid metabolism and membrane trafficking events (Litvak et al, 2005, Peretti et al, 2008, Lev. S. 2010, 2012). We recently found that Nir2 plays an important role in various growth factor receptors signaling cascades, and that it modulates the growth, motility and invasion of normal human mammary cells and different subtypes of human breast carcinomas. Our current efforts are aimed at elucidating the underlying mechanisms of Nir2 functions in cell growth, migration and invasion using molecular cell biology approaches and appropriate animal models.
(3) Signaling pathways that regulate intracellular lipid biosynthesis and homeostasis. Increased de novo lipid biosynthesis is a hallmark of proliferating cancer cells, and is frequently associated with tumor progression. Hence, the identification of cellular regulators of intracellular lipid biosynthesis could lead to the development of new strategies for cancer therapy. The integral ER-membrane protein VAP-B and its closely related VAP-A protein (Lev et al, 2008) appear to regulate intracellular lipid transport and biosynthesis. These proteins interact directly with various LTPs (Amarilio et al, 2005, Lev. S. 2010, 2012), and also with regulatory components of the de novo biosynthesis machineries of cholesterol and fatty acids, including SREBP-1 and Insig-1, thereby regulating intracellular lipid homeostasis. VAP-B is often amplified or overexpressed in metastatic human breast cancer, but its contribution to breast cancer tumorigenesis has, as yet, not been demonstrated. Our current studies are aimed at elucidating the role of VAP-B in human breast cancer development and metastasis.
 Figure 1: The non-receptor tyrosine kinase PYK2 and its downstream signaling pathways that regulate cell proliferation, migration and invasion. PYK2 contains several structural domains including, an N-terminal FERM domain that interacts with the Nir proteins (Nir1, Nir2 and Nir3), a central kinase domain, two short proline rich domains (brown) that interact with multiple SH3 containing proteins, and a C-terminal focal adhesion targeting (FAT) domain. Its major autophosphorylation site Y402 and the two tyrosine residues Y570 and Y580 in its kinase domain, which provides a binding site for Src (Y402) and are subsequently phosphorylated by Src (Y570 and Y580), respectively, are critical for its kinase activity. pY881 binds the SH2 domain of GRB2 |
 Figure 2: Nir2 and its potential roles in cell proliferation and migration. Its N-terminal PI-transfer domain could affect the levels of key phosphoinositides second messengers, and consequently their downstream signaling pathways. Its interacting proteins: VAP-A&B, which bind to its FFAT motif could influence lipid transport and biosynthesis, and PYK2, which interacts with its C-terminal domain can influence focal adhesion and MAP kinase signaling pathways. |
ISF, Minerva, ICA, BSF
Selected publications
Lev, S. (2012) Non-vesicular lipid transport from the ER. Cold Spring Harb Perspect. Biol.
Laufman O, Hong WJ, Lev S (2011) The COG complex interacts directly with Syntaxin 6 and positively regulates endosome-to-TGN retrograde transport. JOURNAL OF CELL BIOLOGY 194, 459-472 
Lev S (2010) Non-vesicular lipid transport by lipid-transfer proteins and beyond. NATURE REVIEWS MOLECULAR CELL BIOLOGY 11, 739-750
Kim S, Leal SS, Ben Halevy D, Gomes CM, Lev S (2010) Structural Requirements for VAP-B Oligomerization and Their Implication in Amyotrophic Lateral Sclerosis-associated VAP-B(P56S) Neurotoxicity. JOURNAL OF BIOLOGICAL CHEMISTRY 285, 13839-13849
Laufman O, Kedan A, Hong WJ, Lev S (2009) Direct interaction between the COG complex and the SM protein, Sly1, is required for Golgi SNARE pairing. EMBO JOURNAL 28, 2006-2017
Lev S, Ben Halevy D, Peretti D, Dahan N (2008) The VAP protein family: from cellular functions to motor neuron disease. TRENDS IN CELL BIOLOGY 18, 282-290
Peretti D, Dahan N, Shimoni E, Hirschberg K, Lev S (2008) Coordinated lipid transfer between the endoplasmic reticulum and the Golgi complex requires the VAP proteins and is essential for Golgi-mediated transport. MOLECULAR BIOLOGY OF THE CELL 19, 3871-3884
Lev S (2006) Lipid homoeostasis and Golgi secretory function. BIOCHEMICAL SOCIETY TRANSACTIONS 34, 363-366
Amarilio R, Ramachandran S, Sabanay H, Lev S(2005) Differential regulation of endoplasmic reticulum structure through VAP-Nir protein interaction. JOURNAL OF BIOLOGICAL CHEMISTRY 280, 5934-5944
Litvak V, Dahan N, Ramachandran S, Sabanay H, Lev S(2005) Maintenance of the diacylglycerol level in the Golgi apparatus by the Nir2 protein is critical for Golgi secretory function. NATURE CELL BIOLOGY 7, 225-U14
25. Litvak, V., Argov, R., Dahan, N., Ramachandran, S., Amarilio, R., Shainskaya. A, and Lev, S. (2004) Mitotic phosphorylation of the peripheral Golgi protein Nir2 by Cdk1 provides a docking mechanism for Plk1 and affects cytokinesis completion. Molecular Cell. 14, 319-330
Litvak, V., Tian, D., Carmon. S, and Lev, S. (2002) Nir2, a human homolog of the Drosophila rdgB, is essential for cytokinesis. Mol. Cell. Biol. 22, 5064-5075.
Litvak, V., Tian, D., Shaul, Y.D. and Lev, S. (2000) Targeting of PYK2 to focal adhesions as a cellular mechanism for convergence between integrins and GPCR signaling cascades. J. Biol. Chem. 275, 32736-32746.
Lev, S., Hernandez, J., Martinez, R., Chen, A., Plowman, G.D., and J. Schlessinger. (1999) Identification of a novel family of targets of PYK2 related to Drosophila Retinal Degeneration B (rdgB) protein.
Lev, S., Moreno, H., Plowman, G.D., Martinez, R., Peles, E., Canoll, P., Musacchio, J.M., Rudy, B., and J. Schlessinger. (1995) Protein tyrosine kinase PYK2 involved in Ca+2 induced regulation of ion channel and MAP kinase functions. Nature, 376, 737-745
Keywords
Lipid, trafficking, migration, invasion, focal adhesions