Professor
(Simon Fraser University)
AHFMR Senior Scholar

Phone: 780-492-0710
Fax: 780-492-0450
Email: zhixiang.wang@ualberta.ca

Cell Sigalling, Receptor Endocytosis, and Human Cancer

Epidermal growth factor (EGF) receptor (EGFR) and other receptor tyrosine kinases (RTKs) lie at the head of a complex signal transduction cascade that modulates cell proliferation, survival, adhesion, migration and differentiation. While EGFR signalling is essential for many normal cell functions, the aberrant activity of EGFR has been shown to play a key role in the development of cancers. EGFR receptor is overexpressed in many cancers especially in breast cancer, ovarian cancer, small cell lung cancer and skin cancer. EGFR overexpression correlates to poor prognosis, drug resistance, cancer metastasis and lower survival rate. All these make EGFR the top choice as a target for developing cancer therapies. To date, monoclonal antibodies (mAbs) and synthetic inhibitors of tyrosine kinase have taken central stage.

1. Regulation of EGFR-mediated cell signaling by the location, timing and intensity of its activation
In the past several decades tremendous progress has been made in elucidating the signaling pathways and in connecting these signaling pathway to signaling networks downstream RTKs. However, the task for the understanding of RTK-mediated cell signaling is far from finished and is significantly complicated by the recent findings that the location, timing and strength of RTK activation play critical role in regulating the signaling network and determining the physiological outcomes. Now, the regulation of RTK-mediated cell signaling by the location, timing and strength of its activation has become a major focusing of the field. We have been using EGFR as a model system to understand how the location, timing and intensity of EGFR activation regulate EGFR-mediated cell signaling. Our overall hypothesis is that the location, timing and strength of EGFR activation regulate EGF-induced cell signaling.

2. Regulation of EGF Receptor Endocytosis
The regulation of EGFR endocytosis has been an intensive research area; however, the results have been very controversial. Given that ligand binding is essential for the rapid internalization of EGFR, the events resulted from ligand binding likely contribute to the regulation of ligand-induced EGFR internalization. The immediate events following ligand binding include receptor dimerization, kinase activation, and binding to down-stream signalling and endocytic proteins. However, in spite of intense efforts, results regarding the roles of these events in EGFR internalization remain very controversial. We recently showed that inhibition of EGFR kinase activity did not block EGF-induced internalization of EGFR. Instead, EGF-induced EGFR internalization is controlled by receptor dimerization. It is possible that EGFR dimerization causes the necessary conformational changes of the receptor to expose cryptic internalization codes. Alternatively, downstream proteins essential for EGFR internalization may have a dimeric nature and can only bind to a pair of internalization codes in the dimerized EGFR. We will focus our study to reveal the molecular mechanisms by which EGF-induced EGFR dimerization controls EGFR internalization. 

3. Regulation of Growth Factor-induced Cell Signaling by Phospholipase c-1

The stimulatory effects of RTKs on cell growth are mediated by downstream signaling proteins. Phospholipace C-1 (PLC-1) is one of these signaling proteins and plays a significant role in the intracellular signaling mechanism utilized by GFs. Overexpression and hyperactivation of PLC-1 have been implicated in breast and prostate cancers. Especially, PLC-1 activity has been linked to cancer cell invasion. Recent results from our lab and the other labs suggest that PLC-1 play a much more broad and complicated role in cell signaling than previously thought. This is in part due to the mult-domain nature of PLC-1. However, the roles of PLC-1 in various GF-induced cell signaling are still very controversial. We recently Showed that PLC-1 SH3 domain interacts directly with Akt in response to EGF, which suggests a possible role of PLC-1 in EGF-induced cell survival. We also showeed that PLC-1 interacts with Rac1 to regulate cell migration. We will further study the role of PLC-1 GF-induced cell signaling and function.

Selected Publications

Pennock, S. And Wang, Z. (2008) A Tale of Two Cbls: Interplay of c-Cbl and Cbl-b in Epidermal Growth Factor Receptor Downregulation. Mol. Cell. Biol. 28: 3020-3037.

Wang, Q., Wu, F., and Wang, Z. (2007) Identification of EGF Receptor C-terminal Sequences 1005-1017 and Di-leucine Motif 1010LL1011 as Essential in EGF Receptor Endocytosis. Exp. Cell Res. 313: 3349-3363.

Wang, Y., Wu, J. and Wang, Z. (2006) Akt binds to and phosphorylates phospholipase C-gamma1 in response to epidermal growth factor. Mol. Cell. Biol. 17: 2267-2277.

Wang, Q., Villeneuve, G., and Wang, Z. (2005) Control of epidermal growth factor receptor endocytosis by receptor dimerization, rather than receptor kinase activation. EMBO Rep., 6: 942-948

Wang, Y., Pennock, S., Chen, X., Kazlauskas, A. and Wang, Z. (2004) PDGF receptor-mediated signal transduction from endosomes. J. Biol. Chem., 279: 8038-8046

Pennock, S. and Wang, Z. (2003) Stimulation of cell proliferation by endosomal epidermal growth factor receptor as revealed through two distinct phases of signaling. Mol. Cell. Biol. 23: 5803-5815

Wang, Y. and Wang, Z. (2003) Regulation of EGF-induced phospholipase C-g1 translocation and activation by its SH2 and PH domains. Traffic 4: 618-630

Wang Y, Pennock S, Chen X. and Wang Z.. Internalization of inactive EGF receptor into endosomes and the subsequent activation of endosome-associated EGF receptors. Sci. STKE 2002(161): PL17.

Wang, Y., Pennock, S, Chen, X. and Wang, Z. (2002) Endosomal signaling of epidermal growth factor receptor stimulates signal transduction pathways leading to cell survival. Mol. Cell. Biol. 22 (20): 7279-7290 [Cover illustration on MCB 22 (22)]. Science's STKE highlighted this paper in "This Week in Signal Transduction" for the October 1 issue.

Wang, Z. and Moran, M. (2002) Phospholipase C-g1: a Phospholipase and Guanine Nucleotide Exchange Factor. Molecular Intervention 2: 352-355

Chen, X. and Wang, Z. (2001) Regulation of epidermal growth factor receptor endocytosis by wortmannin through activation of Rab5 rather than inhibition of phosphatidylinositol 3-kinase. EMBO Reports 2: 842-849.

Dankort, D., Maslikowski, B., Warner, N., Kanno N. Kim, H., Wang, Z., Moran, M.F., Oshima, R.G., Cardiff, R. D. and Muller, W. (2001) Grb2 and Shc adapter proteins play distinct roles in Neu (ErbB-2)-induced mammary tumorigenesis: Implications for human breast cancer. Mol. Cell. Biol. 21: 1540-1551.

Chen, X. and Wang, Z. (2001) Regulation of EGF receptor intracellular trafficking by Rab5 in the absence of Phosphatidylinosito 3-kinase activity. EMBO Reports 2:68-74. (Cover Illustration)

Chen, X., Yeung, K. T. and Wang, Z. (2000) Enhanced drug resistance in cells coexpressing ErbB2 with EGFR or ErbB3. Biochem. Biophys. Res. Commun. 277: 757-763.

Wang, Z., Zhang, L., Yeung, K. T. and Chen, X (1999) Endocytosis deficiency of EGF receptor-ErbB2 heterodimers in response to EGF stimulation. Mol. Biol. Cell 10: 1621-1636.

Yeung, K.T., Germond, C., Chen, X. and Wang, Z. (1999) Mode of action of Taxol: apoptosis at low concentration and necrosis at high concentration. Biochem. Biophys. Res. Commun. 263: 398-404.

Wang, Z., Gluck, S., Zhang, L. and Moran, F. (1998) Requirement for PLC-gamma1 enzymatic activity in growth factor-induced mitogenesis. Mol. Cell. Biol. 18 (1), 590-597.

Dankort, D.L., Wang, Z., Blackmore, V., Moran, M. and Muller, W.J. (1997) Distinct tryrosine autophosphorylation sites negatively and positively modulate Neu-mediated transformation. Mol. Cell. Biol. 17, 5410-5425

Fam, N.P., Fan, W.-T., Wang, Z., Zhang, L.-J., Chen, H. and Moran, M. (1997) Cloning and characterization of Ras-GRF2, a novel guanine nucleotide exchange factor for Ras. Mol. Cell. Biol. 17, 1396-1406.

Wang, Z. and Moran, M. (1996) Requirement for the adaptoer protein Grb2 in EGF receptor endocytosis. Science 272, 1935-1938.

Wang, Z., Tung, P. S. and Moran, M. (1996) Association of P120 ras GAP with endocytic components and co-localization with EGF receptor in response to EGF stimulation. Cell Growth & Differentiation 7, 123-133.

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Technician

Xinmei Chen