The Epidermal Growth Factor Receptor (EGFR or ErbB1) is a member of the ErbB family, which comprises four members, ErbB1-4. EGFR is a tyrosine kinase that plays a fundamental role in growth and proliferation of a large variety of different cell types and the receptors of the ErbB family have been associated with different cancers. In order to develop new treatments, it is important to gain an understanding of how the receptor functions on a molecular level (for some recent reviews see Ref. -).
The EGFR is one of the best studied receptor proteins. Nevertheless, a clear understanding of how the receptor is activated and its fate after activation has been elusive. Originally it was suggested that the EGFR and ErbB family receptors exist predominantly in a monomeric form and only after ligand binding form dimers in which the receptors can autophosphorylate, leading to downstream signaling,. Further studies, though, showed pre-formed dimers that underwent a conformational change upon activation , . These studies lead to new experiments in which researchers tried to quantify which fractions of receptors are in a monomeric or dimeric form. An evidence, among others as well from our lab, indicated a large percentage of pre-formed dimers on the membrane in the absence of ligand -. Further studies by the group of Andrew Clayton even indicate that dimerization might not be enough and even higher order oligomers are the active receptor species ,.
In our lab we are trying to quantify the monomer/dimer/oligomer fractions in the absence of ligand, as well as the signaling cascade following EGFR activation in live cells or tissues. For that purpose we have determined the dimer fraction of EGFR in the absence of ligand on living cells. In addition, we have measured the dissociation constant of downstream signaling molecules, Cdc42, and several effectors in live cells  and zebrafish embryos . Our long term goal is to quantify the interactions between the different molecules of a signal transduction pathway within cells and organisms using fluorescence spectroscopy approaches.
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 Liu, P.;, Sudhaharan, T.; Koh, R.M.; Hwang, L.C.; Ahmed, S.; Maruyama, I.N.; Wohland, T. Investigation of the dimerization of proteins from the epidermal growth factor receptor family by single wavelength fluorescence cross-correlation spectroscopy. Biophysical Journal 2007 Jul 15;93(2):684-98.
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 Clayton, A.H.; Orchard, S.G.; Nice, E.C.; Posne,r R.G.; Burgess, A.W, Predominance of activated EGFR higher-order oligomers on the cell surface, Growth Factors 2008 Dec 26(6):316-24.
 Sudhaharan, T.; Liu, P.; Foo, Y.H.; Bu, W.; Lim, K.B.; Wohland, T.; Ahmed S. Determination of in vivo dissociation constant, KD, of Cdc42-effector complexes in live mammalian cells using single wavelength fluorescence cross-correlation spectroscopy, J Biol Chem, 284 (2009) 13602-13609.
 Shi, X.; Foo, Y.H.; Sudhaharan, T.; Chong, S.W.; Korzh, V.; Ahmed, S.; Wohland, T. Determination of dissociation constants in living zebrafish embryos with single wavelength fluorescence cross-correlation spectroscopy, Biophys J, 97 (2009) 678-686.