Tyrosine Kinase Signal Transduction Pathways

Many growth factors bind to cell-surface receptors that contain intrinsic tyrosine kinase activity. These receptors phosphorylate themselves and other intracellular proteins on tyrosine residues and through a poorly understood mechanism initiate cell growth and division. Uncontrolled activity of such tyrosine kinases leads to various animal and human cancers. Our group characterizes the signaling pathways utilized by tyrosine kinases to better understand cell growth, development and transformation processes.

Growth factor receptors, when tyrosine phosphorylated, bind proteins containing a 100-amino-acid motif called the SH2 domain. SH2-domain proteins are critical for many aspects of growth factor receptor signaling. We developed a method to clone additional signaling molecules with SH2 domains, wherein we label the carboxyterminus of the epidermal growth factor receptor by incubating the receptor with radioactive ATP. This allows the receptor to incorporate radioactive phosphate at its tyrosine phosphorylation sites and bind SH2-domain proteins. We use this radiolabeled receptor to screen protein-expression libraries in which protein sequences from mammalian cells are expressed in bacteria. With this method we cloned several new SH2-domain proteins. We now study the function of these new SH2-domain proteins in cell growth and in growth-factor-mediated oncogenesis.

SH2-domain proteins cloned by screening bacterial expression libraries with radioactively labeled epidermal growth factor receptor. Recent

Representative Publications:

• Margolis, B.L., Rhee, S.G., Felder, S., Lyall, R., Levitski, A., Ullrich, A., Zilberstein, A., and Schlessinger, J. (1989)
• phospholipase C-II A potential mechanism for EGF-receptor signalling. Cell 57 1102-1107. Margolis, B., Li, N., Koch, A., Mohammadi, M., Hurwitz, D., Zilberstein, A., Ullrich, A., Pawson, T., and Schlessinger, A. (1990)
• phosphorylated carboxyterminus of the EGF receptor is a binding site for GAP and PLC-[[gamma]]. EMBO J. 9 4375-4380. Skolnik, E., Margolis, B., Mohammadi, M., Lowenstein, E., Fischer, R., Dreps, A., Ullrich, A., and Schlessinger, J. (1991)
• proteins for receptor tyrosine kinases utilizing a novel expression/cloning approach. Cell 65 83-90. Margolis, B. (1992)