Robert L. Geahlen, Ph.D. Professor of Medicinal Chemistry Phone: (765) 494-1457 E-mail: geahlen@purdue.edu Full directory listing

Specialization: Biochemistry and Molecular Biology

Education

Research: Biochemistry and Molecular Biology

Signals transduced by the binding of antigens to receptors on hematopoietic cells take the form of increased tyrosine phosphorylation of intracellular proteins. Since the components of the receptor complex itself lack intrinsic enzymatic activity, these responses are mediated instead by cytoplasmic protein-tyrosine kinases that associate with the liganded receptor. The major focus of our laboratory is on understanding how these kinases are regulated and how, once activated, they regulate the multiple biochemical pathways that are activated by receptor engagement. The kinase of particular interest is Syk, a 72-kDa, cytoplasmic protein-tyrosine kinase originally discovered in our laboratory. We use chemical, biochemical and genetic approaches to understanding the role of each of these enzymes in signal transduction pathways downstream from B cell antigen receptors. Our current work is directed in several areas.

Structure-Function Analysis of Syk in Hematopoietic Cells: B cells fail to develop properly in mice lacking the gene for Syk due to the inability of pre-B cell antigen receptors to signal in the absence of the kinase. How Syk mediates signaling through B cell antigen receptors is a major question being investigated. We have mapped multiple sites of phosphorylation on Syk that are important for its ability to function in B cells. By site-directed mutagenesis and expression studies, we are exploring the role of these phosphorylations in the ability of Syk to complement signaling in Syk-deficient cells. We have also identified regions of Syk required for its translocation into and out of the nucleus. The role that Syk's nucleocytoplasmic translocation plays in modulating the properties of cells is actively under investigation.

Interactions of Syk with Intracellular Proteins: Through the use of genetic and biochemical screens, we are identifying and characterizing novel Syk-interacting proteins that may be involved both in signal transduction pathways operating downstream of activated Syk and in the subcellular localization of the kinase. In collaboration with Dr. Carol Post, we are examining the structural bases for these interactions.

Syk in Breast Epithelial Cells: In addition to hematopoietic cells, Syk also is expressed in many other cell types including mammary epithelial cells. In breast cancer cells, the expression of Syk is inversely correlated with invasiveness. We are exploring the role of Syk in regulating the growth properties of breast epithelial cells.

Inhibitors of Protein-Tyrosine Kinases: In collaboration with Dr. Richard Borch, we are developing and characterizing chemical probes that target the SH2 domains of protein-tyrosine kinases that mediate protein-protein interactions.

Representative Publications

Geahlen, R.L. (2009) Syk and pTyr'd: Signaling through the B cell antigen receptor. Biochim. Biophys. Acta 1793, 1115-1127.

Zhang, X., Shrikhande, U., Zhou, Q., and Geahlen, R.L. (2009) A role for the protein-tyrosine kinase, Syk, in regulating cell-cell adhesion and motility in breast cancer cells. Mol. Cancer Res. 7, 634-644.

Zhou, Q., and Geahlen, R.L. (2008) Interaction of the protein tyrosine kinase Syk and TRAF-interacting protein (TRIP) in the tumor necrosis factor (TNF)-mediated survival pathway in breast epithelial cells. Oncogene 28, 1348-1356.

Wang, J., Bao, N., Paris, L.L., Geahlen, R.L., and Lu, C. (2008) Total internal reflection fluorescence flow cytometry. Anal. Chem. 80, 9840-9844.

Zhang, Y., Oh, H., Burton, R.A., Burgner, J.W., Geahlen, R.L., and Post, C.B. (2008) Tyr130 phosphorylation triggers Syk release from antigen receptor by long-distance conformational uncoupling. Proc. Natl. Acad. Sci. USA 105, 11760-11765.

Wang, J., Bao, N., Paris, L.L., Wang, H.-Y., Geahlen, R.L., and Lu, C. (2008) Detection of kinase translocation using microfluidic electroporative flow cytometry. Anal. Chem. 80, 1087-1093.

Li, M, Ong, S.S., Rajwa, B., Thieu, V.T., Geahlen, R.L., and Harrison, M.L. (2008) The SH3 domain of Lck modulates TCR-dependent activation of Erk through activation of Raf-1. Mol. Cell Biol. 28, 630-641.

Oh, H., Ozkirimli E., Shah, K., Harrison, M.L., and Geahlen, R.L. (2007) Generation of an analog-sensitive Syk tyrosine kinase for the study of signaling dynamics from the B cell antigen receptor. J. Biol. Chem. 282, 33760-33768.

Garrido-Hernandez, H., Moon, K.D., Geahlen, R.L. and Borch, R.F. (2006) Design and synthesis of phosphotyrosine peptidomimetic prodrugs. J. Med. Chem. 49,3368-3376.

Zhou, F., Galan, J., Geahlen, R.L. and Tao, W.A. (2006) A novel quantitative proteomics strategy to study phosphorylation-dependent peptide-protein interactions. J. Proteome Res. 6, 133-140.