Department of Physiology and Biophysics

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Tyrosine kinases play a central role in regulating cell growth and differentiation. The mitogenic action of many polypeptide growth factors is mediated by transmembrane receptors with inducible tyrosine kinase activity. Although transient activation of tyrosine kinases is a necessary event in growth factor-induced mitogenesis, constitutive activation of the enzymes may play a pivotal role in the development and progression of cancer. For example, Src is a tyrosine kinase that is involved in signal transduction events that control normal cell growth, and is not oncogenic. Activated forms of Src, however, have been linked to a variety of human cancers: the activity of Src is increased in a large proportion of primary human breast tumors as well as in approximately 80% of colon cancers. Similarly, some forms of human chronic myelogenous leukemia (CML) and acute lymphocytic leukemia (ALL) are characterized by a chromosomal translocation that leads to deregulation of the Abl tyrosine kinase.

Oncogenic tyrosine kinases are thought to induce malignant growth by modulating the activity of cytoplasmic and plasma membrane proteins. The major research goals of our laboratory are: (1) to understand how tyrosine kinases recognize their target proteins in cells; (2) to determine how these enzymes are regulated in normal cells; and (3) to develop strategies to block the action of oncogenic tyrosine kinases. Work in the laboratory is focused on nonreceptor tyrosine kinases (Src, Hck, and Abl), as well as on the tyrosine kinase domains of the human Neu, insulin, and IGF-I receptors. For the IGF-I and insulin receptor kinases, a long-range goal is to provide a molecular explanation for the distinct biological activities of the two hormones by comparing the specificities of their respective receptors.

In addition to their tyrosine kinase catalytic domains (green), Src family kinases possess amino-terminal regulatory regions termed SH3 domains (blue) and SH2 domains (orange). These modular domains mediate intramolecular and intermolecular interactions that are important in signal transduction.

For Src-family tyrosine kinases, both of these domains are important in maintaining an inactive conformation (see structure, right. Click the image for a larger version).

The structure of the Src-family tyrosine kinase Hck, solved by Dr. John Kuriyan and his colleagues at Rockefeller University (Nature 385, 602-609). In collaboration with Dr. Kuriyan's group, we showed that displacement of the SH3 domain causes a potent activation of the enzyme (Nature 385, 650-653).

Two of the ongoing projects in the laboratory investigate the roles of SH2 and SH3 domains in signal transduction by Src-family kinases:

1. Activation of Src-family tyrosine kinases. We recently showed that the SH3 domains of Src family kinases have a major regulatory role in controlling tyrosine kinase activity. For example, binding of the HIV-1 protein Nef to the SH3 domain of the Src-family kinase Hck activates the enzyme:

For more details, see: I. Moarefi, M. LaFevre-Bernt, F. Sicheri, M. Huse, C.-H. Lee, J. Kuriyan, and W.T. Miller (1997). Activation of the Src-Family Tyrosine Kinase Hck by SH3 Domain Displacement. Nature 385, 650-653.

2. SH2 and SH3 domains assist tyrosine kinases in recognizing cellular substrates. We are investigating processive phosphorylation, a mechanism in which the SH2 domains bind to potential substrates and promote phosphorylation by the catalytic domain:

For more details on this work, see: P. Pellicena, K.R. Stowell, and W.T. Miller (1998). Enhanced Phosphorylation of Src-family Kinase Substrates Containing SH2 Domain Binding Sites. J. Biol. Chem. 273, 15325-15328.

Publications, 1994-1999

Publications, 2000