W. (Todd) Todd Miller, Ph.D. (Professor)

Tyrosine kinases play a central role in regulating cell growth and differentiation. 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.

One goal of our studies is to understand how the noncatalytic SH2 and SH3 domains of nonreceptor tyrosine kinases influence enzymatic activity. For Src-family tyrosine kinases, both of these domains appear to be important in maintaining an inactive conformation (see structure above). For the Src-family kinase Hck, we showed that binding of the HIV-1 protein Nef, a high-affinity ligand for the SH3 domain, causes a potent activation of the enzyme. This suggests that other cellular proteins that bind the SH3 domains of Src-kinases may regulate tyrosine kinase activity. We are also investigating how the SH2 and SH3 domains of nonreceptor tyrosine kinases are involved in recognition of protein substrates.