Kunxin Luo Staff Scientist, LBNL KLuo@lbl.gov Mailstop: Donner & Adjunct Assistant Professor University of California, Berkeley Dept. of Molecular & Cell Biology

The TGFß family of cytokines play important roles in tumor suppression, cell differentiation and extracellular matrix production. We are interested in the signal transduction pathways downstream of the transforming growth factor ß (TGFß) receptors and the role of these pathways play in regulation of mammary epithelial cell differentiation and breast carcinogenesis. We wish to understand how TGFß induces a wide range of biological functions and identify components of the TGFß receptor signaling pathways. Current model of TGFß signaling: Binding of TGFß to the cell surface receptors results in activation of receptor kinases, which phosphorylate and activate downstream Smad2 and Smad3 proteins. Phosphorylated Smad2 and Smad3 then form heteromeric complexes with Smad4 and translocate to the nucleus where they activate transcription of multiple TGFß response genes. An important question we are interested in addressing is how this simple pathway is able to mediate a wide variety of TGFß-induced signals and what role this pathway plays in mammary gland development and breast cancer. Our current research is designed to address the following questions: How does Smad proteins activate a wide range of TGFß-induced biological functions? Our working hypothesis is that Smad proteins activate multiple TGFß-induced signaling activities by interacting with different cellular partners. Our goal is, then, to identify these cellular partners and investigate these molecules regulate Smads function. Using biochemical approaches, we have identify several molecules interacting with different Smad proteins. Interestingly, two of the molecules we identified are oncogene products. These oncoproteins, when overexpressed, can induce transformation of cells. An interesting question now is how interaction between oncoproteins and tumor suppressors (Smad proteins) regulates cell growth and carcinogenesis. Studies are being carried out to address this question. We are also investigating the function of other Smad-interacting proteins we have identified. What is the role of TGFß signaling pathway in mammary epithelial cell differentiation and breast cancer? In vitro studies using tissue culture cell lines allow us to carry out biochemical studies to understand the function and regulation of individual signaling molecules. Once this goal is achieved, we wish to apply these knowledge to an in vivo system and try to understand the role of the signaling pathway in a complex biological process. For this, we will use mammary epithelial cell differentiation and breast cancer as a model system. By introducing dominant negative and constitutive active mutants of TGFß signaling molecules, we will attempt to address the importance of TGFß signaling in different stages of mammary epithelial cell differentiation and how deregulation of TGFß signaling contributes to breast cancer. Selected Publications: Luo, K., Zhou, P., and Lodish, H. F. (1995) The specificity of the TGF-ß receptor kinases determined by a novel addressable peptide library. Proc. Natl. Acad. Sci., 92, 11761-11765. Luo, K. and Lodish, H. F. (1996) Signaling by chimeric erythropoietin-TGF ß receptors: Homo- dimerization of the Cytoplasmic Domain of the Type I TGF-ß Receptor and Hetero-dimerization with the Type II Receptor are both Required for Intracellular Signal transduction. EMBO J., 15, 4485-4496. Luo, K. and Lodish, H. F. (1997) Positive and negative regulation of type II TGFß receptor signal transduction by autophosphorylation on multiple serine residues. EMBO J., 16, 1970-1981. Zhou, Q., Chen, D., Pierstorff E., and Luo K. (1998) Transcription elongation factor P-TEFb mediates Tat activation of HIV-1 transcription at multiple stages. EMBO J. 17, 3681-3691. Stroschein, S. L., Wang, W., and Luo, K. (1999) Cooperative binding of Smad proteins to two adjacent DNA elements in the plasminogen activator inhibitor-1 promoter mediates TGFß-induced, Smad-dependent transcriptional activation. J. Biol. Chem. 274, 9431-9441. Luo, K., Stroschein, S. L., Wang, W., Chen, D., Martens, E., Zhou, S. and Zhou, Q. (1999) Ski interacts with the Smad proteins to repress TGFß signaling. Submitted.