The primary goal of our research is to understand growth factors/receptors function in vascular development and oncogenesis. Our emphasis is on Wnt and Notch signaling pathways and on biochemical dissection of these signaling cascades.

The Wnt gene family encodes secreted factors involved in such diverse phenomena as brain, kidney, uterine, and mammary gland development. Wnt-1 was originally identified as a mammary oncogene in the mouse. Wnt signaling components, most notably APC and b-catenin, are involved in human colon, melanoma, and prostate cancers. The laboratory has utilized cellular systems to define the physiologic function of Wnt proteins and the signaling pathways which carry out these functions. Our work has established that Wnt-1 can function as a mitogen, as a branching morphogen, and to induce apoptosis. The stability and signaling activity of cytosolic b-catenin is tightly regulated by Wnt action. Our studies have demonstrated that Wnt-1 signaling leads to stabilization of cytosolic b-catenin and activation of TCF-dependent transcription in mammalian cells. Our future work is designed to examine how Wnt signaling affects the cytosolic (signaling) form of b-catenin and the proteins that comprise the signaling complex.

The int-3 gene was originally identified based on its oncogenic effects in the mouse mammary gland. We have cloned the full length int-3 gene and showed that it encodes a cell surface receptor similar to Notch/lin-12 proteins, which we named Notch4. Notch4 is normally expressed in embryonic and adult endothelium. We have recently established that Notch signaling can regulate the angiogenic process. Notch4/int-3 and Jagged-1 (a Notch ligand) were able to induce cultured endothelial cells to form cellular structures with morphological and biochemical properties of endothelial microvessels. These culture systems are being used to compare and contrast the affects of Jagged/Notch with those of previously identified angiogenic factors, such as FGF or VEGF. To study Notch function in whole animals we generated animal models where Notch receptors have been activated in vasculature of mice. Using an ES-cell "knock-in", we replaced an endothelially expressed gene (Flk-1) with Notch4/int-3. The net result is expression of an activated Notch receptor in embryonic endothelium. Mice derived from these ES cells die early in embryonic development (day 7-9) and display severely impaired vascular development. The nature of the vascular defects induced by Notch signal activation is under investigation.

Selected Publications

*Parkin, N.T., Kitajewski, J., and Varmus, H.E.. Activity of Wnt-1 as a transmembrane protein. Genes. Dev. 7: 2181-93 (1993).

* Uyttendaele, H., Marazzi, G., Wu, G., Yan, Q., Sassoon, D., and Kitajewski, J. Notch4/int-3, a mammary proto-oncogene, is an endothelial cell-specific Notch gene. Development. 122: 2251-59 (1996).

* Lin, K., Wang, S., Julius, M. A., Kitajewski, J., Moos Jr., M., andLuyten, F.P. The cysteine-rich frizzled domain of Frzb-1 is required and sufficient for modulation of Wnt signaling. Proc. Natl. Acad. Sci. USA. 94: 11196-200 (1997).

* Hubbard, E.J.A., Wu, G., Kitajewski, J., and Greenwald, I. sel-10, a negative regulator of lin-12 activity in C. elegans, encodes a member of the CDC4 family of proteins. Genes Dev. 11: 3182-93 (1997).

* Shimizu, H., Julius, M. A., Giarre, M., Zheng, Z., Brown, A.M.C., and Kitajewski, J. Transformation by Wnt Family Proteins Correlates with Regulation of b-Catenin. Cell Growth Differ. 8: 1349-58 (1997).

* Uyttendaele, H., Soriano, J., Montesano, R., and Kitajewski, J. Notch and Wnt proteins function to regulate branching morphogenesis of mammary epithelial cells in opposing fashion. Dev. Biol. 196: 204-217 (1998).

* Young, C., Kitamura, M., Hardy, S., and Kitajewski, J. Wnt-1 induces growth, cytosolic b-catenin, and Tcf/Lef transcriptional activation in Rat-1 fibroblasts. Mol. Cell. Biol. 18: 2474-85 (1998).

* Julius, M.A., Rai, S., and Kitajewski, J. Chimeric Wnt proteins define the amino-terminus of Wnt-1 as a transformation-specific determinant. Oncogene. 17 (in press, 1998).