PLEIOTROPHIN-- AN ANGIOGENIC SWITCH IN TUMOR PROGRESSION

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The long-range goals of this research are to identify and characterize whereby pleiotrophin (PTN) and midkine (MK) signal neovascularization in tumors (i.e., "tumor angiogenesis") and to identify and exploit the sites and methods to therapeutically control pathological angiogenesis and human tumors. Both PTN and MK are highly expressed in many aggressive human tumors and cell lines from these tumors constitutively express PTN and MK, suggesting that their expression is the result of a genetically stable mutation in the transformed cell. PTN transformed cells and tumor cells in which constitutive expression of PTN or its C-terminal domain alone have been established develop highly vascular tumors in the nude mouse. Remarkably, the cells that express PTN release basic fibroblast growth factor (bFGF) to extracellular sites but non-transformed control cells do not, suggesting that bFGF release is transformation-dependent and the result of a PTN signaled pathway. Basic FGF release from transformed cells is also stipulated by PMA, suggesting that bFGF release is dependent on an activated protein kinase C (PKC) isoform. These findings may be very relevant to human tumors, since interruption of endogenous PTN signaling by a dominant negative PTN effector reverses aggressive growth of human breast cancer cells. Since there is a striking similarity of both structure and functions of PTN and MK and expression of these highly related cytokines is a feature of many aggressive and high vascularized tumors, it is mow proposed to exploit the models used to generate the Preliminary Data cited above to functionally dissect and compare the different domains of PTN and MK that lead to tumor promotion and tumor angiogenesis. The proposal seeks to define oncogenic pathways with which PTN- OR mk- "cooperates to initiate transformation and tumor promotion, to identify downstream genes and pathways which are activated by PTN or MK stimulated signaling that lead to tumor angiogenesis, to seek the factor(s) such as an activated PKC isoform or bFGF which may directly mediate PTN and MK signaled tumor angiogenesis and to define new targets in PTN and MK signaling pathways for therapies to reverse the stepwise progression of tumors in man. The results are likely to identify "angiogenic switch(s)" of potential broad importance in human tumors, advance knowledge of vasculogenesis and identify potential sites for therapeutic intervention.