Fibroblast growth factors (FGF-1 or -2) are present at significant concentrations in most normal tissues in the adult. However, these FGFs are immobilized in an inactive state on the extracellular matrix and it is only poorly understood how they are solubilized and activated to reach their receptors. These growth factors can be mobilized by a previously identified secreted binding protein for FGF (BP1). We showed that the retinoid-regulated BP1 can enhance the activity of locally stored, immobilized FGFs and that expression of BP1 supports tumor growth and angiogenesis of FGF-2 positive non-tumorigenic cells. A recently identified novel BP2 showed similar biologic activities. In preliminary studies we found that addition of BP1 protein enhances FGF effects in different biological assay systems. Furthermore, expression of the BP1 cDNA was embryonically lethal in transgenic mice and caused vascular leakage in chicken embryos. BP mRNA was below detection in normal adult human or murine tissues but was detectable in murine embryonic gut and skin. Carcinogen treatment upregulates BP1 in adult mouse skin and in carcinogen-treated human skin xenografts in SCID mice. BP1 was expressed in squamous cell cancer (SCC) patient samples and cell lines as well as in colon cancer cell lines and tumor samples. In contrast, BP2 appears to be upregulated only in melanoma and was not detected in the tumor types expressing BP1. Inhibition of tumor growth was observed in human ME-180 (SCC) and Ls174T (colon cancer) cell lines in which the endogenous BP1 levels had been reduced with BP1-targeted ribozymes. This finding in conjunction with the expression of BP1 in human cancer samples suggests a rate-limiting role of BP1 for the malignant phenotype of SCC and colon cancer. We plan the following studies:
Under aim 1 we propose a series of experiments to map the BP / FGF protein / protein interactions to define these interactions at the atomic level.
Under aim 2 we will define the effects of BPs and interaction with heparansulfate on the effects induced by FGFs in cells and tissues.
Under aim 3 we will use ribozyme-targeting of BP mRNA to assess to what extent expression of the BP2 is rate limiting for the tumorigenic phenotype of melanoma and to what stage of tumor growth and metastasis BP2 and BP1 contribute most significantly.
Under aim 4 we will study the effect on BP1 expression in transgenic mice and chicken embryos. Tissue-selective vectors and conditional tetracycline-dependent expression will be used to circumvent embryonic lethality of BP1 expression.
Showing the most recent 10 out of 39 publications
