The long-term objective of this application is to understand the mechanisms by which carcinoma cells in situ undergo a conversion that allows them to invade and metastasize.
The specific aims of this project are to investigate the role of growth factors and their cognate receptors in such conversion. The rat bladder carcinoma cell line NBT-II offers the unique opportunity to study the role of dual function growth/scatter factors in inducing the conversion from an epithelial to a migratory fibroblastic state in sparse cultures while these same factors are strictly mitogenic in confluent cultures. NBT-II cells expressing growth/scatter factors invade bladders in organ cultures and form large primary tumors and metastases without delay in nude mice. A novel scatter factor produced by a NBT-II fibroblastic clone derived from a lymph node metastasis will be isolated and sequenced, and its mode of action will be studied during tumor progression. An important issue is to determine whether subpopulations of tumor cells expressing growth factors will have proliferative, invasive, and metastatic advantage over the other cells of the tumor or behave as helper cells within the tumor. Tumors containing known proportions of untransfected NBT-II cells and NBT-II cells expressing growth factors and overexpressing or lacking their receptors will be followed to define cross-signalling mechanisms between subpopulations in primary tumors. chemically-induced bladder tumors will be produced in mice and screened by PCR for the production of growth/scatter factors and their receptors at specific stages of tumor progression. Cell lines derived at different stages will be characterized for their invasive and metastatic properties determined in in vitro orthopic assays and in vivo. To demonstrate the role of a particular growth factor or its receptor at a given stage during tumor progression cell lines derived from tumors of lower grades will be transfected to express the factor or its receptor while cell lines of higher grades will be transfected with appropriate cDNA probes to suppress their expression. PCR-based screening of growth factors and their receptors will be applied to human bladder carcinoma of different grades. The identification of specific growth factors and/or their receptors involved in the transition from in situ carcinoma of bladder to invasive and metastatic phases will help in designing transgenic mice where their expression will be targeted to the urothelium. TGFalpha transgenic mice will be used as a model for the study of the role of growth factors in the formation and progression of chemically-induced tumors. This project should allow us to establish a clear-cut correlation between the expression of growth/scatter factors and the acquisition of epithelial plasticity as a mechanism for the dissemination of carcinoma.
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