The overall goal of the proposed research is to understand how changes in specific adhesive molecules contribute to the invasive or metastatic capacity of tumor cells. The studies focus primarily on the neural cell adhesion molecule N-CAM because transformation of neuroepithelial cells by Rous sarcoma virus (RSV) results in a dramatic reduction in amount of N-CAM and associated cell adhesiveness together with an increase in cell motility. The studies employ biochemical and functional assays that are based on specific antibodies to defined CAMs, and make use of cloned sequences to analyze the genetic regulation of their expression. To determine how changes in N-CAM expression affect the malignant behavior of cell, the adhesion, motility and invasiveness of fully transformed cells that have lost N-CAM will be compared to that of transformed cells in which N-CAM levels have been restored by genetic manipulation. To determine how N-CAM levels are reduced, we will measure the transcription, processing, and stability of N-CAM mRNA and the phosphorylation and stability of N-CAM protein, and will define control regions in the N-CAM gene that are necessary for the RSV-induced change. The effect of transformation on the expression of other defined neuronal adhesion systems will also be determined. To identify factors that may directly enhance tumor cell invasiveness, we will test whether transformed cells secrete substances that specifically alter the synthesis and degradation of CAMs on normal surrounding cells. In addition, the effect of transformation on expression of CAMs will be assessed in epithelial cells that give rise to carcinomas. The loss of a major cell adhesion system may be a prime contributor to tumor cell detachment and local invasiveness. The proposed studies will test this idea and will define mechanisms that alter adhesiveness in tumor cells. The findings may suggest new approaches for clinical intervention in the metastatic spread of human tumors.
