Differential expression of fibronectin and its degradation products in malignant tumors

This chapter discusses the differential expression of specific fibronectins (FNs) mRNA isoforms in association with malignant tumors, either in in vivo or in in vitro systems. FNs are high-molecular-weight multifunctional glycoproteins present in the extracellular matrices (ECM) of connective tissues playing a crucial role in cell adhesion, spreading, and migration. In conjunction with the loss of FN, transformed cells lose other ECM components, procollagens, laminin, and heparan sulfate as well as hyaluronic acid. FNs are particularly abundant in body fluids, loose connective tissue, granulation tissue, basement membranes, and in many developing tissues, but are often reduced or absent from the corresponding differentiated tissues. Since FN is maintaining the normal cell phenotype, the expression of FN probably represents a host reaction antagonizing tumor growth and invasion. The activation of proteolysis and the generation of FN degradation products with associated transformation enhancing factor activity may represent a relevant step in tumor growth and progression.