Heparan Sulfate Proteoglycans of Ras‐Transformed 3T3 or Neuroblastoma Cells

Abstract

Initial studies described the significance of heparan sulfate proteoglycans of Balb/c 3T3 cells in their adhesion on fibronectin matrices, including their binding to multiple domains in FN, the importance of this binding in microfilament and close contact formation, and the cooperativity of both HS-PG and 140k glycoprotein integrin's binding to FN to achieve tight-focal contacts under cells. These analyses utilized model HS-binding proteins, such as platelet factor 4, and proteolytic fragments of FN with differing binding activities in both cell biological analyses of adhesion responses and in biochemical analyses of the HS-PG in the adhesion sites. In contrast, dermatan sulfate proteoglycans (DS-PG) inhibit 3T3 adhesion on FN but not on collagen; of special note is the discovery that certain integrin-binding fragments of FN also contain a third HS/DS-binding domain that is cryptic and that provides a more effective mechanism for inhibiting integrin: FN binding. Kirsten Ras oncogene-transformed 3T3 cells and their nude-mouse-derived primary or lung metastatic tumors are also being analyzed by similar approaches. HS-PGs in the adhesion sites of these tumor populations undergo extensive catabolism, resulting in alteration of their binding to FN affinity columns (and by implication alteration in adhesion responses of these tumor cells on FN matrices). Functions for HS-PG on the surface of neuronal cell derivatives, e.g., neuroblastoma cells derived from the neural crest of the embryo and potentially related in some ways to peripheral neurons, are also being explored. HS-binding fragments of FN or PF4 facilitate attachment and spreading of neuroblastoma cells but not neurite outgrowth, contrasting with the ability of dorsal root ganglion neurons to extend neurites on HS-binding substrata. The catabolism of HS-PG in neuroblastoma adhesion sites is minimal, indicating that this cannot be the explanation for incompetence in neurite extension. Neurite extension by neuroblastoma cells on FN results from three different and overlapping binding activities of non-PG receptors on the cell surface--RGDS-dependent binding to integrin, an RGDS-independent mechanism (perhaps a cell type-specific domain), and a ganglioside-dependent process. However, these neurite-extending reactions can be modulated either by exogenous addition of proteoglycans acting in a "trans" manner with the cell surface or by endogenous HG-PG acting in a "cis" manner with one or more of these receptors.(ABSTRACT TRUNCATED AT 400 WORDS)