Enhanced Expression of Type IV Collagen‐binding Protein (p29) in Fyn‐transfected Murine Fibrosarcoma Cells

We investigated the mechanism of the enhancement of metastatic potential induced by transfection of the fyn gene, a member of the src family. We employed two murine fyn cDNA‐transfected clones, ML‐SN1 and ML‐SN2, which were previously established from an ML‐01 low‐metastatic clone of Meth A sarcoma of BALB/c mice and were proven to have higher metastatic ability than ML‐01 and the mock‐transfected clone ML‐MT‐neo (Takayama et al., 1993). Our present investigation revealed that the two transfectants showed higher metastatic ability and higher rates of adherence to type IV collagen than ML‐MT‐neo. However, no difference was found in in vitro or in vivo growth rates, attachment to laminin or endothelial cells or cell motility through a reconstituted basement membrane. Analysis of surface membrane proteins labeled with (125)I on SDS‐PAGE showed that a 29 kD band specifically bound to type IV collagen‐coupled beads was more intense in ML‐SN2 than in ML‐MT‐neo. Genistein, a protein tyrosine kinase inhibitor, dramatically reduced protein tyrosine kinase (PTK) activity of ML‐SN2 in a dose‐dependent fashion, corresponding to the reduction of adhesiveness to type IV collagen. The expression of the type IV collagen‐binding protein (p29) of ML‐SN2 was also reduced significantly by genistein treatment. These results suggested that the fyn product in Meth A cells augments the expression of a type IV collagen‐binding protein through elevation of the PTK activity of the membrane fraction and thus facilitates the metastasis of Meth A.