Tumor cells avidly secrete various
proteinases, and cascades of proteolytic activation occur around the cells. Therefore,
cell surface receptors of
tumor cells are under the constant influence of
proteinases. In this study, the effects of
serine proteinases on
integrin-medicated cell-matrix interactions were studied in C32TG and Mewo human
melanoma cells. These
melanoma cells were pretreated with
proteinases and their adhesive properties on various substrata were evaluated by cell adhesion assays. Paradoxically, appropriate cell surface proteolysis enhanced the RGD-sensitive cell adhesion on
fibrinogen and
vitronectin, but not the RGD-insensitive adhesion on
type I collagen or
laminin. Pretreatment of these cells with 0.1 to 1 microM of
trypsin,
chymotrypsin, or
plasmin for 30 min at 37 degrees C increased the number of spread cells on
fibrinogen and
vitronectin by 200-300%. The enhancement of cell spreading was not accompanied by up-regulation of the relevant RGD-sensitive
integrin expression. Analysis of the
cell surface receptor by
GRGDSPK-
Sepharose affinity chromatography showed that
trypsin treatment did not up-regulate alpha v
beta 3 integrin, an RGD-sensitive receptor for
fibrinogen and
vitronectin in the
melanoma cells, nor the induced appearance of novel receptors. Treatment of cells with 100 nM
proteinases increased cell binding of both monoclonal and polyclonal
antibodies against alpha v
beta 3 integrin subunits by 70%, but not that of
monoclonal antibody against alpha 2, alpha 3, or alpha 6 subunit, indicating that cell surface proteolysis exposed more alpha v
beta 3 integrin on the cell surface. These results suggest that exposure of alpha v
beta 3 integrin is a part of the mechanisms underlying the
serine proteinase-induced enhancement of
melanoma cell adhesion on
fibrinogen and
vitronectin.