The expression of syndecan-1 generally appears down-regulated in human cancers and experimental models, whereas transfectional expression of syndecan-1 in cancer cells has been shown to inhibit aspects of their malignant behavior. To clarify how reduced levels of syndecan-1 may confer enhanced invasiveness, we transfected human ovarian cancer cell line HRA with antisense (AS) syndecan-1 oligodeoxynucleotide (ODN) and compared the properties of transfected cells to those of parental cells or sense (S) syndecan-1 cells. Here, we show: 1) there was lower proliferation in the AS syndecan-1 cells compared to controls (parental HRA cells and S syndecan-1 cells) when cells were incubated with HB-GFs (HB-EGF, HGF, or FGF2); 2) transfection of HRA cells with a syndecan-1 AS ODN enhanced the increase in HB-GF-dependent invasiveness; 3) in contrast, IGF-I stimulated cell proliferation and invasion, irrespective of whether cells were transfected with the AS syndecan-1 gene; 4) IGF-I stimulated ERK1/2 activation and uPA expression in both the control and AS cells, whereas the net effect of the reduction of syndecan-1 is to shift the HB-GF dose-response curve to the right; 5) the AS cells reduced activation and up-regulation of ERK1/2 phosphorylation and uPA expression, respectively, in response to HB-GFs; and 6) in comparison with early stage ovarian cancer tissues, there was a 3-fold decrease in syndecan-1 mRNA levels in advanced stage tissues. Taken together, these data suggest that decreased syndecan-1 expression may be associated with enhanced cell invasion possibly through the uPA-independent mechanism.

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