Adenovirus E1A represses protease gene expression and inhibits metastasis of human tumor cells

Stable transfection of human tumor cell lines with the adenovirus-5 E1A gene repressed the expression of the secreted proteases, type IV collagenase, interstitial collagenase and urokinase. In addition, E1A blocked the 12-O-tetradecanoyl phorbol acetate (TPA) induction of interstitial collagenase transcription in HT1080 fibrosarcoma cells. Plasmids bearing the interstitial collagenase or type IV collagenase 5′ flanking regions linked to a chloramphenicol acetyl transferase coding sequence were constructed and analysed for expression by transient cotransfections into HT1080 cells. Cotransfection with a plasmid bearing a functional E1A gene repressed transcription of the type IV collagenase promoter and blocked the TPA induction of the interstitial collagenase promoter. Furthermore, E1A repressed transcription from a TK promoter driven by AP-1 complex binding sites (TRE), suggesting that E1A interferes with the AP-1 trans-activation pathway. This effect was not, however, due to the repression of c-jun gene transcription by E1A. In fact, the expression of E1A rendered the c-jun gene hypersensitive to TPA induction. Concomitant with reduction in expression levels of secreted proteases, stable E1A transfectants showed reduced metastatic activity in vivo and reduced ability to traverse a reconstituted basement membrane in vitro. Monospecific anti-type IV collagenase antibodies inhibited invasive activity of parental tumor cell lines in the in vitro assay, suggesting a possible causal relationship between the repression of secreted proteases and loss of metastatic properties of the transformants.