Summary
In a number of cancer types high tumor tissue levels of plasminogen activator inhibitor
type 1 (PAI-1) protein are strongly associated with shorter cancer patient survival.
This association has been intriguing since PAI-1 is known to inhibit urokinase plasminogen
activator (uPA) that converts plasminogen to plasmin, which is actively involved in
tumor progression and invasion. In order to further explore the biological role of
PAI-1 in cancer, we have prepared fibroblasts from PAI-1 gene deficient mice and from
their wild type littermates. From these fibroblasts fibrosarcoma cell lines were established
and characterized. Both types of fibroblasts underwent spontaneous transformation
as indicated by aneuploidy, immortalization, clonogenicity in soft agar and tumor
formationin vivo. While both PAI-1 deficient and PAI-1 expressing cell lines showed similar proliferation
ratesin vitro, cells devoid of PAI-1 were significantly more sensitive to apoptotic stimuli. When
inoculated subcutaneously into nude mice PAI-1 expressing cells rapidly established
tumors, while PAI-1 deficient cells had a significantly longer lag-phase before they
started to grow (p<0.0001). The present study suggests that PAI-1,besides its uPA
inhibiting function, has a role in cancer progression by protecting tumor cells from
undergoing apoptosis.
Keywords
PAI-1 - murine fibrosarcoma cell lines - apoptosis