Concomitant secretion by A431 cells of tissue plasminogen activator and a specific inhibitor masks EGF modulation of tPA activity.
It has previously been reported that EGF enhances uPA but not tPA in the A431 squamous carcinoma cell line. To determine whether the absence of tPA modulation by EGF reflected steady levels or the action of an anti-activator, we assayed tPA, PAI-1 and tPA/PAI-1 complexes by zymography and immunological assays. Under conditions in which EGF had no effect on tPA activity, tPA antigen paradoxically increased with a concomitant rise of tPA/PAI-1 complexes. This indicated that tPA was rapidly inactivated through the formation of a complex, immunologically and electrophoretically related to tPA/PAI-1. tPA antigen and tPA/PAI-1 complexes were modulated by EGF in a time and concentration dependent manner. PAI-1 antigen was secreted into A431 medium (CM) after a lag phase of 16 h in both control and EGF-treated cultures. Evidence is presented here that two forms of PAI-1 are present in A431 CM: an inactive form and an active form which neutralizes the tPA secreted, masking its enhancement by EGF in functional assays.
George
F
F
Hematology Laboratory, Faculty of Pharmacy, Marseille, France.
Pourreau-Schneider
N
N
Arnoux
D
D
Boutière
B
B
Berthois
Y
Y
Martin
P M
PM
Sampol
J
J
D004591:Electrophoresis, Polyacrylamide Gel; D004815:Epidermal Growth Factor / Q000502:physiology*; D006801:Humans; D015849:Plasminogen Inactivators / Q000378:metabolism*; D013997:Time Factors; D010959:Tissue Plasminogen Activator / Q000378:metabolism* / Q000502:physiology; D014407:Tumor Cells, Cultured
D015849:Plasminogen Inactivators; D004815:Epidermal Growth Factor; D010959:Tissue Plasminogen Activator