Up-regulation of plasminogen activator inhibitor 2 (PAI-2) in response to α-lactalbumin

Abstract

U937 cells, a monocyte-like cell line, are a potent source of plasminogen activator inhibitor 2 (PAI-2) particularly following stimulation with a variety of agents. Lactalbumin enzymatic hydrolysate (LEH) can be used as an alternative to fetal calf serum (FCS) during culture of cells. Here, we report an up-regulation of PAI-2 synthesis following treatment of U937 cells with LEH and purified α-lactalbumin. Secretion of PAI-2 antigen into the culture medium was found to increase over time following growth of U937 cells in medium containing LEH (1 %) compared to medium alone or containing FCS. The possibility that undigested lactalbumin was present in LEH was then examined. A potent increase in secreted and intracellular PAI-2 was seen following stimulation of U937 cells with purified α-lactalbumin. This effect was both dose- and time-dependent. Northern blotting confirmed that the up-regulation in PAI-2 was at the level of mRNA. Basal levels of PAI-2 were up-regulated by an analogue of CAMP, whereas there was no further effect on α-lactalbumin stimulated PAI-2. Lactalbumin is another agent that up-regulates the synthesis of PAI-2, an effect that influences the study of PAI-2 in cultured cells.