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

U937 cells, a monocyte-like cell line, are a potent source of plasminogen a ctivator inhibitor 2 (PAI-2) particularly following stimulation with a vari ety of agents. Lactalbumin enzymatic hydrolysate (LEH) can be used as an al ternative to fetal calf serum (FCS) during culture of cells. Here, we repor t an up-regulation of PAI-2 synthesis following treatment of U937 cells wit h LEH and purified alpha-lactalbumin. Secretion of PAI-2 antigen into the c ulture medium was found to increase over time following growth of U937 cell s in medium containing LEH (1%) compared to medium alone or containing FCS. The possibility that undigested lactalbumin was present in LEH was then ex amined. A potent increase in secreted and intracellular PAI-2 was seen foll owing stimulation of U937 cells with purified alpha-lactalbumin. This effec t was both dose- and time-dependent. Northern blotting confirmed that the u p-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 alpha-lactalbumin stimulated PAI-2. Lactalbumin is another agent that up-r egulates the synthesis of PAI-2, an effect that influences the study of PAI -2 in cultured cells.