Interaction of Urokinase-Type Plasminogen Activator with Its Receptor Rapidly Induces Activation of Glucose Transporters

Abstract

The interaction of urokinase-type plasminogen activator (u-PA) or of u-PA amino-terminal fragment (u-PA-ATF) with the cell surface receptor (u-PAR) was found to stimulate an increase of glucose uptake in many cell lines, ranging from normal and transformed human fibroblasts, mouse fibroblasts transfected with human u-PAR, and cells of epidermal origin. Such increase of glucose uptake reached a peak within 5-10 min, depending on the cell line, and occurred through the facilitative glucose transporters (GLUTs), since it was inhibited by cytochalasin B. Each cell line showed a specific mosaic of glucose transporter isoforms, GLUT2 being the most widespread and GLUT1 the most abundant, when present. u-PAR stimulation was followed by translocation of GLUT1 from the microsomal to the membrane compartment, as shown by both immunoblotting and immunofluorescence of sonicated plasma membrane sheets and by activation of GLUT2 on the cell surface. Both translocation and activation resulted inhibitable by protein-tyrosine kinase inhibitors and independent of downregulation of protein kinase C (PKC). The increase of intracellular glucose was followed by neosynthesis of diacylglycerol (DAG) from glucose, as previously shown. Such neosynthesis was completely inhibited by impairment of facilitative GLUT transport by cytochalasin B. DAG neosynthesis was followed by activation of PKC, whose activity translocated into the intracellular compartment (PKM), where it probably phosphorylates substrates required for u-PAR-dependent chemotaxis. Our data show that u-PAR-mediated signal transduction, related with u-PA-induced chemotaxis, involves activation of tyrosine kinase-dependent glucose transporters, leading to increased de novo DAG synthesis from glucose, eventually resulting in activation of PKC.

uPA/uPAR system activation drives a glycolytic phenotype in melanoma cells

“…Such a relation is even more compelling when considering our previous demonstration that following uPA/ uPAR interaction, SV40-transformed human embryonic lung fibroblasts undergo an increase of glucose uptake dependent on translocation of GLUT1 from microsomal to membrane compartment and on GLUT2 activation. 18 A correlation between migration and metabolic switch was recently reported by Bettum et al, 19 showing that in poorly motile melanoma cells the enhanced migration, drives a metabolic change to glycolysis. Thus, we have investigated on the metabolic implications of uPA/uPAR interaction in human melanoma cells, providing evidence that uPAR drives a glycolytic and invasive phenotype in melanoma cells in a EGFRdependent fashion.…”

“…Therefore, anaerobic glycolysis and uPAR overexpression in cancer cells are under the control of the common transcription factor HIF‐1α. Such a relation is even more compelling when considering our previous demonstration that following uPA/uPAR interaction, SV40‐transformed human embryonic lung fibroblasts undergo an increase of glucose uptake dependent on translocation of GLUT1 from microsomal to membrane compartment and on GLUT2 activation . A correlation between migration and metabolic switch was recently reported by Bettum et al ., showing that in poorly motile melanoma cells the enhanced migration, drives a metabolic change to glycolysis.…”

Enhancement of Monoclonal Antibody Production by Lysine‐Containing Peptides

“…Moreover, antibodies can be inhibited or scavenged by soluble antigens (soluble uPAR is often a marker of tumor burden), which can bind to their combining site and prevent attachment to the relevant antigen on the cell surface. uPAR antagonists should be able to impair the multiple interactions of uPAR with uPA, vitronectin, integrins, PAI‐1 and high molecular weight kininogen (all activities intrinsically related to uPAR function in the “grip‐and go” regulation of cell invasion), without exerting any agonistic effect on uPAR, such as chemoinvasion and proliferation29, 30, 31 on the base of structural similarities with the ligand molecule to be displaced.…”

Functions of the Fibrinolytic System in Human Ito Cells and Its Control by Basic Fibroblast and Platelet–Derived Growth Factor

“…However, some data suggest that signaling and activation of a chemotactic and proliferative program may take place upon interaction of u-PAR with a truncated form of u-PA, lacking the catalytic site, or in the presence of inhibitors of plasmin generation. 19,27,42,51,52 Furthermore, it has been shown that u-PAR, which is spatially located in focal contacts and at the leading edge of migrating cells, 53,54 may directly interact via its extracellular domain with activated integrins promoting adhesion and migration toward specific matrix proteins even in the absence of u-PA. 55 Thus, the potential biological interactions of the u-PA/u-PAR system appear more complex than expected and require further studies.…”