Upregulation of urokinase receptor expression on migrating endothelial cells

Abstract

Abstract. One of the phenotypic hallmarks of migrating endothelial cells, both in vivo and in vitro, is expression of the urokinase-type plasminogen activator (u-PA), a key mediator of extracellular proteolysis. In the study reported here, we have used an in vitro model of endothelial cell migration to explore the mechanism of this phenomenon. We have found that wounding of an endothelial cell monolayer triggers a marked, rapid and sustained increase in expression of a specific high-affinity receptor for u-PA (u-PAr) on the surface of migrating cells. Migrating cells displayed an increase in the levels of u-PA and u-PAr mRNAs, and this increase was mediated by endogenous basic fibroblast growth factor (bFGF). We also show that the increase in u-PA activity on migrating ceils can be accounted for by an increase in receptorbound u-PA, and that the increase in activity is also dependent on endogenous bFGF. These results demonstrate that the expression of plasmin-mediated proteolytic activity by migrating endothelial cells is a consequence of increased production of both u-PA and its receptor, and that this in turn is mediated by endogenous bFGE This suggests that u-PA, produced at increased levels by migrating cells, binds to u-PAr whose expression is upregulated on the same cells. These observations are in accord with the postulated role of u-PAr in mediating efficient and spatially restricted extracellular proteolysis, particularly in the context of cell migration. T i-m vascular endothelium consists of a highly ordered monolayer of quiescent non-migrating cells, which can be induced to migrate and replicate in a number of physiological and pathological settings. This occurs for example during angiogenesis in which new capillary blood vessels are formed from preexisting vessels in response to angiogenic stimuli. During this process, microvascular endothelial cells locally degrade their basement membrane, and subsequently invade the surrounding interstitial extracellular matrix within which they form a capillary sprout. The sprout develops into a functional vessel after formation of a lumen (reviewed by DAmore and Thompson, 1987;Zetter, 1988).To breach the mechanical barriers imposed by the basement membrane and surrounding extracellular matrix, endothelial cells use limited proteolytic degradation of matrix components at regions of contact with the cell surface (reviewed by Moscatelli and Rifldn, 1988;Pepper and Montesano, 1991). Plasminogen activators (PAs) ~ are key mediators in this respect; they convert the widely distributed and

Stimulation of urokinase-type plasminogen activator receptor expression by PMA requires JNK1-dependent and -independent signaling modules

“…For example, subsequent to injury, regenerating epithelial outgrowths express u-PAR mRNA in keratinocytes at the leading edge (Romer et al, 1994). Similarly, wounded endothelial cells in monolayer rapidly up-regulate their u-PAR expression (Pepper et al, 1993). In cancer, it appears that the u-PAR plays a prominent role in tumor cell invasion and metastasis and this may very well represent an extension of its physiological role as described previously.…”

Anthocyanidins inhibit migration of glioblastoma cells: Structure‐activity relationship and involvement of the plasminolytic system

“…During migration of several cell types, expression of uPA, uPAR, and PAI-1 is upregulated [Pepper et al, 1993;Andreasen et al, 1997;Chazaud et al, 2000]. Results with many different human cancers have shown that high levels of uPA, uPAR, and PAI-1 in tumors are correlated with poor patient prognosis [Andreasen et al, 1997].…”

Elevated urokinase-type plasminogen activator receptor expression in a colon cancer cell line is due to a constitutively activated extracellular signal-regulated kinase-1-dependent signaling cascade

“…While RKO cells did not contain a mutation-activated K-Ras, it is still possible that the activation of the ERK1-dependent signaling cascade is a consequence of Ras recruitment by a growth factoractivated receptor protein tyrosine kinase at the cell surface (Stacey et al, 1991). Indeed, several studies have convincingly shown that a variety of growth factors including EGF (Lund et al, 1995), vascular endothelial growth factor (vEGF) (Mandriota et al, 1995) and FGF (Pepper et al, 1993) all induce u-PAR expression. Alternatively, it is equally plausible that the constitutive activation of ERK1 in RKO cells is a consequence of (a) protein kinase C b stimulation (Sauma et al, 1996), (b) a reduced activity/amount of K-Rev (Kitayama et al, 1989), which is an endogenous inhibitor of Ras, or (c) lower activity/ amounts of phosphatases such as CL100, HVH2 or MKP-3 (Alessi et al, 1993;Guan and Butch, 1995;Muda et al, 1996) which function to return cells to the quiescent state (Dent et al, 1995) following their stimulation with growth factors.…”

“…The signal was strongest in the keratinocytes just beginning to move 12 h after wounding. Likewise, wounding of an endothelial cell monolayer triggers a rapid and sustained increase in u-PAR expression at the surface of the migrating cells and this increase is mediated by endogenous ®broblast growth factor (FGF) (Pepper et al, 1993). In a number of cancers, the expression of the u-PAR is required for the invasive phenotype (Quattrone et al, 1995;Kariko et al, 1993;Kook et al, 1994) and for colon cancer a high u-PAR level portends a low 5 year survival rate (Ganesh et al, 1994).…”