Transcriptional and post-transcriptional regulation of the receptor for urokinase-type plasminogen activator by cytokines and tumour promoters in the human lung carcinoma cell line A549

Abstract

The receptor for urokinase-type plasminogen activator (uPAR) is an integral membrane protein that specifically binds urokinase-type plasminogen activator (uPA) and plays a crucial role in cell surface plasmin generation. We have previously found that transforming growth factor-beta, type 1 (TGF-beta 1), increases uPAR gene transcription in the human lung carcinoma cell line A549 and now report that also epidermal growth factor (EGF) and the tumour promoter phorbol 12-myristate 13-acetate (PMA) cause increased uPAR transcription and that PMA and TGF-beta 1 in addition increase the stability of uPAR mRNA, while EGF has no effect on this parameter. All three compounds also increase the uPAR protein level, as measured by cell-binding experiments with radiolabelled ligand. The increase in uPAR protein level was however considerably lower with all three compounds than the increase in mRNA level, suggesting that they also exert a translational or post-translational control. Accompanying the increase in the number of uPAR molecules there was a proportional decrease in their ligand-binding affinity, the mechanism of which is unknown. Platelet-derived growth factor, basic fibroblast growth factor and cyclic AMP analogues did not induce any change in the uPAR mRNA level in A549 cells. Previous studies have shown that expression of uPA and its type-1 inhibitor is regulated by a variety of cytokines in a cell-specific manner. The present study indicates that cytokines in addition influence cell surface plasminogen activation by regulating uPAR expression.

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

“…However, the mechanism(s) by which the u-PAR gene is overexpressed is unclear at the present time. Since phorbol ester and a variety of growth factors including EGF, FGF, and vEGF, which up-regulate u-PAR synthesis, stimulate ERK activity (Zohn et al, 1995;Wiese et al, 1995;Bogoyevitch et al, 1994;Campbell et al, 1995;Jones et al, 1994;Lund et al, 1995), we undertook a study to determine the role of these MAPKs in regulating u-PAR expression in two cultured colon cancer cell lines. Several observations suggested a role for an ERK1-dependent signaling cascade in the regulation of u-PAR expression.…”

“…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.…”

“…Further, the increased u-PAR display by the RKO cells is a direct consequence of transcriptional activation of the gene as shown by nuclear run on experiments (Wang et al, 1994) (Mignatti et al, 1991;Lund et al, 1995;Je ers et al, 1996). Since all of these agents increase extracellular signal-regulated kinase (ERK) activity (Fabian et al, 1993;Bogoyevitch et al, 1994;Tsai et al, 1995), the objective of the current study was to determine the role of ERK1 and ERK2 in regulating u-PAR expression in these two colon cancer cell lines.…”

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

“…Transcription of the u-PAR gene gives rise to a 1.4 kb mRNA or an alternatively spliced variant lacking the membrane attachment peptide sequence (Roldan et al, 1990;Pyke et al, 1993). The amounts of u-PAR are controlled mainly at the transcriptional level through 398 base pairs of upstream sequence but altered message stability and receptor recycling may represent other means of controlling the amount of this gene product at the cell surface (Lengyel et al, 1996;Shetty et al, 1997;Lund et al, 1995;Nykjaer et al, 1997).…”

Soluble urokinase plasminogen activator receptor—A valuable biomarker in systemic lupus erythematosus?

“…The expression of uPAR is mainly regulated by growth factors and pro-inflammatory cytokines like basic fibroblast growth factor, epidermal growth factor, tumor necrosis factor, interleukin (IL) -1β and IL-6 [33][34][35][36][37][38] and the major formation of suPAR is mediated via shedding of uPAR from the plasma membrane. Although an alternative splicing of uPAR messenger RNA has been demonstrated, resulting also in synthesis of uPAR without a GPI-anchoring site [39], the relative impact of this suPAR source is unclear.…”