Fibroblast Growth Factor-2 Induction of Platelet-derived Growth Factor-C Chain Transcription in Vascular Smooth Muscle Cells Is ERK-dependent but Not JNK-dependent and Mediated by Egr-1

Abstract

Platelet-derived growth factors (PDGFs) play an integral role in normal tissue growth and maintenance as well as many human pathological states including atherosclerosis, fibrosis, and tumorigenesis. The PDGF family of ligands is comprised of A, B, C, and D chains. Here, we provide the first functional characterization of the PDGF-C promoter. We examined 797 bp of the human PDGF-C promoter and identified several putative recognition elements for Sp1, Ets Egr-1, and Smad. The proximal region of the PDGF-C promoter bears a remarkable resemblance to a comparable region of the PDGF-A promoter (1). Binding and transient transfection analysis in primary vascular smooth muscle cells revealed that PDGF-C, like PDGF-A, is under the transcriptional control of the zinc finger nuclear protein Egr-1 (early growth response-1). Electrophoretic mobility shift analysis using both smooth muscle cell nuclear extracts and recombinant protein revealed that Egr-1 and Sp1 bind this region of the PDGF-C promoter (Oligo C, ؊35 to ؊1). Egr-1 competes with Sp1 for overlapping binding sites even when the former is at a stoichiometric disadvantage. Reverse transcriptase PCR and supershift analysis demonstrate that fibroblast growth factor-2 (FGF-2) stimulates both Egr-1 and PDGF-C mRNA expression in a time-dependent and transient manner and that FGF-2-inducible Egr-1 binds the proximal PDGF-C promoter. FGF-2-inducible PDGF-C expression was completely abrogated using catalytic DNA (DNAzymes) targeting Egr-1 but not by its scrambled counterpart. Moreover, using pharmacological inhibitors we demonstrate the critical role of ERK but not JNK in FGF-2-inducible PDGF-C expression. These findings thus demonstrate that PDGF-C transcription, activated by FGF-2, is mediated by Egr-1 and its upstream kinase ERK.

Structural Requirements for Activation of Latent Platelet-derived Growth Factor CC by Tissue Plasminogen Activator

“…In support of our findings it has previously been shown that PAI-1 transcripts are often upregulated in hypoxic conditions and by TGF-␤ 1 treatment, whereas tPA transcripts are down-regulated by hypoxia and differentially regulated by TGF-␤ 1 in a cell-specific context (26 -29). Treatment of the primary fibroblasts with FGF-2, which is known to induce expression of PDGF-C transcripts from vascular smooth muscle cells (30), did not alter the expression of PDGF-C but rather altered the expression of tPA. Taken together these results indicate that the fibroblastic PDGF-CC/tPA growth-stimulatory loop can be regulated by metabolic conditions and other growth factors, which are of importance in the pathophysiology of diabetes.…”

“…regulates PDGF-C transcription in vascular smooth muscle cells (30) it is possible that part of the inhibitory effect of the kringle-2 domain is through binding and subsequent blockage of PDGF-CC activation. Furthermore, we could speculate that upon the interaction of PDGF-CC with kringle-2, the other domains of tPA could interact with molecules such as the low density lipoprotein receptor-related protein, known to both interact with tPA (41) and control PDGFR signaling (42) and thereby facilitating a localized generation of active PDGF-CC.…”

Opposing Actions of Stat1 and Stat6 on IL-13-Induced Up-Regulation of Early Growth Response-1 and Platelet-Derived Growth Factor Ligands in Pulmonary Fibroblasts

“…Egr-1 has been characterized as a transcriptional regulator of both PDGF-A and PDGF-C gene expression (18,19). We sought to determine whether Egr-1 played a role in IL-13-induced up-regulation of PDGF-A or PDGF-C. IL-13-stimulated PDGF-A and PDGF-C mRNA levels were markedly reduced in Egr-1 Ϫ/Ϫ fibroblasts compared with Egr-1 ϩ/ϩ fibroblasts (Fig.…”

“…Egr-1 is an 80-to 82-kDa zinc-finger transcription factor that regulates cell proliferation, differentiation, and apoptosis in response to growth factors, cytokines, oxidative stress, and injury (15)(16)(17). Egr-1 binding to DNA induces expression of isoforms of the PDGF family, including PDGF-A and PDGF-C (18,19). While Egr-1 mediates PDGF expression, PDGF isoforms also stimulate expression of Egr-1, thereby indicating the potential for a mitogenic autocrine loop involving PDGF, PDGFRs, and Egr-1 (17,18).…”

“…In addition, Egr-1-mediated apoptosis was reported as a central feature of TGF-␤ 1 -induced pulmonary fibrosis and alveolar remodeling in mice in vivo (22). Moreover, Egr-1 expression is induced by inflammatory cytokines such as IL-1, TNF-␣, and IFN-␥ (19,20,23). Finally, Egr-1 modulates expression of growth factors, extracellular matrix proteins, and mediators of the leukotriene biosynthesis pathway (24).…”