Hepatocyte growth factor-stimulated renal tubular mitogenesis: effects on expression of c-myc, c-fos, c-met, VEGF and the VHL tumour-suppressor and related genes

Abstract

Hepatocyte growth factor (HGF/SF) is a potent renal proximal tubular cell (PTEC) mitogen involved in renal development. HGF/SF is the functional ligand for the c-met proto-oncogene, and germline c-met mutations are associated with familial papillary renal cell carcinoma. Somatic von Hippel-Lindau disease tumour-suppressor gene (VHL) mutations are frequently detected in sporadic clear cell renal cell carcinomas (RCC), and germline VHL mutations are the commonest cause of familial clear cell RCC. pVHL binds to the positive regulatory components of the trimeric elongin (SIII) complex (elongins B and C) and has been observed to deregulate expression of the vascular endothelial growth factor (VEGF) gene. HGF/SF has similarly been reported to up-regulate expression of the VEGF gene in non-renal experimental systems. To investigate the mechanism of HGF/SF action in PTECs and, specifically, to examine potential interactions between the HGF/c-met and the VHL-mediated pathways for renal tubular growth control, we have isolated untransformed PTECs from normal kidneys, developed conditions for their culture in vitro and used these cells to investigate changes in mRNA levels of the VHL, elongin A, B and C, VEGF, c-myc, c-fos and c-met genes after HGF/SF exposure. Significant elevations in the mRNA levels of VEGF, c-myc, c-fos, c-met and elongins A, B and C, but not VHL, were detected after HGF/SF stimulation of human PTECs (P < 0.02), with a consistent order of peak levels observed over successive replicates (c-fos at 1 h, VEGF at 2-4 h, c-myc, at 4 h, followed by c-met and all three elongin subunits at 8 h). This study highlights the spectrum of changes in gene expression observed in PTECs after HGF/SF stimulation and has identified possible candidate mediators of the HGF/SF-induced mitogenic response. Our evidence would suggest that the changes in PTEC VEGF expression induced by HGF/SF are mediated by a VHL-independent pathway. Images Figure 1

Genetic and functional analysis of the von Hippel-Lindau (VHL) tumour suppressor gene promoter

“…49 Binding of E2F1 to the VHL promoter might suggest that VHL promoter activity was cell cycle dependent; however, evidence for cell cycle dependent variations of VHL transcription have not been reported. 50 In summary we have identified a significant positive regulatory element for VHL promoter activity as an Sp1 binding site at nt +1 and +11, and mapped another positive regulatory region element between nt −49 and −19. This latter region was shown specifically to bind as yet unidentified factors, VHL-TF1 and VHL-TF2, which were confirmed not to be E2F-1.…”

Increased Sp1 phosphorylation as a mechanism of hepatocyte growth factor (HGF/SF)-induced vascular endothelial growth factor (VEGF/VPF) transcription

“…HGF/SF is a known angiogenesis factor discovered primarily through its direct effects on endothelial cell motility and capillary tube formation in vitro and its ability to induce angiogenesis in vivo (reviewed by Rosen and Goldberg, 1997). As a key paracrine mediator of mesenchymal epithelial interactions (reviewed by Birchmeier and Birchmeier, 1994;Rosen et al, 1994), its ability to induce VEGF/VPF expression in different cell types (Clifford et al, 1998;Moriyama et al, 1998) and to potentiate its angiogenic effect via paracrine upregulation of VEGF/VPF in vivo (Van Belle et al, 1998) strongly supports a model of an indirect amplification loop of angiogenesis. We therefore intended to elucidate the molecular mechanisms employed to mediate HGF/SF-induced VEGF/VPF gene expression.…”

“…HGF/SF mediates its effects through binding to the Met receptor tyrosine kinase, which is predominantly expressed on cells of epithelial origin, suggesting a key role for HGF/SF as a paracrine mediator of mesenchyme-epithelial interactions (reviewed by Birchmeier and Birchmeier, 1994;Rosen et al, 1994). On the basis of its ability to induce VEGF/VPF expression in different cell types (Clifford et al, 1998;Moriyama et al, 1998), and to potentiate its angiogenic effect via upregulation of VEGF/VPF in vivo (Van Belle et al, 1998), a model of an indirect paracrine amplification loop of angiogenesis has been proposed.…”

Inhibition of Insulin-like Growth Factor-I-mediated Cell Signaling by the von Hippel-Lindau Gene Product in Renal Cancer

“…have mainly focused on identifying molecular prognostic factors, including growth factors (1,2), oncogenes (3,4), cell adhesion molecules (5,6), and proteases (7,8), that may provide insights into the mechanism of the cancer and its subsequent treatment. Insulin-like growth factors (IGFs) are candidate proliferation markers in renal cell carcinoma because of their overall importance in embryonic and somatic growth, differentiation, and tumorigenesis (9,10) and because of their particular importance in renal growth and development (11,12).…”