title: Crosstalk between PDGF and IGF-I receptors in rat liver myofibroblasts: implication for liver fibrogenesis.
abstract: Insulin-like growth factor I (IGF-I) and platelet-derived growth factor (PDGF) have been identified as significant mitogens for liver myofibroblasts (LMFs), one of the cell populations playing a role in liver fibrogenesis. In the present work, we aimed to elucidate a possible interaction between PDGF receptor (PDGFR) and IGF-I receptor (IGF-IR) signaling in LMFs. Among different rat liver cells, PDGFR alpha- and beta-subunits were mainly expressed in hepatic stellate cells and LMFs, and were upregulated during their in vitro cultivation. In LMFs, PDGF-BB (10 ng/ml) stimulated DNA synthesis approximately two-fold and this effect was similar to that of IGF-I. IGF-I and PDGF-BB differentially affected IGF-IR and PDGFR signaling. High concentrations of IGF-I decreased levels of IGF-IR and IRS-1 and inhibited the expression and activation of PDGFRalpha. PDGF-BB prevented IGF-I-induced downregulation of the IGF-IR, but did not affect expression of its cognate receptor subunits. Transphosphorylation of PDGFR and IGF-IR was not observed. PDGF effectively activated terminal MAP kinases, PI3 kinase and Akt kinase, whereas IGF-I demonstrated weaker effects. PLCgamma(1) was phosphorylated only in response to PDGF, but not to IGF-I. In rat LMFs, blockade of the IGF-IR via inhibition of the IGF-IR kinase completely abrogated IGF- and PDGF-induced mitogenesis and the ability of PDGF to phosphorylate PLCgamma(1). In conclusion, the presented data demonstrate that the PDGFR signaling requires a functional IGF-IR and that PDGF-BB stabilizes the IGF-IR function through preventing the IGF-I-induced downregulation of the IGF-IR. These interactions might be relevant in vivo for the fibroproliferative response during liver injury.
authors.affiliation: Department of Medicine, Division of Gastroenterology and Endocrinology, Georg-August-Universität, Göttingen, Germany.
authors.forename: Ruslan
authors.initials: R
authors.lastname: Novosyadlyy
authors.forename: Jozsef
authors.initials: J
authors.lastname: Dudas
authors.forename: Rajeswararao
authors.initials: R
authors.lastname: Pannem
authors.forename: Giuliano
authors.initials: G
authors.lastname: Ramadori
authors.forename: Jens-Gerd
authors.initials: JG
authors.lastname: Scharf
mesh_terms: D000818:Animals; D000077214:Becaplermin; D018929:Cell Culture Techniques; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005355:Fibrosis / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D008099:Liver / Q000166:cytology*; D008103:Liver Cirrhosis / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000737:chemistry / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D020574:Proto-Oncogene Proteins c-sis; D051381:Rats; D017208:Rats, Wistar; D020239:Receptor Cross-Talk / Q000502:physiology*; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D020796:Receptor, Platelet-Derived Growth Factor alpha / Q000037:antagonists & inhibitors; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism*
chemical_list: D055504:Insulin Receptor Substrate Proteins; C526296:Irs1 protein, rat; D010750:Phosphoproteins; D010982:Platelet-Derived Growth Factor; D020574:Proto-Oncogene Proteins c-sis; D000077214:Becaplermin; D007334:Insulin-Like Growth Factor I; D004247:DNA; D019869:Phosphatidylinositol 3-Kinases; D017526:Receptor, IGF Type 1; D020796:Receptor, Platelet-Derived Growth Factor alpha; D017479:Receptors, Platelet-Derived Growth Factor; D051057:Proto-Oncogene Proteins c-akt; D020928:Mitogen-Activated Protein Kinases