Interaction of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) with induced adipocyte differentiation in mouse embryonic fibroblasts (MEFs) involves tyrosine kinase c-Src.
Adipocyte differentiation of mouse embryonic fibroblasts (MEFs) derived from c-Src wild-type or c-Src-deficient (abbreviated as MEF+/+ and MEF-/- hereafter) C57BL/6 mice was induced by ascorbic acid (A) and beta-glycerophosphate (G). TCDD clearly suppressed differentiation of MEF+/+, but not MEF-/-, as measured by increased accumulation of triglycerides associated with increased expression of adipocyte differentiation-specific genes such as peroxisome proliferators activated receptor (PPAR)gamma, stearoyl-CoA desaturase (SCD-1). Studies on inducibility of TCDD-activated genes such as cytochrome P450 (CYP)1A1 and CYP1B1 revealed a comparable dose response in both MEF+/+ and MEF-/-. Furthermore, the binding activity of AhR complexes to xenobiotic response elements (XREs) was similar in both cell lines. We further studied the effect of TCDD on CCAAT/enhancer binding proteins (C/EBP), which are known to be important regulators of cell differentiation. TCDD induced C/EBPbeta and C/EBPdelta mRNA expression and DNA binding activity in a time- and dose-dependent manner in MEF+/+ but not in MEF-/-. The levels of C/EBPbeta and C/EBPdelta were still elevated in differentiated MEF+/+ after 10 days of treatment with TCDD. In MEF-/-, C/EBPbeta and C/EBPdelta are highly expressed constitutively. In contrast to MEF+/+, TCDD does not cause any significant change of these transcription factors in MEF-/-. These data indicate that suppression of differentiation by TCDD in MEF requires a functional c-Src activity and induced levels of C/EBPbeta and C/EBPdelta, including their maintenance at high levels by TCDD, rather than ultimate high levels of these C/EBP isoforms.
D017667:Adipocytes / Q000166:cytology / Q000187:drug effects*; D000818:Animals; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D051743:CCAAT-Enhancer-Binding Protein-delta; D022762:CCAAT-Enhancer-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology; D000081247:CSK Tyrosine-Protein Kinase; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D002454:Cell Differentiation / Q000187:drug effects*; D004247:DNA / Q000187:drug effects / Q000378:metabolism; D004622:Embryo, Mammalian; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects; D015870:Gene Expression / Q000187:drug effects*; D051379:Mice; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology*; D011505:Protein-Tyrosine Kinases / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D012333:RNA, Messenger / Q000096:biosynthesis / Q000187:drug effects; D018336:Receptors, Aryl Hydrocarbon / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D013230:Stearoyl-CoA Desaturase; D014157:Transcription Factors / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D019061:src-Family Kinases
D022782:CCAAT-Enhancer-Binding Protein-beta; D022762:CCAAT-Enhancer-Binding Proteins; C497253:Cebpd protein, mouse; D018797:Cell Cycle Proteins; D000072317:Polychlorinated Dibenzodioxins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D051743:CCAAT-Enhancer-Binding Protein-delta; D004247:DNA; C490333:Scd1 protein, mouse; D013230:Stearoyl-CoA Desaturase; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D019061:src-Family Kinases