Z Gastroenterol 2010; 48 - P1_05
DOI: 10.1055/s-0029-1246336

TGF-β/Smad-1 signaling activates regenerative pro-survival mechanisms, whereas TGF-β/Smad-2/3 leads to pro-apoptotic programs in primary mouse hepatocytes

K Breitkopf 1, A Müller 2, I Ilkavets 2, S Dooley 3
  • 1Molekulare Alkoholforschung in der Gastroenterologie; Med. Klinik II; Universitätsmedizin Mannheim; Universität Heidelberg; Mannheim, Mannheim
  • 2Molecular Alcohol Research in Gastroenterology, Department of Medicine II, Faculty of Medicine at Mannheim, University of Heidelberg, Mannheim
  • 3II. Med. Universitätsklinik (Gastroenterologie, Hepatologie & Infektionskrankheiten), Mannheim

Phosphorylation of the signaling molecules Smad2/3 is considered as classical TGF-β signal transduction pathway. However, in an increasing number of cell types, including endothelial cells, hepatocytes and hepatic stellate cells, TGF-β phosphorylates Smad1, originally dedicated as BMP responsive branch. Since no discrimination of these parallel pathways was done up to now in liver cells, aim of the present study was to identify TGF-β/Smad1 target genes in cultured hepatocytes. Using microarray technology, TGF-β regulated early-response genes were identified either under control conditions or after adenoviral overexpression of Smad6, a specific inhibitor of Smad1 phosphorylation, which does not affect Smad2/3. Additionally TGF-β regulated genes were identified upon overexpression of Smad7, which blocks phosphorylation of all three Smads. With this experimental setup TGF-β/Smad1 targets could be distinguished from Smad2/3 and non-Smad target genes. TGF-β induced 53 genes within 1h by greater or equal to 1.6-fold and down-regulated 10 genes. Those genes which were mainly regulated via the Smad1 pathway included proteins involved in proliferation, differentiation, EMT (e.g. Id1, -2, -3, PDGF-A and –B, Snai1) as well as inhibitory proteins like Smad6 itself, Cish or the TGF-β pseudo-receptor Bambi. One of the strongest induced TGF-β/Smad1 target genes was the iron regulatory hormone hepcidin and the strongest down-regulated target gene was the cytochrome P450 1a1 (Cyp1a1). In summary, our data show that (i) TGF-β regulates a huge number of target genes within only 1 hour, (ii) the most strongly regulated genes (Id1, hepcidin, Id3, Cyp1a1) belong to the group of Smad1 targets and (iii) pro-apoptotic genes like Jun-B, Fos-B and Tieg1 are Smad2/3 regulated, implying that the alternative TGF-β/Smad1 route relates more to cell survival and regeneration. These findings explain to some extent the frequently observed opposing effects of TGF-β, e.g. on proliferation or apoptosis.