TGF-beta receptor-mediated signalling through Smad2, Smad3 and Smad4

Abstract

Smad family members are newly identified essential intracellular signalling components of the transforming growth factor‐β (TGF‐β) superfamily. Smad2 and Smad3 are structurally highly similar and mediate TGF‐β signals. Smad4 is distantly related to Smads 2 and 3, and forms a heteromeric complex with Smad2 after TGF‐β or activin stimulation. Here we show that Smad2 and Smad3 interacted with the kinase‐deficient TGF‐β type I receptor (TβR)‐I after it was phosphorylated by TβR‐II kinase. TGF‐β1 induced phosphorylation of Smad2 and Smad3 in Mv1Lu mink lung epithelial cells. Smad4 was found to be constitutively phosphorylated in Mv1Lu cells, the phosphorylation level remaining unchanged upon TGF‐β1 stimulation. Similar results were obtained using HSC4 cells, which are also growth‐inhibited by TGF‐β. Smads 2 and 3 interacted with Smad4 after TβR activation in transfected COS cells. In addition, we observed TβR‐activation‐dependent interaction between Smad2 and Smad3. Smads 2, 3 and 4 accumulated in the nucleus upon TGF‐β1 treatment in Mv1Lu cells, and showed a synergistic effect in a transcriptional reporter assay using the TGF‐β‐inducible plasminogen activator inhibitor‐1 promoter. Dominant‐negative Smad3 inhibited the transcriptional synergistic response by Smad2 and Smad4. These data suggest that TGF‐β induces heteromeric complexes of Smads 2, 3 and 4, and their concomitant translocation to the nucleus, which is required for efficient TGF‐β signal transduction.

Intestinal intraepithelial lymphocytes prevent pathogen‐driven inflammation and regulate the Smad/T‐bet pathway of lamina propria CD4+ T cells

“…Here we show that Smad2, Smad3 and Smad4 are up-regulated in the LP CD4 + T lymphocytes isolated from the mice protected by the adoptive transfer of TGF-gproducing IEL. Smad7, which is up-regulated by TNF- § , IL-1 g , IFN-+ and CD40 ligation, is an inhibitor of the TGFg signaling pathway that interacts with the activating Smad2-Smad3 complex [28,29]. The expression of Smad7 increases in those mice that produce high level of IFN-+ and develop the ileitis.…”

Novel antisense oligonucleotides targeting TGF-β inhibit in vivo scarring and improve surgical outcome

“…50,51 TbR-I and TbR-II are now believed to initiate signal transduction by involving Smad2 and Smad3. 49,[52][53][54] Although less well understood, all three TGF-b isoforms are believed to bind to TbR-II, although TGF-b1 has the greatest affinity. A recent finding has been that TbR-IIB, an alternatively spliced …”

ELAC2, a putative prostate cancer susceptibility gene product, potentiates TGF-β/Smad-induced growth arrest of prostate cells

“…When we explored if ELAC2 can activate the TGF-b/Smad3-dependent promoter, ELAC2 could also potentiate the activity of (CAGA) 12 -luc upon ALK5 activation in dose-dependent manner ( Figure 1d). As Smad2 can make ternary complex with Smad3 and Smad4 upon TGF-b stimulation and activate TGF-b-induced promoter (Nakao et al, 1998), ELAC2 presumably interacts with Smad3/Smad4 complex via its binding to Smad2 to enhance ALK5ca-induced (CAGA) 12 -luc activity. To examine if ELAC2 can promote TGF-b signaling in the absence of Smad4, we used MDA-MB468 cells that lack Smad4.…”