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TGFbeta1 signaling via alphaVbeta6 integrin.

Kracklauer MP, Schmidt C, Sclabas GM - Mol. Cancer (2003)

Bottom Line: Our data provide support for the existence of an alternate TGFbeta1 signaling pathway that is independent of the known SMAD pathway.This alternate pathway involves alphaVbeta6 integrin and the Ras/MAP kinase pathway and does not employ an RGD motif in TGFbeta1-sensitive tumor cells.The combined action of these two pathways seems to be necessary to elicit a complete TGFbeta1 signal.

View Article: PubMed Central - HTML - PubMed

Affiliation: Section of Molecular Cell and Developmental Biology, Institute for Cellular and Molecular Biology, The University of Texas at Austin, 1 University Station, A4800, 78712, Austin, TX, USA. mordechai30@hotmail.com

ABSTRACT

Background: Transforming growth factor beta1 (TGFbeta1) is a potent inhibitor of epithelial cell growth, thus playing an important role in tissue homeostasis. Most carcinoma cells exhibit a reduced sensitivity for TGFbeta1 mediated growth inhibition, suggesting TGFbeta1 participation in the development of these cancers. The tumor suppressor gene DPC4/SMAD4, which is frequently inactivated in carcinoma cells, has been described as a key player in TGFbeta1 mediated growth inhibition. However, some carcinoma cells lacking functional SMAD4 are sensitive to TGFbeta1 induced growth inhibition, thus requiring a SMAD4 independent TGFbeta1 pathway.

Results: Here we report that mature TGFbeta1 is a ligand for the integrin alphaVbeta6, independent of the common integrin binding sequence motif RGD. After TGFbeta1 binds to alphaVbeta6 integrin, different signaling proteins are activated in TGFbeta1-sensitive carcinoma cells, but not in cells that are insensitive to TGFbeta1. Among others, interaction of TGFbeta1 with the alphaVbeta6 integrin resulted in an upregulation of the cell cycle inhibitors p21/WAF1 and p27 leading to growth inhibition in SMAD4 deleted as well as in SMAD4 wildtype carcinoma cells.

Conclusions: Our data provide support for the existence of an alternate TGFbeta1 signaling pathway that is independent of the known SMAD pathway. This alternate pathway involves alphaVbeta6 integrin and the Ras/MAP kinase pathway and does not employ an RGD motif in TGFbeta1-sensitive tumor cells. The combined action of these two pathways seems to be necessary to elicit a complete TGFbeta1 signal.

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Cell cycle genes in response to TGFβ1. Western Blot analysis of MCF-7 and MDA-MB 231 cells as indicated after stimulation with TGFβ1 for the time indicated. Cytoskeletally anchored proteins are differentially marked. In part the cells were preincubated with αV- and β6-antibodies (1:100 each for 30 min), with a TGFβ-RII antibody (15 μg/ml for 30 min), cytochalasin D, BAPTA AM and MEK1 inhibitor PD98059, respectively.
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Figure 7: Cell cycle genes in response to TGFβ1. Western Blot analysis of MCF-7 and MDA-MB 231 cells as indicated after stimulation with TGFβ1 for the time indicated. Cytoskeletally anchored proteins are differentially marked. In part the cells were preincubated with αV- and β6-antibodies (1:100 each for 30 min), with a TGFβ-RII antibody (15 μg/ml for 30 min), cytochalasin D, BAPTA AM and MEK1 inhibitor PD98059, respectively.

Mentions: In order to test whether TGFβ1 signaling via αVβ6 is specific for SMAD4 deleted BxPC-3 cells or if this is a general phenomenon, we investigated signaling in TGFβ1-sensitive carcinoma cell lines HeLa, MCF-7 and MDA-MB-231. TGFβ1 induced recruitment of p125Fak, p130Cas and Sos1/2 to the cytoskeleton. Enhanced expression of c-jun, c-fos, p21WAF1 and p27KIP, while downregulating PCNA, is dependent on ERK1/2 signaling, an intact cytoskeleton and intracellular calcium (Figures 5, 6A, 7, 8 and additional files 6, 7 and 8). We also confirmed the purity of the commercially available mature TGFβ1 used in these experiments by silver stained non-reducing SDS-PAGE, with latent TGFβ1 as control (Figure 6B). We also demonstrated the SMAD4 deficiency of the BxPC-3 cells used (Figure 6C).


TGFbeta1 signaling via alphaVbeta6 integrin.

Kracklauer MP, Schmidt C, Sclabas GM - Mol. Cancer (2003)

Cell cycle genes in response to TGFβ1. Western Blot analysis of MCF-7 and MDA-MB 231 cells as indicated after stimulation with TGFβ1 for the time indicated. Cytoskeletally anchored proteins are differentially marked. In part the cells were preincubated with αV- and β6-antibodies (1:100 each for 30 min), with a TGFβ-RII antibody (15 μg/ml for 30 min), cytochalasin D, BAPTA AM and MEK1 inhibitor PD98059, respectively.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC184456&req=5

Figure 7: Cell cycle genes in response to TGFβ1. Western Blot analysis of MCF-7 and MDA-MB 231 cells as indicated after stimulation with TGFβ1 for the time indicated. Cytoskeletally anchored proteins are differentially marked. In part the cells were preincubated with αV- and β6-antibodies (1:100 each for 30 min), with a TGFβ-RII antibody (15 μg/ml for 30 min), cytochalasin D, BAPTA AM and MEK1 inhibitor PD98059, respectively.
Mentions: In order to test whether TGFβ1 signaling via αVβ6 is specific for SMAD4 deleted BxPC-3 cells or if this is a general phenomenon, we investigated signaling in TGFβ1-sensitive carcinoma cell lines HeLa, MCF-7 and MDA-MB-231. TGFβ1 induced recruitment of p125Fak, p130Cas and Sos1/2 to the cytoskeleton. Enhanced expression of c-jun, c-fos, p21WAF1 and p27KIP, while downregulating PCNA, is dependent on ERK1/2 signaling, an intact cytoskeleton and intracellular calcium (Figures 5, 6A, 7, 8 and additional files 6, 7 and 8). We also confirmed the purity of the commercially available mature TGFβ1 used in these experiments by silver stained non-reducing SDS-PAGE, with latent TGFβ1 as control (Figure 6B). We also demonstrated the SMAD4 deficiency of the BxPC-3 cells used (Figure 6C).

Bottom Line: Our data provide support for the existence of an alternate TGFbeta1 signaling pathway that is independent of the known SMAD pathway.This alternate pathway involves alphaVbeta6 integrin and the Ras/MAP kinase pathway and does not employ an RGD motif in TGFbeta1-sensitive tumor cells.The combined action of these two pathways seems to be necessary to elicit a complete TGFbeta1 signal.

View Article: PubMed Central - HTML - PubMed

Affiliation: Section of Molecular Cell and Developmental Biology, Institute for Cellular and Molecular Biology, The University of Texas at Austin, 1 University Station, A4800, 78712, Austin, TX, USA. mordechai30@hotmail.com

ABSTRACT

Background: Transforming growth factor beta1 (TGFbeta1) is a potent inhibitor of epithelial cell growth, thus playing an important role in tissue homeostasis. Most carcinoma cells exhibit a reduced sensitivity for TGFbeta1 mediated growth inhibition, suggesting TGFbeta1 participation in the development of these cancers. The tumor suppressor gene DPC4/SMAD4, which is frequently inactivated in carcinoma cells, has been described as a key player in TGFbeta1 mediated growth inhibition. However, some carcinoma cells lacking functional SMAD4 are sensitive to TGFbeta1 induced growth inhibition, thus requiring a SMAD4 independent TGFbeta1 pathway.

Results: Here we report that mature TGFbeta1 is a ligand for the integrin alphaVbeta6, independent of the common integrin binding sequence motif RGD. After TGFbeta1 binds to alphaVbeta6 integrin, different signaling proteins are activated in TGFbeta1-sensitive carcinoma cells, but not in cells that are insensitive to TGFbeta1. Among others, interaction of TGFbeta1 with the alphaVbeta6 integrin resulted in an upregulation of the cell cycle inhibitors p21/WAF1 and p27 leading to growth inhibition in SMAD4 deleted as well as in SMAD4 wildtype carcinoma cells.

Conclusions: Our data provide support for the existence of an alternate TGFbeta1 signaling pathway that is independent of the known SMAD pathway. This alternate pathway involves alphaVbeta6 integrin and the Ras/MAP kinase pathway and does not employ an RGD motif in TGFbeta1-sensitive tumor cells. The combined action of these two pathways seems to be necessary to elicit a complete TGFbeta1 signal.

Show MeSH
Related in: MedlinePlus