A novel link between the proteasome pathway and the signal transduction pathway of the Bone Morphogenetic Proteins (BMPs)

BACKGROUND: The intracellular signaling events of the Bone Morphogenetic Proteins (BMPs) involve the R-Smad family members Smad1, Smad5, Smad8 and the Co-Smad, Smad4. Smads are currently considered to be DNA-binding transcriptional modulators and shown to recruit the master transcriptional co-activator CBP/p300 for transcriptional activation. SNIP1 is a recently discovered novel repressor of CBP/p300. Currently, the detailed molecular mechanisms that allow R-Smads and Co-Smad to co-operatively modulate transcription events are not fully understood. RESULTS: Here we report a novel physical and functional link between Smad1 and the 26S proteasome that contributes to Smad1- and Smad4-mediated transcriptional regulation. Smad1 forms a complex with a proteasome β subunit HsN3 and the ornithine decarboxylase antizyme (Az). The interaction is enhanced upon BMP type I receptor activation and occur prior to the incorporation of HsN3 into the mature 20S proteasome. Furthermore, BMPs trigger the translocation of Smad1, HsN3 and Az into the nucleus, where the novel CBP/p300 repressor protein SNIP1 is further recruited to Smad1/HsN3/Az complex and degraded in a Smad1-, Smad4- and Az-dependent fashion. The degradation of the CBP/p300 repressor SNIP1 is likely an essential step for Smad1-, Smad4-mediated transcriptional activation, since increased SNIP1 expression inhibits BMP-induced gene responses. CONCLUSIONS: Our studies thus add two additional important functional partners of Smad1 into the signaling web of BMPs and also suggest a novel mechanism for Smad1 and Smad4 to co-modulate transcription via regulating proteasomal degradation of CBP/p300 repressor SNIP1

Transforming growth factor-beta receptor III downregulation in prostate cancer: is inhibin B a tumor suppressor in prostate?

The transforming growth factor-beta (TGF-beta) pathway plays dual roles in cancer, inhibiting epithelial cell growth under normal physiologic conditions, but promoting invasion and metastasis once growth inhibitory responses are lost. Two recent papers show that TGF-beta receptor III is the most common TGF-beta pathway component downregulated in prostate cancer. Here, we discuss the implications of these findings and what it may mean about the biology of this disease

Transforming Growth Factor-β1 Effects on Endothelial Monolayer Permeability Involve Focal Adhesion Kinase/Src

Transforming growth factor (TGF)-β1 activity has been shown to increase vascular endothelial barrier permeability, which is believed to precede several pathologic conditions, including pulmonary edema and vessel inflammation. In endothelial monolayers, TGF-β1 increases permeability, and a number of studies have demonstrated the alteration of cell–cell contacts by TGF-β1. We hypothesized that focal adhesion complexes also likely contribute to alterations in endothelial permeability. We examined early signal transduction events associated with rapid changes in monolayer permeability and the focal adhesion complex of bovine pulmonary artery endothelial cells. Western blotting revealed rapid tyrosine phosphorylation of focal adhesion kinase (FAK) and Src kinase in response to TGF-β1; inhibition of both of these kinases using pp2 (4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine), ameliorates TGF-β1–induced monolayer permeability. Activation of FAK/Src requires activation of the epidermal growth factor receptor downstream of the TGF-β receptors, and is blocked by the epidermal growth factor receptor inhibitor AG1478. Immunohistochemistry showed that actin and the focal adhesion proteins paxillin, vinculin, and hydrogen peroxide–inducible clone-5 (Hic-5) are rearranged in response to TGF-β1; these proteins are released from focal adhesion complexes. Rearrangement of paxillin and vinculin by TGF-β1 is not blocked by the FAK/Src inhibitor, pp2, or by SB431542 inhibition of the TGF-β type I receptor, anaplastic lymphoma kinase 5; however, pp1 (4-Amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine), which inhibits both type I and type II TGF-β receptors, does block paxillin and vinculin rearrangement. Hic-5 protein rearrangement requires FAK/Src activity. Together, these results suggest that TGF-β1–induced monolayer permeability involves focal adhesion and cytoskeletal rearrangement through both FAK/Src-dependent and -independent pathways

Conditional knockout of theSmad1 gene

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Circulating tumor cells: application as a biomarker for molecular characterization and predictor of survival in an all-comer solid tumor phase I clinical study.

Clinical development of cancer drugs has a low success rate. Prognostic and predictive biomarkers using minimally invasive approaches hold promise for increasing the probability of success by enabling disease characterization, patient selection and early detection of drug treatment effect. Enumeration and molecular characterization of circulating tumor cells (CTC) may address some of these needs, and thus were evaluated for utility in a Phase I solid tumor clinical study.Blood samples for CTC analysis were obtained from 24 cancer patients in a multi-center all-comer Phase I study of MEDI-575, a novel anti-PDGFRα antibody. Samples were taken at screening and analyzed for enumeration of CTC using the CellSearch(®) platform and for molecular characterization using a novel quantitative RT-PCR assay.Fifty-nine percent of the patients showed at least 1 CTC per 7.5 ml of blood at baseline. Progression-free survival (PFS) and overall survival (OS) of patients with 0 CTCs at baseline were longer than PFS and Os for patients with 1-3 and >3 CTCs (8.8 versus 1.4 and 1.3 months PFS, P = 0.02; 9.0 vs 7.4 and 3.5 months OS, P = 0.20, respectively). Patients with 0 CTC showed a greater percentage of stable disease than the other 2 groups with 1-3 and >3 CTCs (57% vs 29% and 0%). The multimarker qRT-PCR method detected CTC in 40% of the patients, and 80% of these patients were positive for pre-selected drug target genes.CTC enumeration of patients in an all-comer study is feasible and may allow for patient stratification for PFS and Os to evaluate the clinical response of investigational agents. Gene expression profiling of isolated CTC may provide a means for molecular characterization of selected tumor targets