Smad7 mediates apoptosis induced by transforming growth factor β in prostatic carcinoma cells (original) (raw)
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Cancer Research, 2009
Transforming growth factor-B (TGF-B) functions as a tumor suppressor of the prostate through mechanisms that remain unresolved. Although TGF-B receptors directly activate both Smads 2 and 3, to date, Smad3 has been shown to be the essential mediator of most Smad-dependent TGF-B responses, including control of gene expression, cell growth, apoptosis, and tumor suppression. Using a robust lentiviral short hairpin RNA system to silence Smads 2 and/or 3 in the NRP-152 nontumorigenic rat prostate basal epithelial cell line, we provide the first evidence for Smad2 as a critical mediator of TGF-B-induced apoptosis and gene expression. Parallel analyses revealed that Smad3 is the major mediator of TGF-B-induced transcriptional and apoptotic responses in the NRP-154 rat prostate carcinoma cell line. Remarkably, silencing Smad2 alone caused malignant transformation of NRP-152 cells, as assayed by s.c. tumor growth in athymic mice, whereas silencing Smad3 alone did not induce tumors. Nevertheless, tumors induced by silencing both Smads 2 and 3 were larger than those from silencing Smad2 alone. Given previous reports that NRP-152 cells have a stem cell phenotype, we speculate a critical role for Smad2 as a tumor suppressor in the basal epithelial or stem cell compartment of the prostate.
Altered levels of Smad2 and Smad4 are associated with human prostate carcinogenesis
Prostate Cancer and Prostatic Diseases, 2006
Alterations have been demonstrated in ligand and cognate receptor system of the transforming growth factor beta (TGF-b) pathway in prostate cancer (PC). Still, little is known about changes in the activity of the intracellular Smad cascade of TGF-b signaling during prostate carcinogenesis. We used immunohistochemistry to analyze phosphorylated Smad2 (p-Smad2), nuclear Smad4 and inhibitory-Smad7 in epithelial cells of normal, hyperplastic and malignant prostate. Specimens comprised 49 tissue cores of PC, 10 benign prostate hypertrophies and three normal prostates. Nuclear p-Smad2 (Po0.001) and nuclear Smad4 (P ¼ 0.023) were significantly decreased in PC with remarkable variations in cytoplasmic Smad7 levels. Substantial decreases in p-Smad2 and Smad4 levels were found in specimens with primary Gleason grades 3 and 4, whereas in grade 5, levels were markedly higher. Our results provide the first evidence for changes and reversible attenuation in the Smad system of the TGF-b pathway during prostate carcinogenesis.
Journal of Biological Chemistry, 2001
Smad proteins are major components in the intracellular signaling pathway of transforming growth factor- (TGF-), and phosphorylation is an important mechanism in regulation of their functions. Smad7 was identified as a potent inhibitor of TGF--dependent signaling. We have identified serine 249 in Smad7 as a major phosphorylation site, the phosphorylation of which was not affected by TGF-1. Abrogation of the phosphorylation by substitution of Ser-249 with alanine or aspartic acid residues did not affect the ability of Smad7 to inhibit TGF-1 and BMP7 signaling. No differences were found in the stability or in the intracellular distribution of Smad7 mutants compared with the wild-type molecule. However, Smad7 fused to the DNA-binding domain of GAL4 induced transcription from a reporter with mutated TATA minimal promoter in a Ser-249-dependent manner. Moreover, a reporter with the SV40 minimal promoter was inhibited by GAL4-Smad7, and this effect was also dependent on Ser-249 phosphorylation. The amplitude of effects on transcriptional regulation was dependent on cell type. Our results suggest that phosphorylation of Smad7, unlike phosphorylation of the receptor-regulated Smads, does not regulate TGF- signaling but rather affects TGF--independent effects of Smad7 on transcriptional regulation.
Evidence for a Role of Smad3 and Smad2 in Stabilization of the Tumor-derived Mutant Smad2.Q407R
Journal of Biological Chemistry, 2003
Transforming growth factor  (TGF-) is a potent inhibitor of cell proliferation and the loss of responsiveness to TGF- may contribute to the development of human cancers. In hepatocellular carcinomas, the potential role of TGF- signaling as a tumor suppressor pathway can be illustrated by the presence of mutations in genes encoding TGF- receptors or downstream components of this signaling such as Smad2. Although Smad2 is mutated in hepatocellular carcinomas, the alteration of TGF- signaling with respect to tumor progression remains to be established. Using the HepG2 hepatoma cells, we showed here that expression of Smad2.Q407R, a missense mutation found in human hepatocellular carcinoma, was less effective than expression of wild-type Smad2 in enhancing the ability of TGF- to induce transcription from the Mix.2 promoter. This effect was specifically associated with a decrease in the steady-state level of Smad2.Q407R, presumably because of an enhancement of its ubiquitination and degradation through the proteasome machinery. More importantly, we found that the unstability of Smad2.Q407R was reversed when this mutant undergoes homo-oligomerization with wild-type Smad2 or hetero-oligomerization with Smad3 within the cells. Therefore, our findings allowed us to propose a novel mechanism for suppression of the deleterious effect of a tumor-derived mutation of Smad2, which loss may lead to dysregulated cell proliferation during tumorigenesis. Transforming growth factor- (TGF-) 1 regulates a broad range of cellular functions (1), including cell cycle arrest, regulation of extracellular matrix production, and induction of programmed cell death. TGF- signals through a heteromeric complex of two types of transmembrane serine/threonine kinases, the type I (TRI) and type II (TRII) receptors. TGF- binding to TRII induces recruitment and phosphorylation of TRI that transduces signals to downstream intracellular substrates, the Smad proteins (2, 3). The interaction of receptor complex and receptor-regulated Smads (R-Smad), Smad2 and Smad3, is facilitated by SARA (Smad anchor for receptor acti
The Dual Role of Smad7 in the Control of Cancer Growth and Metastasis
International Journal of Molecular Sciences, 2013
Smad7 was initially identified as an inhibitor of Transforming growth factor (TGF)-β due mainly to its ability to bind TGF-β receptor type I and prevent TGF-β-associated Smad signaling. More recently, it has been demonstrated that Smad7 can interact with other intracellular proteins and regulate also TGF-β-independent signaling pathways thus making a valid contribution to the neoplastic processes in various organs. In particular, data emerging from experimental studies indicate that Smad7 may differently modulate the course of various tumors depending on the context analyzed. These observations, together with the demonstration that Smad7 expression is deregulated in many cancers, suggest that therapeutic interventions around Smad7 can help interfere with the development/progression of human cancers. In this article we review and discuss the available data supporting the role of Smad7 in the modulation of cancer growth and progression.
Signaling of transforming growth factor-β family members through Smad proteins
European Journal of Biochemistry, 2000
Smads are pivotal intracellular nuclear effectors of transforming growth factor-b (TGF-b) family members. Ligand-induced activation of TGF-b family receptors with intrinsic serine/threonine kinase activity trigger phosphorylation of receptor-regulated Smads (R-Smads), whereas Smad2 and Smad3 are phosphorylated by TGF-b, and activin type I receptors, Smad1, Smad5 and Smad8, act downstream of BMP type I receptors. Activated R-Smads form heteromeric complexes with common-partner Smads (Co-Smads), e.g. Smad4, which translocate efficiently to the nucleus, where they regulate, in co-operation with other transcription factors, coactivators and corepressors, the transcription of target genes. Inhibitory Smads act in most cases in an opposite manner from R-and Co-Smads. Like other components in the TGF-b family signaling cascade, Smad activity is intricately regulated. The multifunctional and context dependency of TGF-b family responses are reflected in the function of Smads as signal integrators. Certain Smads are somatically mutated at high frequency in particular types of human cancers. Gene ablation of Smads in the mouse has revealed their critical roles during embryonic development. Here we review the latest advances in our understanding of the Smad mechanism of action and their in vivo functions.