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Smad4 dependency defines two classes of transforming growth factor {beta} (TGF-{beta}) target genes and distinguishes TGF-{beta}-induced epithelial-mesenchymal transition from its antiproliferative and migratory responses.

ABSTRACT: In response to transforming growth factor beta (TGF-beta), Smad4 forms complexes with activated Smad2 and Smad3, which accumulate in the nucleus, where they both positively and negatively regulate TGF-beta target genes. Mutation or deletion of Smad4 is found in about 50% of pancreatic tumors and in about 15% of colorectal tumors. As Smad4 is a central component of the TGF-beta/Smad pathway, we have determined whether Smad4 is absolutely required for all TGF-beta responses, to evaluate the effect of its loss during human tumor development. We have generated cell lines from the immortalized human keratinocyte cell line HaCaT or the pancreatic tumor cell line Colo-357, which stably express a tetracyline-inducible small interfering RNA targeted against Smad4. In response to tetracycline, Smad4 expression is effectively silenced. Large-scale microarray analysis identifies two populations of TGF-beta target genes that are distinguished by their dependency on Smad4. Some genes absolutely require Smad4 for their regulation, while others do not. Functional analysis also indicates a differential Smad4 requirement for TGF-beta-induced functions; TGF-beta-induced cell cycle arrest and migration, but not epithelial-mesenchymal transition, are abolished after silencing of Smad4. Altogether our results suggest that loss of Smad4 might promote TGF-beta-mediated tumorigenesis by abolishing tumor-suppressive functions of TGF-beta while maintaining some tumor-promoting TGF-beta responses.

SUBMITTER: Levy L

PROVIDER: S-EPMC1234333 | biostudies-literature | 2005 Sep

REPOSITORIES: biostudies-literature

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Smad4 dependency defines two classes of transforming growth factor {beta} (TGF-{beta}) target genes and distinguishes TGF-{beta}-induced epithelial-mesenchymal transition from its antiproliferative and migratory responses.

Levy Laurence L Hill Caroline S CS

Molecular and cellular biology 20050901 18

In response to transforming growth factor beta (TGF-beta), Smad4 forms complexes with activated Smad2 and Smad3, which accumulate in the nucleus, where they both positively and negatively regulate TGF-beta target genes. Mutation or deletion of Smad4 is found in about 50% of pancreatic tumors and in about 15% of colorectal tumors. As Smad4 is a central component of the TGF-beta/Smad pathway, we have determined whether Smad4 is absolutely required for all TGF-beta responses, to evaluate the effect ...[more]

PMID: 16135802

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Project description:Appropriate growth and development of the endometrium across the menstrual cycle is key for a woman's quality of life and reproductive well-being. Recurrent pregnancy loss (RPL) and heavy menstrual bleeding (HMB) affect a significant proportion of the female population worldwide. These endometrial pathologies have a significant impact on a woman's quality of life as well as placing a high economic burden on a country's health service. An underlying cause for both conditions is unknown in approximately 50% of cases. Previous research has demonstrated that aberrant endometrial vascular maturation is associated with both RPL and HMB, where it is increased in RPL but reduced in HMB. TGFβ1 is one of the key growth factors that regulate vascular maturation, by inducing phenotypic switching of vascular smooth muscle cells (VSMCs) from a synthetic phenotype to a more contractile one. Our previous data demonstrated an increase in TGFβ1 in the endometrium of RPL, while others have shown a decrease in women with HMB. However, TGFβ1 bioavailability is tightly controlled, and we therefore sought to perform an extensive immunohistochemical analysis of different components in the pathway in the endometrium of normal controls, women with HMB or RPL. In addition, two in vitro models were used to examine the role of TGFβ1 in endometrial vascular maturation and endothelial cell (EC):VSMC association. Taken all together, the immunohistochemical data suggest a decrease in bioavailability, receptor binding capacity, and signaling in the endometrium of women with HMB compared with controls. In contrast, there is an increase in the bioavailability of active TGFβ1 in the endometrium of women with RPL compared with controls. Endometrial explants cultured in TGFβ1 had an increase in the number of vessels associated with contractile VSMC markers, although the total number of vessels did not increase. In addition, TGFβ1 increased EC:VSMC association in an in vitro model. In conclusion, TGFβ1 is a key regulator of endometrial vascular maturation and could be considered as a therapeutic target for women suffering from HMB and/or RPL.

Project description:Background and aimsTransforming growth factor beta (TGF-beta) is frequently involved in gastrointestinal carcinogenesis although its contribution to oesophageal adenocarcinoma (AC) and its precursor Barrett's oesophageal epithelium (BE) metaplasia are unclear.MethodsExpression of TGF-beta signalling components was assessed by reverse transcription-polymerase chain reaction (PCR), western blot, and immunohistochemistry in oesophageal endoscopic biopsies and cell lines. Genomic alterations in SMAD4 were characterised by fluorescence in situ hybridisation, methylation specific PCR, and sequencing. Functional integrity of TGF-beta signalling was assessed by characterisation of p21 and proliferation status. Smad4 negative BIC-1 cells were transiently transfected with smad4 and TGF-beta responsiveness evaluated.Resultssmad4 mRNA expression was progressively reduced in the metaplasia-dysplasia-adenocarcinoma sequence (p<0.01). A quarter of AC samples displayed an abnormal Smad4 protein isoform, with no corresponding changes in gene sequence or organisation. Methylation of smad4 has not been described previously but we found promoter methylation in 70% of primary AC samples. In 6/8 oesophageal cell lines, chromosomal rearrangements affected the smad4 locus. Lack of smad4 expression in BIC-1 cells occurred secondary to loss of one copy and extensive deletion of the second allele's promoter region. TGF-beta dependent induction of p21 and downregulation of minichromosome maintenance protein 2 was lost in >80% of BE and AC. TGF-beta failed to inhibit proliferation in 5/8 oesophageal cell lines. In BIC-1, the antiproliferative response was restored following transient transfection of smad4 cDNA.ConclusionsIn BE carcinogenesis, downregulation of Smad4 occurs due to several different mechanisms, including methylation, deletion, and protein modification. Frequent alterations in TGF-beta signalling lead to a functionally significant impairment of TGF-beta mediated growth suppression.

Dataset Information

Smad4 dependency defines two classes of transforming growth factor {beta} (TGF-{beta}) target genes and distinguishes TGF-{beta}-induced epithelial-mesenchymal transition from its antiproliferative and migratory responses.

Publications

Smad4 dependency defines two classes of transforming growth factor {beta} (TGF-{beta}) target genes and distinguishes TGF-{beta}-induced epithelial-mesenchymal transition from its antiproliferative and migratory responses.

Similar Datasets

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