Disease relevance of Smad4

• Taking advantage of this fact, we constructed previously a cis-compound Apc(delta716) Smad4 mutant, the intestinal polyps of which progress to very invasive adenocarcinomas [1].
• In both simple Apc(Delta716) and compound Apc(Delta716) Smad4 mutants, MVD increased in a polyp size-dependent manner only in the polyps expanded beyond a threshold of about 1 mm in diameter [2].
• Thus, the phenotypes of breast tumors in vivo paralleled that of human breast cancer cell lines in terms of Smad2P and Smad4 expression [3].
• Loss of Smad4 was inversely correlated with the presence of axillary lymph node metastases [3].
• We recently inactivated its mouse homologue Smad4 and demonstrated its role in the malignant progression of benign adenomas to invasive adenocarcinomas by analyzing mice with Apc and Smad4 compound mutations [4].

High impact information on Smad4

• Using cis-Apc(+/Delta716) Smad4(+/-) mutant mice (referred to as cis-Apc/Smad4), a model of invasive colorectal cancer in which TGF-beta family signaling is blocked, we show here that a new type of immature myeloid cell (iMC) is recruited from the bone marrow to the tumor invasion front [5].
• In humans, mutations in BMPR1A, SMAD4 and PTEN are responsible for juvenile polyposis syndrome, juvenile intestinal polyposis and Cowden disease, respectively [6].
• Smads 1, 2, 3, 5 and 8 are activated upon phosphorylation by specific type I receptors, and associate with the common partner Smad4 to trigger transcriptional responses [7].
• Because both Apc and Dpc4 are located on chromosome 18, we constructed compound heterozygotes carrying both mutations on the same chromosome by meiotic recombination [8].
• The DPC4 (SMAD4) gene plays a key role in the TGFbeta signaling pathway [8].

Biological context of Smad4

• By PCR genotyping and immunohistochemical staining, the wild-type Smad4 allele has been lost in the polyp epithelial cells, ie., loss of heterozygosity [4].
• Although simple Smad4 homozygotes were embryonically lethal, the heterozygotes were fertile and appeared normal up to the age of 1 year [4].
• The tumor suppressor gene Smad4 has been proposed to be a common mediator of transforming growth factor beta (TGFbeta)-related signaling pathways [9].
• Because both Apc and Smad4 are located on mouse chromosome 18, we constructed by meiotic recombination compound heterozygotes carrying both mutations on the same chromosome [10].
• Smad4 and GATA4 were also found to bind in vivo with the Nkx2-5 composite enhancer, as revealed by chromatin immunoprecipitation analysis of differentiated P19 cells [11].

Anatomical context of Smad4

• Moreover, only one of the cell lines failed to express Smad4 [3].
• Moreover, reporter assays of the Msx-2 promoter revealed an absolute requirement for Smad4 in fibroblasts and ES cells for activation [9].
• These alterations are initiated by a dramatic expansion of the gastric epithelium where Smad4 is expressed [12].
• These studies demonstrate that Smad4 functions as a tumor suppressor in the gastrointestinal tract and also provide a valuable model for screening factors that promote or prevent gastric tumorigenesis [12].
• Here we show that Smad4+/- mice began to develop polyposis in the fundus and antrum when they were over 6 - 12 months old, and in the duodenum and cecum in older animals at a lower frequency [12].

Associations of Smad4 with chemical compounds

• Gastro-intestinal tumorigenesis in Smad4 mutant mice [10].
• During pre-implantation period, Smad2 hybridization signals were accumulated in the luminal and glandular epithelium at a basal level; Smad4 mRNA appeared in the epithelium with a little variation in hybridization signal intensity [13].
• In amifostine-treated marrows, smad 2/3 and smad4 were not detected in the nucleus but were positive in the cytoplasm of megakaryocytes 10 days after irradiation [14].
• Here we show that sphingosine 1-phosphate, independently of transforming growth factor beta secretion, induces a rapid phosphorylation of Smad3 on its C-terminal serine motif and induces its partnering with Smad4 and the translocation of the complex into the nucleus [15].
• Regulation of steroidogenesis is disrupted in the Smad4 conditional knockout, leading to increased levels of serum progesterone [16].

Physical interactions of Smad4

• A transforming growth factor beta-induced Smad3/Smad4 complex directly activates protein kinase A [17].

Regulatory relationships of Smad4

• Smad4 mutant also inhibited the up-regulation of surface beta(5) level by TGF-beta [18].
• Moreover, complete loss of Smad4 strongly enhances Apc-driven tumor formation [19].

Other interactions of Smad4

• Moreover, Smad2 or Smad3 with Smad4 enhanced the proteolytic pathway of p57(Kip2) [20].
• After implantation, on day 5 of pregnancy, Smad2 signals were localized to the subluminal stroma surrounding the implanting blastocyst, and Smad4 mRNA were accumulated in the decidua near the luminal epithelium [13].
• By deletion and mutational analyses we localized a Smad1/Smad4-binding site containing a GCAT motif, which showed similarity to other TGF-beta family responsive elements [21].
• To assess the involvement of intracellular signaling protein Smads in regulating goldfish FSHbeta promoter, we first cloned full-length cDNAs for goldfish Smad2, Smad3, Smad4, and Smad7 from the pituitary [22].
• Indeed, Nkx3.2 both fails to associate with the HDAC/Sin3A complex and represses target gene transcription in a cell line lacking Smad4, but it performs these functions if exogenous Smad4 is added to these cells [23].
• These studies demonstrate essential roles of Smad4-mediated TGFbeta signaling in coupling bone formation and bone resorption and maintaining normal postnatal bone homeostasis [24].

Analytical, diagnostic and therapeutic context of Smad4

• RT-PCR results showed that both Smad2 and Smad4 mRNA levels were rising during peri-implantatation [13].
• In situ hybridization and semi-quantitative RT-PCR were employed to determine the temporal and spatial expression of Smad2 and Smad4 mRNA in mouse uterus during the oestrous cycle and early pregnancy [13].
• These lesions share histological features of gastric polyps in aging mice with monoallelic null mutations in Smad4, which encodes the common transducer for transforming growth factor (TGF)-beta signaling [25].
• Here, we show by loss of heterozygosity (LOH) analysis and immunohistochemistry (IHC) that, although the majority of the tumors appear at 9 months of age, somatic loss of the wild-type Smad4 allele occurs only at later stages of tumor progression [19].
• RESULTS: We demonstrate that expression of Smad4/DPC4 in Capan-1 cells reduced anchorage-independent growth by more than 50%, and inhibited xenograft tumor growth [26].

References