In the past two decades, multiple studies have revealed that SMAD4 loss on its own does not initiate tumor formation, but can promote tumor progression initiated by other genes, such as KRAS activation in pancreatic duct adenocarcinoma and APC inactivation in colorectal cancer.
The frequency of genomic alterations seen in SBA demonstrated distinct differences in comparison with either colorectal cancer (APC: 26.8% [85 of 317] vs 75.9% [4823 of 6353], P < .001; and CDKN2A: 14.5% [46 of 317] vs 2.6% [165 of 6353], P < .001) or gastric carcinoma (KRAS: 53.6% [170 of 317] vs 14.2% [126 of 889], P < .001; APC: 26.8% [85 of 317] vs 7.8% [69 of 889], P < .001; and SMAD4: 17.4% [55 of 317] vs 5.2% [46 of 889], P < .001).
Obtained results, though preliminary, also indicate that SMAD4 gene promoter haplotype -462T(14)/-4T(10) may represent a genetic marker of potential relevance for pancreatic and colorectal cancer.
In conclusion, Smad4 could be considered as a central component of EMT transition in human colorectal cancer that combines with transcriptional factors to reduce E-cadherin and alter the expression of the epithelial phenotype.
Although Smad4 is regarded as a signaling mediator of the TGFβ signaling pathway, its role as a major suppressor of colorectal cancer progression and the molecular events underlying this phenomenon remain elusive.
SMAD4 is a gastrointestinal malignancy-specific tumor suppressor gene found mutated in one third of colorectal cancer specimens and half of pancreatic tumors.
Loss of Smad4 protein expression and 18qLOH as molecular markers indicating lymph node metastasis in colorectal cancer--a study matched for tumor depth and pathology.
However, thus far few studies have analyzed the impact of numerical abnormalities of chromosomes 17 and 18, which carry the p53 and DCC plus SHAD4/DPC4 genes involved in colorectal cancer, on the clinical and biological behaviors of the disease.
Significantly, miR-4260 was increased in human colorectal cancer tissues with simultaneous downregulation of MCC and SMAD4, strongly suggesting the clinical relevance of targeting miR-4260 in the treatment of colorectal cancer.
To address whether Smad4 was required for enhancing metastatic potentials by BMP-4 in colorectal cancer, we generated BMP-4 overexpressing clones from Smad4-deficient SW480 cells.
Utilising a recently developed method of immunohistochemical staining for Smad4 protein, we focused on the specific impact of Smad4 protein expression on liver metastasis in colorectal cancer.
Our data show SMAD4 loss correlates with worse clinical outcome, resistance to chemotherapy, and decreased immune infiltrate, supporting its use as a prognostic marker in patients with colorectal cancer.
In human clinical specimens, we found that neutrophil infiltration into the peritumoral stroma was more marked in SMAD4-negative colorectal cancer compared with that in SMAD4-positive colorectal cancer, and that both CXCL1 and CXCL8 were abundantly expressed in the tumor-infiltrating neutrophils.
Two missense mutations in the C-terminal domain of Smad4, D351H (Asp351-->His) and D537Y (Asp537-->Tyr), have been described recently in the human colorectal cancer cell lines CACO-2 and SW948 respectively [Woodford-Richens, Rowan, Gorman, Halford, Bicknell, Wasan, Roylance, Bodmer and Tomlinson (2001) Proc.Natl.Acad.Sci.U.S.A. 98, 9719-9723].