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DPC4/SMAD4 mediated tumor suppression of colon carcinoma cells is associated with reduced urokinase expression
I Schwarte-Waldhoff1, S Klein, S Blass-Kampmann
1Medizinische Universitätsklinik, Knappschaftskrankenhaus, Ruhr-Universität Bochum, Germany.
Abstract:
We recently identified DPC4/Smad4 as a candidate tumor suppressor gene mutated or lost in one half of pancreatic carcinomas and in a subset of colon and biliary tract carcinomas. DPC4 plays a key role in signal transduction of the TGF-beta superfamily of molecules and inactivation of TGF-beta mediated growth inhibition is supposed to be the driving force for DPC4 inactivation in human tumors. However, DPC4 mediated tumor suppression by reconstitution of defective cells has not yet been reported. Here we show suppression of tumorigenicity in nude mice by stable reexpression of DPC4 in SW480 colon carcinoma cells. In vitro growth of DPC4-transfected cells was not affected and resistance towards TGF-beta mediated growth inhibition was retained. Instead, cells exhibited morphological alterations and adhesion and spreading were accelerated. These phenotypic changes were associated with reduced expression levels of the endogenous urokinase-type plasminogen activator (uPA) and plasminogen-activator-inhibitor-1 (PAI-1) genes, the products of which are implicated in the control of cell adhesion and invasion. In patients, high expression levels of uPA and PAI-1 correlate with poor prognosis. Thus, reduced expression of uPA and PAI-1 is consistent with suppression of tumorigenicity in DPC4 reconstituted cells. These results demonstrate DPC4's tumor suppressive function and suggest a potential role for DPC4 as a modulator of cell adhesion and invasion.
Insights
Restoring the DPC4/Smad4 gene suppressed colon cancer growth in mice. This tumor suppressor gene also reduced cell invasion by lowering urokinase-type plasminogen activator (uPA) and PAI-1 expression.
Area of Science:
- Molecular Biology
- Oncology
- Cell Biology
Background:
- DPC4/Smad4 is a candidate tumor suppressor gene frequently lost in pancreatic, colon, and biliary tract carcinomas.
- DPC4/Smad4 is crucial for TGF-beta signaling, and its inactivation is linked to tumor development by abrogating TGF-beta-mediated growth inhibition.
Purpose of the Study:
- To investigate the tumor suppressive function of DPC4/Smad4 through gene reconstitution in cancer cells.
- To determine the impact of DPC4/Smad4 reexpression on colon carcinoma cell behavior and tumorigenicity.
Main Methods:
- Stable reexpression of DPC4/Smad4 in SW480 colon carcinoma cells.
- Assessment of in vitro cell growth, TGF-beta response, morphology, adhesion, and spreading.
- Analysis of endogenous urokinase-type plasminogen activator (uPA) and plasminogen-activator-inhibitor-1 (PAI-1) gene expression levels.
Main Results:
- Stable DPC4/Smad4 reexpression suppressed tumorigenicity of colon carcinoma cells in nude mice.
- In vitro growth was unaffected, but TGF-beta-mediated growth inhibition resistance was retained.
- Phenotypic changes included altered cell morphology, accelerated adhesion and spreading, and reduced uPA and PAI-1 expression.
Conclusions:
- DPC4/Smad4 exhibits a tumor suppressive function, independent of TGF-beta-mediated growth inhibition.
- Reduced expression of uPA and PAI-1 is associated with DPC4/Smad4-mediated suppression of tumorigenicity.
- DPC4/Smad4 may play a role in modulating cell adhesion and invasion, offering potential therapeutic targets.