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Increased smad expression and activation are associated with apoptosis in normal and malignant prostate after
G Brodin1, P ten Dijke, K Funa
1Ludwig Institute for Cancer Research, Biomedical Center, Uppsala, Sweden.
Abstract:
Transforming growth factor (TGF)-beta1 is induced in the prostate after castration and has been implicated in apoptosis of epithelial cells during involution. TGF-beta1-mediated receptor activation induces phosphorylation of Smad2 and Smad3, which form complexes with Smad4, that translocate to the nucleus to regulate transcription of target genes. Smad6 and Smad7 antagonize the action of signal-transducing Smads. We have examined the immunohistochemical expression of different Smad molecules in the epithelium of rat ventral prostate before and after castration, in androgen-sensitive Dunning R3327 PAP prostatic tumor cells from untreated and castrated rats, and after treatment with estrogen. In the ventral prostate, a significant increase of phosphorylated Smad2 (P-Smad2) was observed after castration. In prostatic tumor cells we observed an increased expression of Smad2 and P-Smad2 after treatment. The levels of Smad3 and, in particular, Smad4 were enhanced in the normal ventral prostate, as well as in the tumors after castration. Interestingly, Smad6 and Smad7 expression was also up-regulated in cells with increased Smad2 activation. The staining for Smad2, P-Smad2, Smad3, Smad4, and Smad7 was nuclear in some cells and was present in areas with a large number of apoptotic cells identified by various morphological criteria, formation of apoptotic bodies and, in adjacent sections, by terminal deoxynucleotidyl transferase-mediated nick end labeling assay. Our results suggest that the signal transduction pathway for TGF-beta, leading to apoptosis, is activated in the normal prostate after castration and in the tumor model after castration, without or with estrogen treatment.
Insights
Castration activates the transforming growth factor (TGF)-beta signaling pathway in the prostate, leading to increased cell death (apoptosis) in both normal and cancerous tissues. This pathway involves Smad proteins and is crucial for prostate involution and tumor response.
Area of Science:
- Cell Biology
- Molecular Biology
- Oncology
Background:
- Transforming growth factor (TGF)-beta1 is induced post-castration and linked to prostate epithelial cell apoptosis during involution.
- TGF-beta1 signaling involves Smad2/3 phosphorylation, Smad4 complex formation, and nuclear translocation to regulate gene transcription.
- Smad6 and Smad7 act as antagonists to the signal-transducing Smads.
Purpose of the Study:
- To investigate the immunohistochemical expression of Smad molecules in rat ventral prostate and Dunning R3327 PAP prostatic tumor cells.
- To analyze Smad expression changes before and after castration, and in response to estrogen treatment in tumor cells.
- To correlate Smad expression with apoptosis in prostate tissues and tumors.
Main Methods:
- Immunohistochemical analysis of Smad2, phosphorylated Smad2 (P-Smad2), Smad3, Smad4, Smad6, and Smad7 expression.
- Examination of rat ventral prostate and Dunning R3327 PAP prostatic tumor cells.
- Assessment of apoptosis using morphological criteria and terminal deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) assay.
Main Results:
- Castration significantly increased P-Smad2 in the ventral prostate.
- Prostatic tumor cells showed increased Smad2 and P-Smad2 expression after treatment.
- Smad3, Smad4, Smad6, and Smad7 levels were elevated in the normal prostate and tumors post-castration, correlating with increased Smad2 activation and apoptotic areas.
Conclusions:
- The TGF-beta signal transduction pathway, leading to apoptosis, is activated in the normal prostate following castration.
- This pathway is also activated in the Dunning R3327 PAP prostate tumor model after castration, irrespective of estrogen treatment.
- Smad6 and Smad7 expression is upregulated in response to increased Smad2 activation, suggesting a regulatory feedback mechanism.