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Alterations of Smad signaling in human breast carcinoma are associated with poor outcome: a tissue microarray study
Wen Xie1, Joachim C Mertens, Daniel J Reiss
1Division of Medical Oncology, Department of Internal Medicine, The Cancer Institute of New Jersey, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, New Brunswick, New Jersey 08903, USA.
Abstract:
Based largely on studies of cell lines in vitro and of transgenic mouse models, disruptions of transforming growth factor (TGF) beta signaling are thought to contribute to the development and progression of human breast cancer. However, whether and how TGF-beta signaling becomes disrupted during human breast cancer development in vivo remains largely unknown. To address this question, we have compared the patterns of expression and activation of the postreceptor components of the TGF-beta signaling pathway, the so-called Smads, in human breast cancer cell lines with those in breast carcinoma specimens. None of the breast carcinoma cell lines were growth arrested by TGF-beta in vitro. Each of the tumor cell lines expressed normal levels of Smad2 and -3. Moreover, TGF-beta treatment induced phosphorylation of Smad2 (Smad2P) in each of these lines, except those that lacked TGF-beta type II receptors. Moreover, only one of the cell lines failed to express Smad4. Among 456 cases of human breast carcinoma assembled in tissue microarrays, the majority (92%) expressed Smad2, Smad2P, as well as Smad4, indicating their ability to proliferate within a microenvironment that contains bioactive TGF-beta. Thirty cases (6.6%) failed to express Smad2P, suggesting the loss of TGF-beta receptor signaling. Nine cases (2%) failed to express Smad4, and 3 of these also failed to express Smad2P. Thus, the phenotypes of breast tumors in vivo paralleled that of human breast cancer cell lines in terms of Smad2P and Smad4 expression. Loss of Smad signaling was not associated with any particular histological subtype, histological or nuclear grade, estrogen- or progesterone receptor expression, or HER2/neu expression. Loss of Smad4 was inversely correlated with the presence of axillary lymph node metastases. Most importantly, among patients with stage II breast cancer, lack of Smad2P expression in the tumor was strongly associated with shorter overall survival. Finally, analysis of a small cohort of hereditary breast cancers failed to reveal any association between BRCA1 or BRCA2 genotype and alterations in Smad signaling.
Insights
Transforming growth factor-beta (TGF-β) signaling disruptions are linked to breast cancer. In vivo studies show Smad signaling loss in tumors correlates with poorer survival, particularly in stage II breast cancer patients.
Area of Science:
- Oncology
- Molecular Biology
- Cell Signaling
Background:
- Transforming growth factor-beta (TGF-β) signaling is implicated in human breast cancer development and progression.
- Previous research relied heavily on in vitro cell lines and mouse models, leaving in vivo mechanisms in human breast cancer largely unknown.
- Understanding TGF-β pathway disruptions in human breast tumors is crucial for identifying novel therapeutic targets.
Purpose of the Study:
- To investigate the expression and activation patterns of Smad proteins, key postreceptor components of the TGF-β pathway, in human breast carcinoma specimens.
- To compare these in vivo findings with those observed in human breast cancer cell lines.
- To correlate Smad signaling status with clinical parameters and patient outcomes.
Main Methods:
- Analysis of Smad2, Smad2 phosphorylation (Smad2P), and Smad4 expression in human breast cancer cell lines.
- Assessment of TGF-β-induced growth arrest and Smad2 phosphorylation in vitro.
- Evaluation of Smad2, Smad2P, and Smad4 expression in 456 human breast carcinoma tissue microarrays.
- Correlation of Smad signaling status with histological features, receptor expression, lymph node metastasis, and patient survival.
Main Results:
- Breast cancer cell lines showed variable Smad signaling, with some lacking TGF-β receptor or Smad4 expression.
- The majority of primary breast tumors (92%) expressed Smad2, Smad2P, and Smad4, indicating intact signaling.
- Loss of Smad2P (6.6%) or Smad4 (2%) was observed in a subset of tumors.
- Loss of Smad4 inversely correlated with lymph node metastasis.
- Lack of Smad2P expression was significantly associated with shorter overall survival in stage II breast cancer patients.
- No association was found between Smad signaling alterations and BRCA1/2 genotype in hereditary breast cancers.
Conclusions:
- In vivo Smad signaling phenotypes in human breast tumors largely mirror those of cell lines.
- Loss of Smad2P expression is a significant prognostic marker for reduced survival in stage II breast cancer.
- Disruptions in TGF-β/Smad signaling may play a role in breast cancer progression and metastasis.