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TRAF-4 expression in epithelial progenitor cells. Analysis in normal adult, fetal, and tumor tissues
M Krajewska1, S Krajewski, J M Zapata
1Burnham Institute, La Jolla, CA 92037, USA.
Abstract:
TRAF-4 was discovered because of its expression in breast cancers and is a member of the tumor necrosis factor (TNF) receptor-associated factor (TRAF) family of putative signal-transducing proteins. In vitro binding assays demonstrated that TRAF-4 interacts with the cytosolic domain of the lymphotoxin-beta receptor (LT beta R) and weakly with the p75 nerve growth factor receptor (NGFR) but not with TNFR1, TNFR2, Fas, or CD40. Immunofluorescence analysis of TRAF-4 in transfected cells demonstrated localization to cytosol but not nucleus. Immunohistochemical assays of normal human adult tissues revealed prominent cytosolic immunostaining in thymic epithelial cells and lymph node dendritic cells but not in lymphocytes or thymocytes, paralleling the reported patterns of LT beta R expression. The basal cell layer of most epithelia in the body was very strongly TRAF-4 immunopositive, including epidermis, nasopharynx, respiratory tract, salivary gland, and esophagus. Similar findings were obtained in 12- to 18-week human fetal tissue, indicating a highly restricted pattern of expression even during development in the mammary gland, epithelial cells of the terminal ducts were strongly TRAF-4 immunopositive whereas myoepithelial cells and most of the mammary epithelial cells lining the extralobular ducts were TRAF-4 immunonegative. Of 84 primary breast cancers evaluated, only 7 expressed TRAF-4. Ductal carcinoma in situ (DCIS) lesions were uniformly TRAF-4 immunonegative (n = 21). In the prostate, the basal cells were strongly immunostained for TRAF-4, whereas the secretory epithelial cells were TRAF-4 negative. Basal cells in prostate hypertrophy (n = 6) and prostatic intraepithelial neoplasia (PIN; n = 6) were strongly TRAF-4 positive, but none of the 32 primary and 16 metastatic prostate cancer specimens examined contained TRAF-4-positive malignant cells. Although also expressed in some types of mesenchymal cells, these findings suggest that TRAF-4 is a marker of normal epithelial stem cells, the expression of which often ceases on differentiation and malignant transformation.
Insights
Tumor necrosis factor receptor-associated factor 4 (TRAF-4) is expressed in normal epithelial stem cells but not typically in differentiated or malignant cells. Its expression is restricted in various tissues, suggesting a role in maintaining epithelial stem cell populations.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- Tumor necrosis factor receptor-associated factor 4 (TRAF-4) is a protein involved in signal transduction.
- TRAF-4 was initially identified due to its expression in breast cancers.
- TRAF-4 belongs to the TNF receptor-associated factor family.
Purpose of the Study:
- To investigate the expression pattern and cellular localization of TRAF-4 in normal human tissues and cancers.
- To determine if TRAF-4 can serve as a marker for normal epithelial stem cells or cancer.
Main Methods:
- In vitro binding assays to assess TRAF-4 interactions with known receptors.
- Immunofluorescence and immunohistochemical assays to determine TRAF-4 localization and expression in various human tissues (adult, fetal, cancerous, and pre-cancerous).
- Evaluation of TRAF-4 expression in primary breast cancers, DCIS, prostate cancer, prostate hypertrophy, and PIN.
Main Results:
- TRAF-4 interacts with the lymphotoxin-beta receptor (LT beta R) and weakly with NGFR, but not TNFR1, TNFR2, Fas, or CD40.
- TRAF-4 is localized to the cytosol, not the nucleus.
- TRAF-4 shows prominent expression in the basal cells of most epithelia (epidermis, respiratory tract, salivary gland, esophagus, prostate) and thymic epithelial cells/lymph node dendritic cells, indicating restricted expression in normal tissues.
- TRAF-4 expression was found in epithelial cells of mammary terminal ducts during fetal development.
- TRAF-4 was largely absent in primary breast cancers (7/84) and uniformly negative in DCIS (21/21).
- Prostate basal cells were TRAF-4 positive, but malignant prostate cancer cells (primary and metastatic) were TRAF-4 negative.
Conclusions:
- TRAF-4 expression is characteristic of normal epithelial stem cells.
- TRAF-4 expression often diminishes upon differentiation and malignant transformation.
- TRAF-4 may serve as a valuable marker for identifying normal epithelial stem cells and distinguishing them from malignant cells in breast and prostate tissues.