Counter-selection for over-expressed human CD44s in primary tumors versus lung metastases in a mouse fibrosarcoma
1Department of Molecular Biology, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106, USA.
Abstract:
Human CD44 standard isoform cDNA (hCD44s) was transfected into sis-transformed Balb/c 3T3 cells and into ras-revertant IIIA4 cells (both tumorigenic but nonmetastatic). Transfectants were injected subcutaneously into athymic nude mice to elucidate the functional role of hCD44s over-expression in progression and metastasis. The transfectants (but not parental cells) were capable of lung micrometastasis and of binding exogenously-added hyaluronan. hCD44s protein expression was conserved in lung micrometastases suggesting that it may have been necessary for their formation. In contrast, no hCD44s protein was detected in large subcutaneous (s.c.) tumors but normal levels of murine CD44 were detected. A second round of tumor development, using these two tumor cell classes, demonstrated that hCD44s-nonexpressing s.c. tumor cells re-expressed it in lung micrometastases. Conversely, hCD44s-expressing lung micrometastatic cells, when injected into a second group of mice, downregulated hCD44s expression in order to grow sizable s.c. tumors. S.c. tumor cells still contained the hCD44s gene but its expression was inhibited by epigenetic mechanisms, one of which was shown to be methylation of the hCD44s gene. These studies demonstrate (a) opposing selective pressures on CD44s over-expression for s.c. tumor growth and for metastatic spread to the lung and (b) further credence for the significance of CD44 for metastatic spread of fibrosarcomas. Therefore, CD44s may be a critical component of the metastatic phenotype induced by specific oncogenes.
Insights
Over-expression of human CD44 standard isoform (hCD44s) promotes lung metastasis but hinders subcutaneous tumor growth in fibrosarcomas. Epigenetic mechanisms, like gene methylation, regulate hCD44s expression, highlighting its critical role in the metastatic phenotype.
Area of Science:
- Oncology
- Molecular Biology
- Cancer Metastasis
Background:
- CD44 is a cell surface glycoprotein involved in cell-cell and cell-matrix adhesion.
- The standard isoform of human CD44 (hCD44s) plays a role in cancer progression and metastasis.
- Understanding the regulation of hCD44s expression is crucial for developing targeted cancer therapies.
Purpose of the Study:
- To investigate the functional role of hCD44s over-expression in tumor progression and metastasis.
- To elucidate the selective pressures influencing hCD44s expression during different stages of cancer spread.
- To identify the regulatory mechanisms controlling hCD44s expression in fibrosarcomas.
Main Methods:
- Transfection of hCD44s cDNA into tumorigenic, nonmetastatic Balb/c 3T3 and IIIA4 cells.
- Subcutaneous injection of transfectant cells into athymic nude mice.
- Analysis of hCD44s protein expression in primary tumors and lung micrometastases.
- Investigation of epigenetic regulation, including gene methylation, of hCD44s expression.
Main Results:
- hCD44s over-expressing cells formed lung micrometastases and bound hyaluronan.
- hCD44s protein was essential for lung micrometastasis formation but downregulated in large subcutaneous tumors.
- Subcutaneous tumor cells re-expressed hCD44s in lung micrometastases, while metastatic cells downregulated it for subcutaneous growth.
- Epigenetic mechanisms, including methylation, inhibited hCD44s gene expression in subcutaneous tumors.
Conclusions:
- Opposing selective pressures exist for hCD44s over-expression in subcutaneous tumor growth versus metastatic spread.
- hCD44s is a significant factor in the metastatic spread of fibrosarcomas.
- hCD44s may be a critical component of the metastatic phenotype induced by specific oncogenes.
