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A metastatic tumor cell line has greatly reduced levels of a specific homotypic cell adhesion molecule activity
1Department of Chemistry and Biochemistry, University of California, Los Angeles 90024-1569.
Abstract:
The first step in tumor metastasis is the detachment of cells from the primary tumor. If metastatic tumor cells have decreased levels of active homotypic cell adhesion molecules (CAMs), this might aid their escape from the primary tumor. In order to determine whether homotypic CAM activity might be reduced in metastatic cells, a new direct CAM assay was developed. The assay gave a linear response with respect to the concentration of a CAM fragment preparation from Balb/3T3 cells and was able to follow partial purifications of the CAM activity. The yield of homotypic CAM activity was measured from metastatic cells, related tumorigenic but nonmetastatic cells, and parental cells. The parental Balb/3T3 and nonmetastatic Balb/3T3 MSV85 cells yielded 22.5 +/- 1.1 (SD) and 24.8 +/- 3.5 units of CAM activity per mg of protein, whereas the metastatic Balb/3T3 K234 cells yielded only 4.6 +/- 0.8 units/mg. The homotypic adhesiveness of each of the cell lines was closely correlated with the level of CAM activity. When the CAM activity from each of the three cell lines was serially fractionated with the same column, the parental Balb/3T3 and nonmetastatic Balb/3T3 MSV85 cells each had one major peak of CAM activity that eluted in the same place. However, the metastatic Balb/3T3 K234 cells were missing this peak of CAM activity. These results suggest that levels of homotypic CAM activity are greatly reduced in a metastatic cell line because the cells are missing a specific CAM activity. This would presumably allow the metastatic cells to escape more easily from the primary tumor and provide a molecular explanation for how they can complete the first step in metastasis.
Insights
Metastatic tumor cells exhibit significantly reduced levels of active homotypic cell adhesion molecules (CAMs), a key factor enabling their detachment and escape from primary tumors. This study developed a new assay to quantify CAM activity, revealing a specific CAM deficiency in metastatic cells.
Area of Science:
- Cell Biology
- Cancer Research
- Molecular Biology
Background:
- Tumor metastasis initiation involves cell detachment from the primary tumor.
- Reduced homotypic cell adhesion molecule (CAM) activity in metastatic cells may facilitate their escape.
- Understanding CAMs is crucial for explaining the initial steps of metastasis.
Purpose of the Study:
- To determine if metastatic cells have reduced homotypic CAM activity.
- To develop and validate a direct assay for measuring CAM activity.
- To investigate the correlation between CAM activity and cell adhesiveness in metastatic and non-metastatic cells.
Main Methods:
- Development of a novel direct assay for homotypic cell adhesion molecule (CAM) activity.
- Quantification of CAM activity in parental, non-metastatic, and metastatic cell lines (Balb/3T3, Balb/3T3 MSV85, and Balb/3T3 K234).
- Serial fractionation of CAM activity using column chromatography to identify specific CAM peaks.
Main Results:
- Metastatic Balb/3T3 K234 cells showed significantly lower homotypic CAM activity (4.6 units/mg) compared to parental (22.5 units/mg) and non-metastatic cells (24.8 units/mg).
- Homotypic cell adhesiveness strongly correlated with measured CAM activity levels across all cell lines.
- Metastatic cells lacked a specific peak of CAM activity found in parental and non-metastatic cells, indicating a deficiency in a particular CAM.
Conclusions:
- Greatly reduced homotypic CAM activity in metastatic cells is linked to the absence of a specific CAM.
- This deficiency in CAM activity provides a molecular mechanism for enhanced cell detachment, facilitating the first step of tumor metastasis.
- The findings offer a molecular explanation for how metastatic cells escape the primary tumor.