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Decrease in tumor-cell attachment and in a 140-kDa fibronectin receptor correlate with greater expression of multiple
M Rieber1, M A Castillo, M S Rieber
1Centre of Microbiology and Cell Biology, Instituto Venezolano de Investigaciones Científicas, Caracas.
Abstract:
B16 melanoma cells attach to matrix-bound fibronectin but fail to adhere to albumin-coated surfaces supplemented with soluble fibronectin. Attachment to substratum is also decreased in the presence of an adhesion-disrupting antibody, or when cells are seeded on substrates poorly adhesive for these cells, such as collagen gels. We have now investigated some of the more general adhesion-related alterations that occur between flattened and poorly attached cells. Immune blots of octylglucoside extracts with the adhesion-disrupting IgG revealed a 140-kDa component in flattened cells, in contrast to the increased detection of a 54-kDa species in a comparable assay with rounded cells. Surface iodination also showed a decreased external exposure of a 140-kDa fibronectin binding species and an increased labelling in multiple 34-kDa protein species, in cells with decreased attachment to substratum. Analysis of 35S-methionine-labelled cell aggregates cultured on collagen gels also revealed a decrease in the 140-kDa region and a greater labelling of multiple 54-kDa components, compared to the same cells flattened on fibronectin. A change in 54- and 34-kDa species was also seen in matrix-associated components of rounded cells that failed to attach with soluble fibronectin. Since the 34-kDa species increase in poorly adherent cells is mainly detected by iodination, and the 54-kDa species increase in the same cells is partly associated with the corresponding detergent-insoluble matrices, we propose that these 2 novel proteins may relate to cell rounding, through a transmembrane modulation involving both surface membrane and cytoskeletal structures.
Insights
B16 melanoma cells show altered protein expression when attachment fails. Specific 34-kDa and 54-kDa proteins increase in poorly adhering cells, potentially regulating cell shape and adhesion.
Area of Science:
- Cell Biology
- Biochemistry
- Biophysics
Background:
- B16 melanoma cell adhesion is crucial for understanding tumor metastasis.
- Cell attachment is influenced by extracellular matrix proteins like fibronectin and surface properties.
- Previous studies indicate B16 cells exhibit differential adhesion based on substrate and fibronectin availability.
Purpose of the Study:
- To investigate general adhesion-related alterations in flattened versus poorly attached B16 melanoma cells.
- To identify specific protein changes associated with decreased cell substratum attachment.
- To explore the potential role of novel proteins in cell rounding and adhesion modulation.
Main Methods:
- Immune blotting of cell extracts to detect specific protein components.
- Surface iodination to assess external protein exposure.
- Metabolic labeling (35S-methionine) of cell aggregates.
- Analysis of matrix-associated components.
Main Results:
- Flattened cells showed a 140-kDa component, while rounded cells had increased 54-kDa species.
- Poorly adhering cells exhibited decreased external exposure of a 140-kDa fibronectin-binding protein.
- Poorly adhering cells showed increased labeling of multiple 34-kDa proteins via iodination.
- Cell aggregates on collagen gels revealed decreased 140-kDa and increased 54-kDa components compared to cells on fibronectin.
Conclusions:
- Two novel proteins, a 34-kDa species and a 54-kDa species, are identified in poorly adhering B16 melanoma cells.
- The 34-kDa protein increase is primarily detected on the cell surface, while the 54-kDa protein is associated with detergent-insoluble matrices.
- These proteins may play a role in cell rounding through transmembrane modulation involving surface membrane and cytoskeletal structures.