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Identification and purification of 115- and 125-kilodalton cell surface human melanoma-associated antigens
Abstract:
Surface macromolecules shed into culture medium by radioiodinated human melanoma cells were fractionated on Sepharose 6B and by sequential lectin-affinity chromatography. Radioactivity associated with melanoma-associated antigens (MAAs) was assayed by indirect immunoprecipitation with anti-melanoma serum. Two MAAs were separated and highly purified. Both antigens were single-chain glycoproteins expressed on many, but not all, melanoma cells but undetectable on normal melanocytes and a variety of unrelated normal, fetal, and malignant cells. One MAA, with a molecular mass of approximately 115 kd, eluted on Sepharose 6B in a lower molecular mass peak and had a high affinity for ricin lectin. The carbohydrate side chain of this antigen contained D-galactose. The other MAA, with a molecular mass of approximately 125 kd, eluted on Sepharose 6B in a peak of higher molecular mass and had a high affinity for wheat germ lectin. The carbohydrate side chain of this antigen contained sialic acid. Both antigens were highly purified. By sodium dodecyl sulfate-poly-acrylamide gel electrophoresis analysis, no contaminating proteins were present in the purified 115-kd MAA fraction, and only a single minor contaminant was present in the fraction containing the purified 125-kd MAA. These two antigens differed in their biochemical or immunological properties from other MAAs of similar size that have been previously described.
Insights
Researchers purified two novel melanoma-associated antigens (MAAs) shed by melanoma cells. These glycoproteins, with distinct carbohydrate side chains, show promise as specific cancer biomarkers.
Area of Science:
- Biochemistry
- Immunology
- Oncology
Background:
- Melanoma cells shed surface macromolecules into the culture medium.
- Melanoma-associated antigens (MAAs) are potential targets for cancer diagnosis and therapy.
Purpose of the Study:
- To isolate and characterize novel MAAs from human melanoma cells.
- To determine the biochemical properties and cell expression patterns of these MAAs.
Main Methods:
- Radioiodination of human melanoma cells followed by collection of shed macromolecules.
- Fractionation using Sepharose 6B chromatography and sequential lectin-affinity chromatography.
- Assay of MAA-associated radioactivity via indirect immunoprecipitation with anti-melanoma serum.
- Analysis of purified antigens using SDS-PAGE.
Main Results:
- Two distinct MAAs were successfully separated and highly purified.
- One MAA (115 kd) contained D-galactose and bound to ricin lectin; the other (125 kd) contained sialic acid and bound to wheat germ lectin.
- Both MAAs were expressed on many melanoma cells but not on normal melanocytes or other tested cell types.
- Purified antigens showed minimal protein contamination, with the 115-kd MAA being exceptionally pure.
Conclusions:
- Two novel melanoma-associated antigens with unique biochemical properties were identified.
- These MAAs represent potential specific biomarkers for human melanoma.
- The findings differentiate these MAAs from previously described antigens of similar molecular weight.