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Characterization of a human cervical carcinoma-associated antigen by lectin binding and immuno-electron microscopy
J J Wang1, S R Roffler, M H Yu
1Department of Biology and Anatomy, National Defense Medical Center, Taipei, Taiwan, Republic of China.
Insights
Monoclonal antibody 1H10 recognizes a chondroitin sulfate glycoprotein or proteoglycan on human cervical tumors. Enzyme digestion and lectin assays revealed the epitope contains N-acetyl-galactosamine residues.
Area of Science:
- Biochemistry
- Immunology
- Oncology
Background:
- Monoclonal antibody (Mab) 1H10 targets an antigen on human cervical tumors.
- Understanding the epitope is crucial for targeted therapies.
Purpose of the Study:
- Characterize the binding specificity and nature of the epitope recognized by Mab 1H10.
- Identify the molecular composition of the tumor-associated antigen.
Main Methods:
- Enzyme digestion (sodium periodate, neuraminidase, hyaluronidase, chondroitinase ABC, trypsin, chymotrypsin) of cell membrane homogenates.
- SDS-PAGE and immunoblotting to analyze antigen recognition.
- In situ electron microscopy to assess Mab 1H10 binding to cells.
- Lectin competition assays using Wheat germ agglutinin (WGA), Ricinus communis agglutinin (RCA), and Concanavalin A.
Main Results:
- Sodium periodate treatment abrogated Mab 1H10 binding.
- Neuraminidase and hyaluronidase partially reduced binding, while chondroitinase ABC eliminated it.
- Trypsin and chymotrypsin reduced antigen molecular weight but not binding intensity.
- WGA and RCA partially blocked Mab 1H10 binding, indicating N-acetyl-galactosamine presence.
- Concanavalin A showed weak binding and did not block Mab 1H10 binding.
Conclusions:
- The tumor-associated antigen recognized by Mab 1H10 is a chondroitin sulfate glycoprotein or proteoglycan.
- The epitope contains N-acetyl-galactosamine residues.
- Mab 1H10 shows specific binding to a defined carbohydrate epitope on cervical tumor cells.
Abstract:
The specific binding and nature of the epitope recognized by monoclonal antibody (Mab) 1H10, which binds an antigen expressed on human cervical tumors, was characterized by enzyme digestion, lectin competition assay and immuno-electron microscopy. Membrane homogenates of CaSki cervical carcinoma cells were digested with various enzymes, then analysed by SDS-PAGE and immunoblotting. Cells grown on coverslips were treated with various enzymes and in situ binding of Mab 1H10 to cells was analysed by electron microscopy. The ability of lectin-conjugates to block Mab 1H10 binding to CaSki cells was also examined. Treatment of samples with sodium periodate abrogated antigen recognition by Mab 1H10. Neuraminidase and hyaluronidase digestion decreased but did not eliminate Mab 1H10 binding to cells in situ. Chondroitinase ABC digestion, in contrast, removed Mab 1H10 binding sites both in vitro and in situ. Trypsin and chymotrypsin digestion of cell membrane homogenates decreased the molecular weight of the Mab 1H10 antigen but did not decrease the binding intensity. Wheat germ agglutinin (WGA) strongly bound to CaSki cells and partially blocked Mab 1H10 binding, indicating that the antigen contains N-acetyl-galactosamine residues at or near the epitope recognized by Mab 1H10. Ricinus communis agglutinin (RCA) exhibited a similar binding pattern to WGA. However, concanavalin A bound only weakly to CaSki cells and was ineffective at blocking Mab 1H10 binding. The tumor-associated antigen recognized by Mab 1H10 is concluded to be a chondroitin sulphate glycoprotein or proteoglycan rather than a mucopolysaccharide or lipoprotein.
