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CD24, a signal-transducing molecule expressed on human B cells, is a major surface antigen on small cell lung
Abstract:
Cell lines derived from human small cell carcinoma of the lung express high levels of a surface polypeptide termed the cluster-w4 antigen, which was previously identified as a potential target for toxin-based immunotherapy of lung cancer. We have cloned a complementary DNA encoding the cluster-w4 antigen from COS-1 fibroblasts transfected with a SW2 small cell carcinoma library, by panning with a mixture of the cluster-w4-specific monoclonal antibodies SWA11, SWA21, and SWA22. The sequence of the cluster-w4 complementary DNA encodes an unusually short (80-amino acid) protein identical to that recently reported for the leukocyte activation molecule CD24 except for a single valine-alanine substitution due to a single-base polymorphism within the region of the gene coding for the extracellular domain. Biochemical analyses of the cloned cluster-w4 antigen confirmed both the presence of the phosphatidylinositol tail and the extensive glycosylation reported for the CD24 molecule. Furthermore, the cloned cluster-w4 antigen expressed on COS cells was shown to react with a comprehensive panel of CD24-specific monoclonal antibodies, as assessed by indirect immunofluorescence staining. Northern blot hybridization indicated the presence of several transcript sizes for the cluster-w4 antigen that were greatly overexpressed in small cell carcinoma cell lines, compared with normal hemopoietic cells and CD24-positive cell lines. Southern blot hybridization of restriction digests of genomic DNA identified a complex pattern of bands consistent with either a complex gene structure containing many exons or the presence of a family of closely related genes.
Insights
Researchers identified the cluster-4 antigen, a potential immunotherapy target for lung cancer, as the leukocyte activation molecule CD24. This finding advances understanding of small cell lung cancer cell surface markers.
Area of Science:
- Oncology
- Immunology
- Molecular Biology
Background:
- Small cell lung carcinoma (SCLC) cell lines overexpress the cluster-4 antigen.
- The cluster-4 antigen is a potential target for toxin-based immunotherapy in lung cancer.
- Previous identification of cluster-4 as a surface polypeptide.
Purpose of the Study:
- To clone the complementary DNA (cDNA) encoding the cluster-4 antigen.
- To characterize the cluster-4 antigen and its relationship to known molecules.
- To investigate the expression patterns of the cluster-4 antigen in cancer versus normal cells.
Main Methods:
- cDNA cloning using COS-1 fibroblasts and monoclonal antibody panning.
- Sequence analysis of the cloned cDNA.
- Biochemical analyses (phosphatidylinositol tail, glycosylation).
- Immunofluorescence staining with CD24-specific antibodies.
- Northern and Southern blot hybridization for gene expression and structure analysis.
Main Results:
- The cluster-4 antigen cDNA encodes an 80-amino acid protein identical to CD24, with a single amino acid difference.
- Biochemical analysis confirmed a phosphatidylinositol tail and glycosylation, similar to CD24.
- Expressed cluster-4 antigen reacted with CD24-specific monoclonal antibodies.
- Northern blots revealed significant overexpression of multiple cluster-4 transcript sizes in SCLC cell lines compared to normal cells.
- Southern blots suggested a complex gene structure or a gene family for cluster-4.
Conclusions:
- The cluster-4 antigen is the leukocyte activation molecule CD24, sharing structural and biochemical similarities.
- CD24 is significantly overexpressed in small cell lung carcinoma, reinforcing its potential as an immunotherapy target.
- The complex gene structure or family of genes warrants further investigation.