THE SMALL-CELL LUNG-CANCER ANTIGEN CLUSTER-4 AND THE LEUKOCYTE ANTIGEN CD24 ARE ALLELIC ISOFORMS OF THE SAME GENE (CD24) ON CHROMOSOME BAND6Q21

Cluster-4 and CD24 cDNA's have recently been cloned from the small cel l lung carcinoma (SCLC) cell line SW2 and from the erythroleukemia cel l line K562, respectively. The only difference in the coding sequence, between cluster-4 and CD24 antigens is the substitution of a single b ase pair leading to a substitution of Val by Ala near the putative gly cosylphosphatidylinositol (GPI) anchorage sites of the mature protein. Here we demonstrate that the nucleotide substitution which distinguis hes the cluster-4 and CD24 antigen genes is due to an allelic polymorp hism on chromosome band 6q21. In addition, we identified by Southern b lotting and PCR of DNA from somatic human x hamster hybrid cell lines homologues of cluster-4/CD24 on the Y chromosome and chromosome 15. We suggest, however, that the gene on 6q21 is the active locus since the mRNA of cell lines always represents the allelic variants found on ch romosome 6. The distribution pattern of this allelic polymorphism in S CLC cell lines and leukocytes of healthy donors did not reveal any obv ious relationship with disease. However, it is noteworthy that homozyg osity for cluster-4 was found in only one case whereas heterozygosity and homozygosity for CD24 both contribute up to 50% of the samples exa mined.