Isolation and characterization of an embryonal carcinoma cell line lacking SSEA-1 antigen

Stage-specific embryonic antigen 1 (SSEA-1) is a glycoconjugate that is expressed on embryonal carcinoma cells but not on their differentiated derivatives. To determine if SSEA-1 is required for the expression of the EC cell phenotype, a variant cell line lacking this antigen was isolated by exposing mutagenized OTF9-63 (an F9 subclone) cells to anti-SSEA-1 antiserum plus complement. Indirect cytotoxicity tests demonstrated that the variant cell line exhibits at least a 500-fold reduction in SSEA-1 expression. Somatic cell hybrids constructed between variant and wild-type cells expressed SSEA-1, suggesting that the lack of SSEA-1 expression in the mutant is probably due to loss, rather than masking, of the antigenic site. The variant cell line was tumorigenic in syngeneic mice, forming teratocarcinomas composed exclusively of embryonal carcinoma cells. Monolayer cultures of the variant cell line formed parietal endodermal (laminin-positive) cells following exposure to retinoic acid whereas aggregates grown in suspension culture formed visceral endoderm. Also, like their parental cells, the variant cells sorted out to form simple embryoid bodies when mixed in suspension with parietal-like endodermal cells. Thus, the expression of a number of aspects of the embryonal carcinoma phenotype is not dependent on the presence of SSEA-1.