GONADAL TUMORIGENESIS IN TRANSGENIC MICE BEARING THE MOUSE INHIBIN ALPHA-SUBUNIT PROMOTER SIMIAN-VIRUS T-ANTIGEN FUSION GENE - CHARACTERIZATION OF OVARIAN-TUMORS AND ESTABLISHMENT OF GONADOTROPIN-RESPONSIVE GRANULOSA-CELL LINES

To establish in vivo gonadal tumor models and permanent lines of gonad al somatic cells we produced transgenic (TG) mice expressing the Simia n virus (SV) 40 T-antigens (T-ag), driven by 6 or 2.1 kilobase fragmen ts of the mouse inhibin alpha-subunit promoter. Hitherto, altogether 4 4 TG mice, one of which carried the shorter transgene, have produced g onadal tumors. Two founder females expressing the longer transgene, KK 1 and KK3, and three established TG mouse lines were studied in detail . Penetrance of the phenotype in IT6-M and IT6-F mouse lines was 100% (tumors/TG: IT6-M 22/22, IT6-F 14/14). The T-ag mRNA was strongly expr essed in the gonads, adrenal glands, pituitary, and brain. The KK-1 an d KK-3 ovarian tumor cells immunostained with anti-SV40 large-T antibo dy. The KK-1 cells possessed high-affinity LH receptors [equilibrium a ssociation constant (K-a = 7.8 x 10(10) liters/mol] and responded to h uman CG by elevated cAMP and progesterone production. Also FSH slightl y stimulated their cAMP and estradiol production (P < 0.01). These cel ls expressed cytochrome P450(arom) and inhibin a mRNA, but not cytochr ome P450(c17 alpha). In conclusion, the KK-1 cells are immortalized lu teinizing granulosa cells expressing endogenous gonadotropin receptors , steroidogenic enzymes, and inhibin alpha. These cells will be useful in studies on the molecular aspects of granulosa cell function. The p resent study indicates that the 6-kilobase fragment of the inhibin a p romoter described in this article contains the elements directing tiss ue-specific expression in vivo and is useful for targeted expression o f other genes in the gonads.