Dissociation Between Release and Gene Expression of Gonadotropin α-Subunit in Gonadotropin-Releasing Hormone-Stimulated αT3-1 Cell Line

The aT3-l cell line which was derived by targeted tumorigenesis in transgenic mice [Windle et al. (1990) Mol. Endocrinol. 4, 597-603] possesses high-affinity binding sites for GnRH analogs coupled to enhanced phosphoinositideturnover and phospholipase D activity. Incubation of aT3-1 cells with [D-Trp⁶]-GnRH analog (GnRH-A) resulted in a rapid increase in gonadotropin a-subunit mRNA levels which was detected already at 30 min of incubation (0.1 nM GnRH-A, 3-fold, p 0.01). The effect diminished with time to reach basal levels at about 12 h of incubation, with a secondary rise in a mRNA levels between 12 and 24 h of incubation. Addition of the protein kinase C activator 12-O-tetradecanoylphorbol 13-acetate (TPA, 100 ng/mL) or the Ca²⁺ ionophore ionomycin (1 MM) to aT3-l cells also resulted in a rapid increase in subunit mRNA levels. Surprisingly, GnRH-induced a-subunit release was detected only after a lag of 4 h of incubation. Thus, dissociation between exocytosis and gene expression can be demonstrated in GnRH-stimulated aT3-l cell line.