Mechanism of induction of prolactin synthesis in GH cells

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Abstract
Prolactin-specific RNA (RNAPRL) in total nuclear RNA and in cytoplasmic poly(A)+RNA isolated from GH (rat pituitary tumor) cells was selectively hybridized to immobilized cloned complementary [c]DNAPRL. Agarose gel electrophoresis of the nuclear RNAPRL sequences eluted from the nitrocellulose filters revealed several RNA species of .apprx. 25-30, 18-19 and 12-13 S. Only the 12-13 S RNA species could be detected in the cytoplasmic poly(A)+RNA fraction. Comparative analysis of total nuclear RNA of control and TRH-treated cells by the reverse Southern blot technique demonstrated increased levels of all the nuclear RNAPRL species in hormone-treated cells. Nuclear and cytoplasmic RNAPRL sequences in control and treated cells were quantitated by molecular hybridization to cloned cDNAPRL. The 2- to 3-fold stimulation of PRL production by TRH-treated GH4C1 cells could be correlated to the corresponding increase of nuclear RNAPRL sequences. The hybrid strain, which produces 1/5th the amount of PRL that the parent GH4C1 does, had 1/5th the amount of nuclear RNAPRL sequences. TRH affected neither prolactin production nor nuclear RNAPRL level in 928-9b cells. RNAPRL sequences could not be detected either in nuclei or in cytoplasm of prolactin nonproducing F1BGH12C1 cells. Prolactin production could be induced and RNAPRL sequences could be detected in the total nuclear RNA and in cytoplasmic poly(A)+RNA fraction after treatment of this GH cell substrain with 5-bromodeoxyuridine. Differential basal prolactin production and its modulation by TRH and by 5-bromodeoxyuridine can be correlated to the altered levels of nuclear RNAPRL sequences in the 3 GH cell strains.