Mechanism of induction of prolacti (thyroliberin/nuclear precursor/cytoplasmic mRNA/selection hybridi

Prolactin-specific RNA (RNApRL) in total nuclear RNA and in cytoplasmic poly(A)+RNA isolated from GH (rat pi- tuitary) cells was selectively hybridized to immobilized cloned cDNApRL. Agarose gel electrophoresis of the nuclear RNApRL se- quences eluted from the nitrocellulose filters revealed several RNA species of approximately 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 thyrotropin-releasing hormone (thyroliberin)-treated cells by the reverse Southern blot technique demonstrated in- creased levels of all the nuclear RNApRL species in hormone- treated cells. Nuclear and cytoplasmic RNApRL sequences in con- trol and treated cells were quantitated by molecular hybridization to cloned cDNApRL. The 2-to 3-fold stimulation of PRL production by thyrotropin-releasing hormone-treated GH4C1 cells could be correlated to the corresponding increase of nuclear RNApRL se- quences. The hybrid strain, which produces 1/5th the amount of PRL that the parent GH4Cl does, had 1/5th the amounts of nu- clear RNApRL sequences. Thyrotropin-releasing hormone af- fected 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 FiBGH12C1 cells. However, 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. These results demon- strate that differential basal prolactin production and its modu- lation by thyrotropin-releasing hormone and by 5-bromodeoxy- uridine can be correlated to the altered levels of nuclear RNApRL sequences in the three GH tell strains.