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  • Title: Characteristics of the prolactin stimulation of c-fos mRNA levels in mouse mammary gland explants.
    Author: Rillema JA, Rowady DL.
    Journal: Proc Soc Exp Biol Med; 1996 Jun; 212(2):142-6. PubMed ID: 8650251.
    Abstract:
    The signal transduction pathway(s) for the prolactin (PRL) regulation of lactogenic processes in the mammary are not fully known. Recent studies indicate that the PRL occupancy of its receptor activates a tyrosine kinase (JAK-2), which is constitutively associated with the receptor. In the present studies, we have characterized the PRL stimulation of c-fos mRNA accumulation in mouse mammary gland explants that were precultured with insulin and cortisol for 36 hr. In time course studies, an initial effect (2-fold increase) of PRL was apparent after 15 min, a 4-fold increase occurred after 60 min, and a 2-fold increase was apparent after 2 hr. Dose-response experiments indicated an initial effect with 5 ng/ml PRL and a maximum effect with 500 ng/ml PRL. The accumulation of c-fos; mRNA in the cultured mammary tissues was also increased by human GH, recombinant bovine PRL, cycloheximide, and phorbol 12-myristate 13-acetate (TPA). The cycloheximide and PRL responses were additive, thus indicating that cycloheximide did not "superinduce" the PRL stimulation of c-fos mRNA accumulation. Downregulation of protein kinase C (PKC) by pretreating mammary tissues for 1 day with TPA did not affect the magnitude of the PRL stimulation of c-fos mRNA accumulation. The findings from these studies are consistent with c-fos playing a role in the PRL stimulation of lactogenic processes in the mammary gland. PRL had no effect on c-jun mRNA accumulation under any of the experimental conditions employed in the c-fos studies.
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