Different Biological Effects of Unmodified Prolactin and a Molecular Mimic of Phosphorylated Prolactin Involve Different Signaling Pathways
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- 作者：Wei Wu ; Djurdjica Coss ; Mary Y. Lorenson ; C. Benson Kuo ; Xiaolei Xu ; and Ameae M. Walker
- 刊名：Biochemistry
- 出版年：2003
- 出版时间：June 24, 2003
- 年：2003
- 卷：42
- 期：24
- 页码：7561 - 7570
- 全文大小：134K
- 年卷期：v.42,no.24(June 24, 2003)
- ISSN：1520-4995
文摘
Previous work has shown that naturally phosphorylated prolactin antagonizes the growth-promoting activities of unmodified prolactin (U-PRL) and that this effect is duplicated by a molecularmimic, S179D PRL. At the same time, the S179D PRL is a superagonist with regard to expression ofsome PRL-regulated genes. We have asked whether the different activities of U-PRL and S179D PRLare the result of differential signaling. HC11 cells (a normal mouse mammary cell line) were grown toconfluence, primed with hydrocortisone, and then exposed to the PRLs. A 15 min incubation of PRL-naive cells led to substantial tyrosine phosphorylation of Jak 2 and Stat 5a by U-PRL and an essentiallyequivalent Jak 2 activation by S179D PRL. The latter, however, was accompanied by reduced tyrosinephosphorylation of Stat 5a. EMSA analysis using a Stat 5 binding site showed both PRLs to cause equivalentbinding of nuclear proteins and that most of what bound was complexed through Stat 5a. Phosphoaminoacid analysis of Stat 5 showed S179D PRL to double the amount of serine phosphorylation versus thatseen with U-PRL. Analysis of the MAP kinase pathway showed U-PRL capable of activation of ERKs1 and 2 but that signaling via ERKs 1 and 2 was greater with S179D PRL. A 7-day incubation in eitherPRL increased 
-casein mRNA levels, but S179D PRL caused a 2-fold increase over that seen withU-PRL. The increase, over that seen with U-PRL, was blocked by the MAP kinase inhibitor, PD98059.After 7 days of treatment with S179D PRL, expression of the short PRL receptor was doubled, and signalingshowed a greater dependence on the MAP kinase pathway (2.9-fold increase in ERK 1 and 2 activation).We conclude that although both PRLs use both pathways to some extent, U-PRL signals primarily throughJak 2-Stat 5 whereas S179D PRL signals primarily through the MAP kinase pathway especially afterprolonged exposure. This is the first demonstration of differential involvement of signaling pathways bydifferent forms of PRL.
-casein mRNA levels, but S179D PRL caused a 2-fold increase over that seen withU-PRL. The increase, over that seen with U-PRL, was blocked by the MAP kinase inhibitor, PD98059.After 7 days of treatment with S179D PRL, expression of the short PRL receptor was doubled, and signalingshowed a greater dependence on the MAP kinase pathway (2.9-fold increase in ERK 1 and 2 activation).We conclude that although both PRLs use both pathways to some extent, U-PRL signals primarily throughJak 2-Stat 5 whereas S179D PRL signals primarily through the MAP kinase pathway especially afterprolonged exposure. This is the first demonstration of differential involvement of signaling pathways bydifferent forms of PRL.