Prolactin Signaling through the Short Form of Its Receptor Represses Forkhead Transcription Factor FOXO3 and Its Target Gene Galt Causing a Severe Ovarian Defect

Abstract

Prolactin (PRL) is a hormone with over 300 biological activities. Although the signaling pathway downstream of the long form of its receptor (RL) has been well characterized, little is known about PRL actions upon activation of the short form (RS). Here, we show that mice expressing only RS exhibit an ovarian phenotype of accelerated follicular recruitment followed by massive follicular death leading to premature ovarian failure. Consequently, RS-expressing ovaries of young adults are depleted of functional follicles and formed mostly by interstitium. We also show that activation of RS represses the expression of the transcription factor Forkhead box O3 (FOXO3) and that of the enzyme galactose-1-phosphate uridyltransferase (Galt), two proteins known to be essential for normal follicular development. Our finding that FOXO3 regulates the expression of Galt and enhances its transcriptional activity indicates that it is the repression of FOXO3 by PRL acting through RS that prevents Galt expression in the ovary and causes follicular death. Coexpression of RL with RS prevents PRL inhibition of Galt, and the ovarian defect is no longer seen in RS transgenic mice that coexpress RL, suggesting that RL prevents RS-induced ovarian impairment. In summary, we show that PRL signals through RS and causes, in the absence of RL, a severe ovarian pathology by repressing the expression of FOXO3 and that of its target gene Galt. We also provide evidence of a link between the premature ovarian failure seen in mice expressing RS and in mice with FOXO3 gene deletion as well as in human with Galt mutation.

Subfertility and growth restriction in a new galactose-1 phosphate uridylyltransferase (GALT) - deficient mouse model

“…Our mouse model thus confirms the importance of GALT activity in ovarian function, independently from other genes or exogenous factors that confounded the previous experimental approaches of experimental hypergalactosemia 39,40 and artificial activation of the prolactin short form receptor in the ovary. 41 As for the absence of sepsis and bleeding disorder in the intoxicated newborn pups, there is serotype specificity of the Escherichia coli involved in human sepsis 42,43 and this specific bacterial species may be absent in the normal flora of the murine species. The lack of bleeding disorder, which was previously thought to be predominantly due to liver failure, may also be explained by inter-species differences in glycosylation between humans and mice.…”

Cloning and expression of a unique short form of the porcine prolactin receptor

“…Gibori et al have specifically studied the mPRLR-PR1 by generating mice that are transgenic for this isoform in a PRLRKO background. The resultant phenotype of these mice is striking in that they undergo accelerated follicular recruitment followed by massive follicular death that leads to premature ovarian failure (Halperin et al 2008). Using this model, Halperin et al (2008) identified that Foxo3 and Galt are two downstream targets of the mPRLR-PR1, where both of these are implicated during clinical ovarian failure in humans.…”

“…The resultant phenotype of these mice is striking in that they undergo accelerated follicular recruitment followed by massive follicular death that leads to premature ovarian failure (Halperin et al 2008). Using this model, Halperin et al (2008) identified that Foxo3 and Galt are two downstream targets of the mPRLR-PR1, where both of these are implicated during clinical ovarian failure in humans. This group also established that the mPRLR-PR1 mediates specific signaling pathways including downregulation of Sp1 target genes (Devi et al 2009).…”

“…The efficacy of hPRLRSF1b as a dominant negative may lie in its ability to accelerate hPRLR-LF mRNA degradation (Tan & Walker 2010) as well as its ability to heterodimerize with hPRLR-LF to block signaling (Tan et al 2005). In contrast, there is little data on the dominant-negative effectiveness of mPRLR-PR1 (Halperin et al 2008) and no data exist for mPRLR-PR2, mPRLR-PR3, or the ovine, bovine, caprine, or carp short PRLR isoforms, although it has been suggested that the ovine PRLR-SF may act as a dominant negative (Cassy et al 1998).…”

“…Second, when 3T3 fibroblasts were transfected with one short form of the mouse Prlr (mPrlr-PR1) they proliferated in response to PRL, suggesting that this mPRLR-SF isoform transduced a mitogenic signal in the absence of the mPRLR-LF (Das & Vonderhaar 1995). The mPRLR-PR1 also represses Forkhead box O3 (Foxo3) and galactose-1-phosphate uridyltransferase (Galt) expression in the mouse ovary, leading to premature follicular death (Halperin et al 2008). Finally, failure of heterozygous Prlr knockout (PRLRKO) mice to lactate after their first pregnancy can be rescued by overexpression of mPRLR-PR1 in the mammary gland (Binart et al 2003).…”