Expression by Transgenesis of a Constitutively Active Mutant Form of the Prolactin Receptor Induces Premature Abnormal Development of the Mouse Mammary Gland and Lactation Failure1

Abstract

Prolactin (PRL) initiates signal transduction by inducing homodimerization of PRL receptor (PRL-R). We have previously developed a mutant form of the PRL-R in which a part of the extracellular domain is deleted. This receptor constitutively activates protein gene transcription. We examined the oligomerization of the mutant PRL-R using two differently epitope-tagged receptors in a coimmunoprecipitation assay. It was shown that mutant receptor dimers were formed in a ligand-independent manner, which may explain the constitutive activity on milk protein gene expression. To study the biological activity of this mutant PRL-R on mammary gland development, we generated two lines of transgenic mice expressing the corresponding cDNA specifically in the mammary epithelial cells. For both transgenic lines, the mammary gland of 8-wk-old virgin mice was overdeveloped with numerous dilated ductal and alveolar structures, whereas only a limited duct network was present in wild-type animals at the same age. During pregnancy, the ducts and alveoli of transgenic mice were more developed than those of control animals. At parturition, the transgenic animals failed to lactate and nourish their offspring, and the involution of the mammary gland was strongly delayed. In conclusion, the expression of a constitutively active PRL-R by transgenesis induces a premature and abnormal mammary development and impairs terminal differentiation and milk production at the end of pregnancy.

Local over-expression of prolactin in differentiating mouse mammary gland induces functional defects and benign lesions, but no carcinoma

“…This phenotype is in good agreement with what was observed in virgin Tg mice expressing PRL or a constitutively active PRLR (Wennbo et al 1997, Gourdou et al 2004. From the first gestational/lactational cycle, which turned on expression of autocrine hPRL, more pronounced morphological abnormalities appeared in young WAP-hPRL animals.…”

“…If one considers the stage of mammary differentiation at which it occurs, however, the occurrence (or not) of adenocarcinoma is probably not so surprising. The Met (Wennbo et al 1997), NRL (Rose-Hellekant et al 2003), and b-lactoglobulin (Gourdou et al 2004) promoters were shown to be constitutively active in these models, therefore, PRLR over-activation involved undifferentiated (virgin) mammary glands. At this stage, cell division appeared to be the major component of the actions induced by PRL excess, and both NRL-PRL and Met-PRL models showed that permanent and long-term (O1 year) Figure 9 hPRL expression in other tissues and non-mammary phenotypes.…”

An obesogenic diet started before puberty leads to abnormal mammary gland development during pregnancy in the rabbit

“…Any modification to this endocrine equilibrium may impact lobulo-alveolar formation during pregnancy and subsequent lactation (Sternlicht et al, 2006). A similar abnormal mammary phenotype had previously been reported in transgenic mice over-expressing a constitutively active prolactin (PRL) receptor (Gourdou et al, 2004), suggesting that the alterations observed in the mammary glands of OD rabbits may be related to a modification of the PRL pathway. However, no differences in the localization of the PRL receptor, or in the phosphorylation of Stat5, were observed between the two groups during preliminary immunolocalization and Western blot experiments (data not shown), but we cannot exclude an alteration to either the expression of the prolactin receptor or its signaling pathway in response to acute PRL stimulation in the OD group (Nevalainen et al, 2002).…”

Identification of a gain-of-function mutation of the prolactin receptor in women with benign breast tumors

“…The cellular effects induced by these artificial variants were very similar to those reported in this study for the natural PrlR I146L mutant. Mammary-specific transgenic mice expressing one of these variants were generated (24). Phenotypes included premature over-development of the gland in virgin and pregnant animals, and, after parturition, impaired terminal differentiation, functional failure, and delayed involution.…”

“…Phenotypes included premature over-development of the gland in virgin and pregnant animals, and, after parturition, impaired terminal differentiation, functional failure, and delayed involution. Unfortunately, this study failed to reveal whether these morphological anomalies developed into mammary tumors because only young animals were used (24). We recently showed that transgenic mice over-expressing Prl in the differentiating/lactating mammary gland developed various benign lesions from the age of approximately 1 year (25).…”