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Deletion of the nuclear localization sequences and C-terminus of PTHrP impairs embryonic mammary development but also inhibits PTHrP production.

ABSTRACT: Parathyroid hormone-related protein (PTHrP) can be secreted from cells and interact with its receptor, the Type 1 PTH/PTHrP Receptor (PTHR1) in an autocrine, paracrine or endocrine fashion. PTHrP can also remain inside cells and be transported into the nucleus, where its functions are unclear, although recent experiments suggest that it may broadly regulate cell survival and senescence. Disruption of either the PTHrP or PTHR1 gene results in many abnormalities including a failure of embryonic mammary gland development in mice and in humans. In order to examine the potential functions of nuclear PTHrP in the breast, we examined mammary gland development in PTHrP (1-84) knock-in mice, which express a mutant form of PTHrP that lacks the C-terminus and nuclear localization signals and which can be secreted but cannot enter the nucleus. Interestingly, we found that PTHrP (1-84) knock-in mice had defects in mammary mesenchyme differentiation and mammary duct outgrowth that were nearly identical to those previously described in PTHrP-/- and PTHR1-/- mice. However, the mammary buds in PTHrP (1-84) knock-in mice had severe reductions in mutant PTHrP mRNA levels, suggesting that the developmental defects were due to insufficient production of PTHrP by mammary epithelial cells and not loss of PTHrP nuclear function. Examination of the effects of nuclear PTHrP in the mammary gland in vivo will require the development of alternative animal models.

SUBMITTER: Boras-Granic K

PROVIDER: S-EPMC4006745 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature

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Deletion of the nuclear localization sequences and C-terminus of PTHrP impairs embryonic mammary development but also inhibits PTHrP production.

Boras-Granic Kata K Dann Pamela P Vanhouten Joshua J Karaplis Andrew A Wysolmerski John J

PloS one 20140501 5

Parathyroid hormone-related protein (PTHrP) can be secreted from cells and interact with its receptor, the Type 1 PTH/PTHrP Receptor (PTHR1) in an autocrine, paracrine or endocrine fashion. PTHrP can also remain inside cells and be transported into the nucleus, where its functions are unclear, although recent experiments suggest that it may broadly regulate cell survival and senescence. Disruption of either the PTHrP or PTHR1 gene results in many abnormalities including a failure of embryonic ma ...[more]

PMID: 24785493

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Project description:BackgroundParathyroid hormone-related protein (PTHrP) is required for embryonic breast development and has important functions during lactation, when it is produced by alveolar epithelial cells and secreted into the maternal circulation to mobilize skeletal calcium used for milk production. PTHrP is also produced by breast cancers, and GWAS studies suggest that it influences breast cancer risk. However, the exact functions of PTHrP in breast cancer biology remain unsettled.MethodsWe developed a tetracycline-regulated, MMTV (mouse mammary tumor virus)-driven model of PTHrP overexpression in mammary epithelial cells (Tet-PTHrP mice) and bred these mice with the MMTV-PyMT (polyoma middle tumor-antigen) breast cancer model to analyze the impact of PTHrP overexpression on normal mammary gland biology and in breast cancer progression.ResultsOverexpression of PTHrP in luminal epithelial cells caused alveolar hyperplasia and secretory differentiation of the mammary epithelium with milk production. This was accompanied by activation of Stat5 and increased expression of E74-like factor-5 (Elf5) as well as a delay in post-lactation involution. In MMTV-PyMT mice, overexpression of PTHrP (Tet-PTHrP;PyMT mice) shortened tumor latency and accelerated tumor growth, ultimately reducing overall survival. Tumors overproducing PTHrP also displayed increased expression of nuclear pSTAT5 and Elf5, increased expression of markers of secretory differentiation and milk constituents, and histologically resembled secretory carcinomas of the breast. Overexpression of PTHrP within cells isolated from tumors, but not PTHrP exogenously added to cell culture media, led to activation of STAT5 and milk protein gene expression. In addition, neither ablating the Type 1 PTH/PTHrP receptor (PTH1R) in epithelial cells nor treating Tet-PTHrP;PyMT mice with an anti-PTH1R antibody prevented secretory differentiation or altered tumor latency. These data suggest that PTHrP acts in a cell-autonomous, intracrine manner. Finally, expression of PTHrP in human breast cancers is associated with expression of genes involved in milk production and STAT5 signaling.ConclusionsOur study suggests that PTHrP promotes pathways leading to secretory differentiation and proliferation in both normal mammary epithelial cells and in breast tumor cells.

Dataset Information

Deletion of the nuclear localization sequences and C-terminus of PTHrP impairs embryonic mammary development but also inhibits PTHrP production.

Publications

Deletion of the nuclear localization sequences and C-terminus of PTHrP impairs embryonic mammary development but also inhibits PTHrP production.

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