Prolactin Receptor in Primary Hyperparathyroidism – Expression, Functionality and Clinical Correlations

<div><h3>Background</h3><p>Primary hyperparathyroidism (PHPT) is an endocrine disorder most commonly affecting women, suggesting a role for female hormones and/or their receptors in parathyroid adenomas. We here investigated the prolactin receptor (PRLr) which is associated with tumours of the breast and other organs.</p> <h3>Methodology/Principal Findings</h3><p>PRLr expression was investigated in a panel of 37 patients with sporadic parathyroid tumours and its functionality in cultured parathyroid tumour cells. In comparison with other tissues and breast cancer cells, high levels of prolactin receptor gene (<em>PRLR</em>) transcripts were demonstrated in parathyroid tissues. PRLr products of 60/70 kDa were highly expressed in all parathyroid tumours. In addition varying levels of the 80 kDa PRLr isoform, with known proliferative activity, were demonstrated. In parathyroid tumours, PRLr immunoreactivity was observed in the cytoplasm (in all cases, n = 36), cytoplasmic granulae (n = 16), the plasma membrane (n = 12) or enlarged lysosomes (n = 4). In normal parathyroid rim (n = 28), PRLr was uniformly expressed in the cytoplasm and granulae. In <em>in vitro</em> studies of short-term cultured human parathyroid tumour cells, prolactin stimulation was associated with significant transcriptional changes in JAK/STAT, RIG-I like receptor and type II interferon signalling pathways as documented by gene expression profiling. Moreover, <em>PRLR</em> gene expression in parathyroid tumours was inversely correlated with the patients’ plasma calcium levels.</p> <h3>Conclusions</h3><p>We demonstrate that the prolactin receptor is highly abundant in human parathyroid tissues and that PRLr isoforms expression and PRLr subcellular localisation are altered in parathyroid tumours. Responsiveness of PRLr to physiological levels of prolactin was observed in the form of increased PTH secretion and altered gene transcription with significant increase of RIG-I like receptor, JAK-STAT and Type II interferon signalling pathways. These data suggest a role of the prolactin receptor in parathyroid adenomas.</p> </div

Immunohistochemical analysis of PRLr expression using the PRLrI antibody

<p>. The photomicrographs show parathyroid tumour tissues (A–C) and negative control (D). Parathyroid tumours are shown with immunostaining of cytoplasmic granulae and cytoplasm (A), of cytoplasm only (B), and of cell membrane and cytoplasm (C).</p

Western blot analysis of protein expression for GSK3β and isoforms of the prolactin receptor.

<p>A) Detection of 80 kDa and 60/70 kDa products with the PRLrI antibody in normal tissues, T47D cells and parathyroid tumours, and 60/70 kDa N-glycosylated PRLr products with the gPRLr antibody in parathyroid tumours. B) Expression of total GSK3β (left) as well as Ser9-phosphorylated GSK3β (right) in parathyroid tumours and normal tissue.</p

Localisation of PRLr expression to lysosomes in normal parathyroid rim and to enlarged lysosomes in parathyroid tumour tissue.

<p>A) Immunohistochemistry with PRLrI showing “ring-like” cytoplasmic structures and cytoplasmic reactivity. B) Immunohistochemistry of PRLrI showing cytoplasmic granuale and cytoplasmic reactivty. C and D) Analysis of “ring like” structures and cytoplasmic granulae by flourescent immunohistochemistry. Images show one parathyroid tumour (C) and normal parathyroid rim (D), stained with DAPI (blue), anti-PRLrI (red, upper right) and anti-SCARB2 (green lysosomal marker, lower left) separately and in overlay (lower right and upper left).</p

Clustering and PCA analysis of differentially expressed genes after prolactin treatment in parathyroid adenoma cells.

<p>A) Heat map of hierarchical clustering show 58 changed genes (adjusted P<0.01) as detected by Qlucore analysis. B) PCA of the gene expression data in a 2D graph, plotting individual primary cultures of parathyroid adenomas. Colours indicate either; green = control or red = prolactin treated. Numbers indicate individual cases. For significant genes (adjusted P<0.01), samples were grouped according to treatment. Lines indicate the three closest relationships to a sample.</p

qRT-PCR analysis for <i>PRLR</i> expression in normal parathyroid tissue and parathyroid tumours.

<p>Box-plots show<i>PRLR</i>-total mRNA expression after normalization in normal parathyroid tissue and parathyroid tumours (A), and normal parathyroid and other normal tissues (B). The arbitrary value of 1.0 indicating the expression level in MCF-7 cells is indicated.</p

Analysis of PTH secretion and intracellular Ca²⁺ after prolactin treatment.

<p>A) Measurements of PTH secretion from parathyroid adenoma cells upon treatments with prolactin at 100 µg/L or 200 µg/L. Results from four independent experiments are shown. B) Example of a measurement of intracellular Ca²⁺ in parathyroid adenoma cells treated with 100 µg/L followed by 200 µg/L prolactin, as indicated by vertical red lines.</p

Pathways with enrichment of dysregulated genes.

<p>Pathways with enrichment of dysregulated genes.</p