The prolactin receptor (PRLR) signals predominantly through the JAK2-STAT5 pathway regulating multiple physiological functions relating to fertility, lactation, and metabolism. However, the molecular pathology and role of PRLR mutations and signalling are incompletely defined, with progress hampered by a lack of reported disease-associated PRLR variants. To date, two common germline PRLR variants are reported to demonstrate constitutive activity, with one, Ile146Leu, overrepresented in benign breast disease, while a rare activating variant, Asn492Ile, is reported to be associated with an increased incidence of prolactinoma. In contrast, an inactivating germline heterozygous PRLR variant (His188Arg) was reported in a kindred with hyperprolactinaemia, while an inactivating compound heterozygous PRLR variant (Pro269Leu/Arg171Stop) was identified in an individual with hyperprolactinaemia and agalactia. We hypothesised that additional rare germline PRLR variants, identified from large-scale sequencing projects (ExAC and GnomAD), may be associated with altered in vitro PRLR signalling activity. We therefore evaluated >300 previously uncharacterised non-synonymous, germline PRLR variants and selected 10 variants for in vitro analysis based on protein prediction algorithms, proximity to known functional domains and structural modelling. Five variants, including extracellular and intracellular domain variants, were associated with altered responses when compared to the wild-type receptor. These altered responses included loss- and gain-of-function activities related to STAT5 signalling, Akt and FOXO1 activity, as well as cell viability and apoptosis. These studies provide further insight into PRLR structure–function and indicate that rare germline PRLR variants may have diverse modulating effects on PRLR signalling, although the pathophysiologic relevance of such alterations remains to be defined.

催乳素受体 (PRLR) 主要通过 JAK2-STAT5 通路发出信号，调节与生育、哺乳和代谢相关的多种生理功能。然而，PRLR 突变和信号传导的分子病理学和作用尚未完全确定，由于缺乏与疾病相关的 PRLR 变异的报道，阻碍了进展。迄今为止，据报道，两种常见的种系PRLR变体表现出组成性活性，其中一种 Ile146Leu 在良性乳腺疾病中出现过多，而一种罕见的激活变体 Asn492Ile 据报道与催乳素瘤发病率增加有关。相比之下，在患有高泌乳素血症的亲属中报告了失活种系杂合PRLR变异（His188Arg），而在患有高泌乳素血症和无乳症的个体中发现了失活复合杂合PRLR变异（Pro269Leu/Arg171Stop）。我们假设从大规模测序项目（ExAC 和 GnomAD）中鉴定出的其他罕见种系PRLR变异可能与体外PRLR 信号活性的改变有关。因此，我们评估了超过 300 个先前未表征的非同义种系PRLR变体，并根据蛋白质预测算法、与已知功能域的接近度和结构建模选择了 10 个变体进行体外分析。与野生型受体相比，五种变体，包括胞外和胞内结构域变体，与反应改变相关。这些改变的反应包括与 STAT5 信号传导、Akt 和 FOXO1 活性相关的功能丧失和获得，以及细胞活力和凋亡。这些研究提供了对 PRLR 结构-功能的进一步了解，并表明罕见的种系PRLR变异可能对 PRLR 信号传导具有不同的调节作用，尽管此类改变的病理生理学相关性仍有待确定。