Breast Cancer and Prolactin - New Mechanisms and Models

Prolactin: structure, receptors, and functions

Prolactin (PRL) is a 23-kDa protein synthesized and secreted by lactotroph cells of the anterior pituitary gland but also by other peripheral tissues. PRL binds directly to a unique transmembrane receptor (PRLR), and the JAK2/signal transducer and activator of transcription 5 (Stat5) pathway is considered the major downstream pathway for PRLR signaling. To a lesser extent, PRL may be cleaved into the shorter 16-kDa PRL, also called vasoinhibin, whose signaling is not fully known. According to rodent models of PRL signaling inactivation and the identification of human genetic alterations in PRL signaling, a growing number of biological processes are partly mediated by PRL or its downstream effectors. In this review, we focused on PRL structure and signaling and its canonical function in reproduction. In addition to regulating reproductive functions, PRL also plays a role in behavior, notably in initiating nurturing and maternal behavior. We also included recent insights into PRL function in several fields, including migraines, metabolic homeostasis, inflammatory and autoimmune disease, and cancer. Despite the complexity of understanding the many functions of PRL, new research in this field offers interesting perspectives on physiological and pathophysiological processes.

Therapeutic strategies for colorectal cancer: antitumor efficacy of dopamine D2 receptor antagonists

Colorectal cancer (CRC) is one of the leading causes of death, accounting for more than half a million deaths annually. Even worse, an increasing number of cancer cases are diagnosed yearly, and two and a half million new cancer cases are estimated to be diagnosed in 2035. Some antipsychotic drugs, especially those targeting dopamine receptor (DR) D2, demonstrated anticancer activity. Studies have revealed the potential of DRD2 antagonists as anticancer therapeutics, whether alone or as an adjuvant, in treating breast cancer, lung cancer, and others. Emerging evidences indicate DRD2 is involved in the CRC biology, and the association between DRD2 and CRC could be utilized in treating CRC. This study selected DRD2 antagonists with anticancer activity to elucidate the possibility of DRD2 antagonists as new therapeutics for treating CRC.

Prolactin-activated PAK1 potentiates estrogen response to breast cancer cell epithelial-mesenchymal transition, migration and invasion

Hormones estrogen and prolactin exert independent effects on breast cancer while their crosstalk synergistically enhance breast cancer cell proliferation. We have previously shown that the serine/threonine kinase PAK1 is responsible for this effect and proposed the mechanism of PAK1 action. Here we extended our previous data to demonstrate that the PAK1 kinase is a common interplay in PRL and E2 crosstalk to regulate epithelial-mesenchymal transition, cell migration and invasiveness of human breast cancer cells.

Prolactin-induced tyrosyl phosphorylation of PAK1 facilitates epithelial-mesenchymal transition

PAK1 and prolactin (PRL) regulate breast cancer. Prolactin-activated JAK2 tyrosyl phosphorylates PAK1 (pTyr-PAK1). We demonstrate here that pTyr-PAK1 regulates epithelial-mesenchymal transition (EMT) in breast cancer cells. PRL treatment of T47D PAK1 WT cells leads to downregulation of E-cadherin surface expression and "ectodomain shedding" (extracellular cleavage of E-cadherin). pTyr-PAK1 increases mRNA levels of Snail, Slug, and Twist2, transcriptional factors implicated in E-cadherin repression. pTyr-PAK1 also significantly increases PRL-dependent Slug activity leading to expression of vimentin, a hallmark of EMT. Thus, our current data on pTyr-PAK1 regulation of EMT bring insight into the role of PAK1 and PRL in human breast cancer.

Current Insights in Prolactin Signaling and Ovulatory Function

Prolactin (PRL) is a pleiotropic hormone released from lactotrophic cells of the anterior pituitary gland that also originates from extrapituitary sources and plays an important role in regulating lactation in mammals, as well as other actions. Acting in an endocrine and paracrine/autocrine manner, PRL regulates the hypothalamic-pituitary-ovarian axis, thus influencing the maturation of ovarian follicles and ovulation. This review provides a detailed discussion of the current knowledge on the role of PRL in the context of ovulation and ovulatory disorders, particularly with regard to hyperprolactinemia, which is one of the most common causes of infertility in women. Much attention has been given to the PRL structure and the PRL receptor (PRLR), as well as the diverse functions of PRLR signaling under normal and pathological conditions. The hormonal regulation of the menstrual cycle in connection with folliculogenesis and ovulation, as well as the current classifications of ovulation disorders, are also described. Finally, the state of knowledge regarding the importance of TIDA (tuberoinfundibular dopamine), KNDγ (kisspeptin/neurokinin B/dynorphin), and GnRH (gonadotropin-releasing hormone) neurons in PRL- and kisspeptin (KP)-dependent regulation of the hypothalamic-pituitary-gonadal (HPG) axis in women is reviewed. Based on this review, a rationale for influencing PRL signaling pathways in therapeutic activities accompanying ovulation disorders is presented.

The relationship between antidepressants and breast cancer: evidence from Mendelian randomization

BACKGROUND

The use of antidepressants has increased over the years, but the relationship between antidepressant use and the risk of breast cancer is not uniform because of confounding factors. We aimed to assess the effect of antidepressants on breast cancer risk using a two-sample Mendelian randomization (MR) approach.stet METHODS: Secondary data analysis was performed on pooled data from genome-wide association studies based on single-nucleotide polymorphisms that were highly correlated with antidepressants, SSRI drugs, and serotonin and prolactin levels were selected as instrumental variables to evaluate the association between antidepressants and SSRI drugs and prolactin levels with breast cancer and ER+/ER- breast cancer. We then performed a test of the hypothesis that SSRI drugs elevate prolactin concentrations. We performed two-sample Mendelian randomization analyses using inverse variance weighting, MR-Egger regression, and weighted median methods, respectively.

RESULTS

There was no significant risk association between antidepressant and SSRI use and the development of breast cancer, ER-positive or ER-negative breast cancer (P > 0.05), and serotonin concentration was not associated with breast cancer risk (P > 0.05). There was a positive causal relationship between prolactin levels and breast cancer (IVW, P = 0.02, OR = 1.058) and ER-positive breast cancer (Weighted median, P = 0.043, OR = 1.141; IVW, P = 0.009, OR = 1.125). Results in SSRI medication and prolactin levels showed no association between SSRI analogs and prolactin levels (P > 0.05).

CONCLUSION

Large MR analysis showed that antidepressants as well as SSRI drugs were not associated with breast cancer risk and the SSRI-prolactin-breast cancer hypothesis did not hold in our analysis.

The prolactin receptor scaffolds Janus kinase 2 via co-structure formation with phosphoinositide-4,5-bisphosphate

Class 1 cytokine receptors transmit signals through the membrane by a single transmembrane helix to an intrinsically disordered cytoplasmic domain that lacks kinase activity. While specific binding to phosphoinositides has been reported for the prolactin receptor (PRLR), the role of lipids in PRLR signaling is unclear. Using an integrative approach combining nuclear magnetic resonance spectroscopy, cellular signaling experiments, computational modeling, and simulation, we demonstrate co-structure formation of the disordered intracellular domain of the human PRLR, the membrane constituent phosphoinositide-4,5-bisphosphate (PI(4,5)P2) and the FERM-SH2 domain of the Janus kinase 2 (JAK2). We find that the complex leads to accumulation of PI(4,5)P2 at the transmembrane helix interface and that the mutation of residues identified to interact specifically with PI(4,5)P2 negatively affects PRLR-mediated activation of signal transducer and activator of transcription 5 (STAT5). Facilitated by co-structure formation, the membrane-proximal disordered region arranges into an extended structure. We suggest that the co-structure formed between PRLR, JAK2, and PI(4,5)P2 locks the juxtamembrane disordered domain of the PRLR in an extended structure, enabling signal relay from the extracellular to the intracellular domain upon ligand binding. We find that the co-structure exists in different states which we speculate could be relevant for turning signaling on and off. Similar co-structures may be relevant for other non-receptor tyrosine kinases and their receptors.