Breast Cancer and Prolactin - New Mechanisms and Models

Identification of key genes linking bisphenols exposure and breast cancer

Breast cancer (BC) is one of the most common types of cancer and is caused by the complex interplay of genetic and environmental factors, such as an unhealthy lifestyle, family history of illness, reproductive factors, and ageing. However, increasing evidence has revealed that manufactured organic pollutants such as bisphenols are closely related to BC. Bisphenols exposure can promote the progression of BC through multiple complicated and variable molecular mechanisms. Reanalysis of existing data on this topic may reveal molecular markers with clinical value. In this study, we identified four key genes [keratin 14 (KRT14), keratin 5 (KRT5), acyl-CoA synthetase long chain family member 1 (ACSL1) and matrix metallopeptidase 1 (MMP1)] related to both bisphenols exposure and BC by employing the Comparative Toxicogenomics Database (CTD) and The Cancer Genome Atlas Cervical Cancer (TCGA-CESC) dataset; notably, KRT14 expression exhibited the most significant difference between tumour and normal tissues. Further analysis of the functions and biological processes associated with KRT14 and related regulatory molecules revealed that bisphenols exposure induces BC-promoting characteristics and aggressive behaviour-related signaling pathways, such as the steroid biosynthesis, Forkhead box (FOXO) and prolactin signaling pathways. To confirm the expression and biological effects of KRT14, we conducted relevant experiments. In vitro studies revealed that bisphenols such as bisphenol A (BPA) exposure significantly affected the proliferation, migration, and invasion of MCF-7 cells by inhibiting KRT14 expression. Similarly, we also observed a decrease in KRT14 expression in BPA induced abnormal breast tissue in mice. In summary, our study revealed potential genes and pathways associated with bisphenols exposure in BC.

Growth Hormone Action as a Target in Cancer: Significance, Mechanisms, and Possible Therapies

Growth hormone (GH) is a pituitary-derived endocrine hormone required for normal postnatal growth and development. Hypo- or hypersecretion of endocrine GH results in 2 pathologic conditions, namely GH deficiency (GHD) and acromegaly. Additionally, GH is also produced in nonpituitary and tumoral tissues, where it acts rather as a cellular growth factor with an autocrine/paracrine mode of action. An increasingly persuasive and large body of evidence over the last 70 years concurs that GH action is implicit in escalating several cancer-associated events, locally and systemically. This pleiotropy of GH's effects is puzzling, but the association with cancer risk automatically raises a concern for patients with acromegaly and for individuals treated with GH. By careful assessment of the available knowledge on the fundamental concepts of cancer, suggestions from epidemiological and clinical studies, and the evidence from specific reports, in this review we aimed to help clarify the distinction of endocrine vs autocrine/paracrine GH in promoting cancer and to reconcile the discrepancies between experimental and clinical data. Along this discourse, we critically weigh the targetability of GH action in cancer-first by detailing the molecular mechanisms which posit GH as a critical node in tumor circuitry; and second, by enumerating the currently available therapeutic options targeting GH action. On the basis of our discussion, we infer that a targeted intervention on GH action in the appropriate patient population can benefit a sizable subset of current cancer prognoses.

Breast Cancer risk in patients with dopamine agonist-treated hyperprolactinemia

PURPOSE

Given prolactin's (PRL) multifaceted roles in mammary tissue, an association between hyperprolactinemia and breast cancer has been hypothesized. Despite previous studies not identifying this risk, we aimed to investigate whether a connection exists.

METHODS

This retrospective cohort study compared breast cancer incidence in patients with dopamine agonist (DA)-treated hyperprolactinemia versus matched controls in a 1:5 ratio. The primary outcome was a breast cancer diagnosis following hyperprolactinemia diagnosis.

RESULTS

The cohort consisted of 1484 female patients with DA-treated hyperprolactinemia matched to 7418 female controls (mean age at diagnosis 32.70 ± 11.12 years; BMI 25.60 ± 5.84 kg/m2). Breast cancer was diagnosed in 27 patients with hyperprolactinemia (1.82%) and 97 controls (1.31%) (HR 1.40, 95% CI 0.91-2.14, p = 0.12). Patients who developed breast cancer were diagnosed with hyperprolactinemia later in life than those who did not (median age 42.63 vs. 29.79 years; p < 0.0001). Patients with PRL < 5× upper limit of normal (ULN) at diagnosis developed breast cancer at a higher rate than controls (2.25% vs. 1.33%; HR 1.73, 95% CI 1.09-2.75), but the difference was not significant in patients with PRL ≥ 5×ULN. Patients who exhibited longer times to PRL normalization had higher incidence of breast cancer (median 2.60 vs. 1.41 years in those who did not develop breast cancer; p = 0.03).

CONCLUSION

Overall, patients with DA-treated hyperprolactinemia did not show an increased risk for breast cancer compared to controls. However, the risk was significantly higher among those whose PRL levels were < 5×ULN, had advanced age of diagnosis, or prolonged time to PRL normalization.

Simultaneous Detection of Prolactin and Growth Hormone Using a Dual-label Time-resolved Fluorescence Immunoassay

Prolactin (PRL) and growth hormone (GH) are two important hormones secreted by the pituitary gland, and their abnormal levels are often related to disease status. This study aimed to establish a new dual-label time-resolved fluorescence immunoassay (TRFIA) to quantitatively measure PRL and GH levels in serum. A sandwich TRFIA was optimized and established: anti-PRL/GH antibodies immobilized on 96-well plates captured PRL/GH and then banded together with anti-PRL/GH paired antibodies labeled with europium(III) (Eu3+)/samarium(III) (Sm3+) chelates. Finally, a time-resolved analyzer measured the Eu3+/Sm3+ fluorescence values. Clinical serum samples were used to evaluate the detection performance of this method. The sensitivities of this dual-label TRFIA were 0.35 ng/mL and 0.45 ng/mL, respectively, and the detection range was between 0.1 and 1000 ng/mL. All the cross-reactivities were lower than 1.07%. The intra-assay and interassay coefficients of variation were 2.18-7.85% and 2.25-7.30%, respectively. Compared with the registered TRFIA kits, a high Pearson coefficient (r = 0.9626 and 0.9675) was observed. This dual-label TRFIA has high sensitivity, accuracy and specificity with good clinical detection performance, representing a suitable alternative to existing methods for determining PRL and GH levels, and is expected to be used in the clinic in the future.

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.