Mechanistic aspects of crosstalk between GH and PRL and ErbB receptor family signaling

Elucidation of the genetic determination of clutch traits in Chinese local chickens of the Laiwu Black breed

BACKGROUND

Egg laying rate (LR) is associated with a clutch, which is defined as consecutive days of oviposition. The clutch trait can be used as a selection indicator to improve egg production in poultry breeding. However, little is known about the genetic basis of clutch traits. In this study, our aim was to estimate genetic parameters and identify quantitative trait single nucleotide polymorphisms for clutch traits in 399 purebred Laiwu Black chickens (a native Chinese breed) using a genome-wide association study (GWAS).

METHODS

In this work, after estimating the genetic parameters of age at first egg, body weight at first egg, LR, longest clutch until 52 week of age, first week when the longest clutch starts, last week when the longest clutch ends, number of clutches, and longest number of days without egg-laying until 52 week of age, we identified single nucleotide polymorphisms (SNPs) and potential candidate genes associated with clutch traits in Laiwu Black chickens. The restricted maximum likelihood method was used to estimate genetic parameters of clutch pattern in 399 Laiwu Black hens, using the GCTA software.

RESULTS

The results showed that SNP-based heritability estimates of clutch traits ranged from 0.06 to 0.59. Genotyping data were obtained from whole genome re-sequencing data. After quality control, a total of 10,810,544 SNPs remained to be analyzed. The GWAS revealed that 421 significant SNPs responsible for clutch traits were scattered on chicken chromosomes 1-14, 17-19, 21-25, 28 and Z. Among the annotated genes, NELL2, SMYD9, SPTLC2, SMYD3 and PLCL1 were the most promising candidates for clutch traits in Laiwu Black chickens.

CONCLUSION

The findings of this research provide critical insight into the genetic basis of clutch traits. These results contribute to the identification of candidate genes and variants. Genes and SNPs potentially provide new avenues for further research and would help to establish a framework for new methods of genomic prediction, and increase the accuracy of estimated genetic merit for egg production and clutch traits.

The Mammary Gland: Basic Structure and Molecular Signaling during Development

The mammary gland is a compound, branched tubuloalveolar structure and a major characteristic of mammals. The mammary gland has evolved from epidermal apocrine glands, the skin glands as an accessory reproductive organ to support postnatal survival of offspring by producing milk as a source of nutrition. The mammary gland development begins during embryogenesis as a rudimentary structure that grows into an elementary branched ductal tree and is embedded in one end of a larger mammary fat pad at birth. At the onset of ovarian function at puberty, the rudimentary ductal system undergoes dramatic morphogenetic change with ductal elongation and branching. During pregnancy, the alveolar differentiation and tertiary branching are completed, and during lactation, the mature milk-producing glands eventually develop. The early stages of mammary development are hormonal independent, whereas during puberty and pregnancy, mammary gland development is hormonal dependent. We highlight the current understanding of molecular regulators involved during different stages of mammary gland development.

Prolactin: The Third Hormone in Breast Cancer

Prolactin coordinates with the ovarian steroids to orchestrate mammary development and lactation, culminating in nourishment and an increasingly appreciated array of other benefits for neonates. Its central activities in mammary epithelial growth and differentiation suggest that it plays a role(s) in breast cancer, but it has been challenging to identify its contributions, essential for incorporation into prevention and treatment approaches. Large prospective epidemiologic studies have linked higher prolactin exposure to increased risk, particularly for ER+ breast cancer in postmenopausal women. However, it has been more difficult to determine its actions and clinical consequences in established tumors. Here we review experimental data implicating multiple mechanisms by which prolactin may increase the risk of breast cancer. We then consider the evidence for role(s) of prolactin and its downstream signaling cascades in disease progression and treatment responses, and discuss how new approaches are beginning to illuminate the biology behind the seemingly conflicting epidemiologic and experimental studies of prolactin actions across diverse breast cancers.

Crosstalk between PRLR and EGFR/HER2 Signaling Pathways in Breast Cancer

Prolactin receptor (PRLR) and epidermal growth factor receptor (EGFR/ERBB) signaling pathways activated by prolactin (PRL) and epidermal growth factor (EGF), have a major role in the mammary gland development and in the etiology of breast cancer, respectively. ER+ breast tumors comprise up to 75% of all breast cancers and 10% of these are HER2+. Elevated levels of PRLR in breast tumors, high circulating levels of PRL and increased expression of ERBB1/2 in patients that become resistant to endocrine therapy have shown to be associated with higher risk of cancer progression. In this review, we examine the role of crosstalk between PRLR and ERBB1/2 signaling pathways in the activation of unliganded ERα, cyclin-D1 and other oncogenic factors (MYC, FOS, JUN) in breast cancer. PRL/PRLR and EGF/EGFR induces phosphorylation of ERα through activation of MEK/MAPK and PI3K/AKT signaling pathways. PRL in breast cancer cells via PRLR/JAK2 can also induce phosphorylation of ERBB2/HER2, which in turn activates the downstream RAS/MEK/ERK pathway required for ERα phosphorylation. EGFR, independent of PRL/PRLR, can activate STAT5 indirectly via c-SRC and drive the expression of target genes involved in cell proliferation and survival. The crosstalk between PRLR and HER2, where PRL induces HER2 signaling can be an alternative route for ERα activation to induce transcription of PRLR and other ER target genes. We believe that overexpression of EGFR/HER2 and PRLR in breast tumors could maximize the actions of their ligands, and further induce cell proliferation promoting malignancy. This could also explain the resistance to endocrine therapy resulting in tumor growth.

Pituitary Actions of EGF on Gonadotropins, Growth Hormone, Prolactin and Somatolactins in Grass Carp

Simple Summary

In mammals, the functions of epidermal growth factor (EGF) have been widely studied. However, little is known about the pituitary actions of EGF in teleost. Using primary cultured grass carp pituitary cells as model, we found that EGF could reduce pituitary luteinizing hormone β (LHβ) mRNA expression, but induce pituitary growth hormone (GH), prolactin (PRL) and somatolactins (SL) mRNA expression. Furthermore, we also found that NKB could suppress EGF-induced PRL mRNA expression in grass carp pituitary cells. These results suggested that EGF could directly regulate pituitary hormones expression in teleost.

Abstract

In mammals, epidermal growth factor (EGF) plays a vital role in both pituitary physiology and pathology. However, the functional role of EGF in the regulation of pituitary hormones has rarely reported in teleost. In our study, using primary cultured grass carp pituitary cells as an in vitro model, we examined the effects of EGF on pituitary hormone secretion and gene expression as well as the post-receptor signaling mechanisms involved. Firstly, we found that EGF significantly reduced luteinizing hormone (LHβ) mRNA expression via ErbB1 coupled to ERK1/2 pathway, but had no effect on LH release in grass carp pituitary cells. Secondly, the results showed that EGF was effective in up-regulating mRNA expression of growth hormone (GH), somatolactin α (SLα) and somatolactin β (SLβ) via ErbB1 and ErbB2 and subsequently coupled to MEK1/2/ERK1/2 and PI3K/Akt/mTOR pathways, respectively. However, EGF was not effective in GH release in pituitary cells. Thirdly, we found that EGF strongly induced pituitary prolactin (PRL) release and mRNA expression, which was mediated by ErbB1 and subsequent stimulation of MEK1/2/ERK1/2 and PI3K/Akt/mTOR pathways. Interestingly, subsequent study further found that neurokinin B (NKB) significantly suppressed EGF-induced PRL mRNA expression, which was mediated by neurokinin receptor (NK2R) and coupled to AC/cAMP/PKA signal pathway. These results suggested that EGF could differently regulate the pituitary hormones expression in grass carp pituitary cells.

WNT4 mediates the autocrine effects of growth hormone in mammary carcinoma cells

The expression of Wingless and Int-related protein (Wnt) ligands is aberrantly high in human breast cancer. We report here that WNT4 is significantly upregulated at the mRNA and protein level in mammary carcinoma cells expressing autocrine human growth hormone (hGH). Depletion of WNT4 using small interfering (si) RNA markedly decreased the rate of human breast cancer cell proliferation induced by autocrine hGH. Forced expression of WNT4 in the nonmalignant human mammary epithelial cell line MCF-12A stimulated cell proliferation in low and normal serum conditions, enhanced cell survival and promoted anchorage-independent growth and colony formation in soft agar. The effects of sustained production of WNT4 were concomitant with upregulation of proliferative markers (c-Myc, Cyclin D1), the survival marker BCL-XL, the putative WNT4 receptor FZD6 and activation of ERK1 and STAT3. Forced expression of WNT4 resulted in phenotypic conversion of MCF-12A cells, such that they exhibited the molecular and morphological characteristics of mesenchymal cells with increased cell motility. WNT4 production resulted in increased mesenchymal and cytoskeletal remodeling markers, promoted actin cytoskeleton reorganization and led to dissolution of cell-cell contacts. In xenograft studies, tumors with autocrine hGH expressed higher levels of WNT4 and FZD6 when compared with control tumors. In addition, Oncomine data indicated that WNT4 expression is increased in neoplastic compared with normal human breast tissue. Accordingly, immunohistochemical detection of WNT4 in human breast cancer biopsies revealed higher expression in tumor tissue vs normal breast epithelium. WNT4 is thus an autocrine hGH-regulated gene involved in the growth and development of the tumorigenic phenotype.

EGFR signaling promotes β-cell proliferation and survivin expression during pregnancy

Placental lactogen (PL) induced serotonergic signaling is essential for gestational β-cell mass expansion. We have previously shown that intact Epidermal growth factor –receptor (EGFR) function is a crucial component of this pathway. We now explored more specifically the link between EGFR and pregnancy-induced β-cell mass compensation. Islets were isolated from wild-type and β-cell-specific EGFR-dominant negative mice (E1-DN), stimulated with PL and analyzed for β-cell proliferation and expression of genes involved in gestational β-cell growth. β-cell mass dynamics were analyzed both with traditional morphometrical methods and three-dimensional optical projection tomography (OPT) of whole-mount insulin-stained pancreata. Insulin-positive volume analyzed with OPT increased 1.4-fold at gestational day 18.5 (GD18.5) when compared to non-pregnant mice. Number of islets peaked by GD13.5 (680 vs 1134 islets per pancreas, non-pregnant vs. GD13.5). PL stimulated beta cell proliferation in the wild-type islets, whereas the proliferative response was absent in the E1-DN mouse islets. Serotonin synthesizing enzymes were upregulated similarly in both the wild-type and E1-DN mice. However, while survivin (Birc5) mRNA was upregulated 5.5-fold during pregnancy in the wild-type islets, no change was seen in the E1-DN pregnant islets. PL induced survivin expression also in isolated islets and this was blocked by EGFR inhibitor gefitinib, mTOR inhibitor rapamycin and MEK inhibitor PD0325901. Our 3D-volumetric analysis of β-cell mass expansion during murine pregnancy revealed that islet number increases during pregnancy. In addition, our results suggest that EGFR signaling is required for lactogen-induced survivin expression via MAPK and mTOR pathways.

Hope and fear for interferon: the receptor-centric outlook on the future of interferon therapy

After several decades of intense clinical research, the great promise of Type I interferons (IFN1) as the anticancer wonder drugs that could cure or, at the very least, curb the progression of various oncological diseases has regrettably failed to deliver. Severe side effects and low efficacy of IFN1-based pharmaceutics greatly limited use of these drugs and further reduced the enthusiasm of clinical oncologists for future optimization of IFN1-based therapeutic modalities. Incredibly, extensive clinical studies to assess the efficacy of IFN1 alone or in combination with other anticancer drugs have not been paralleled by an equal scope in defining the determinants that confer cell sensitivity or refractoriness to IFN1. Given that all effects of IFN1 on malignant and benign cells alike are mediated by its receptor, the mechanisms regulating these receptor cell surface levels should play a paramount role in shaping the magnitude and duration of IFN1-elicited effects. These mechanisms and their role in controlling IFN1 responses, as well as an ability of a growing tumor to commandeer these events, are the focus of our review. We postulate that activation of numerous signaling pathways leading to elimination of IFN1 receptor occurs in cancer cells and benign cells that contribute to tumor tissue. We further hypothesize that activation of these eliminative pathways enables the escape from IFN1-driven suppression of tumorigenesis and elicits the primary refractoriness of tumor to the pharmaceutical IFN1.

GH mediates exercise-dependent activation of SVZ neural precursor cells in aged mice

Here we demonstrate, both in vivo and in vitro, that growth hormone (GH) mediates precursor cell activation in the subventricular zone (SVZ) of the aged (12-month-old) brain following exercise, and that GH signaling stimulates precursor activation to a similar extent to exercise. Our results reveal that both addition of GH in culture and direct intracerebroventricular infusion of GH stimulate neural precursor cells in the aged brain. In contrast, no increase in neurosphere numbers was observed in GH receptor null animals following exercise. Continuous infusion of a GH antagonist into the lateral ventricle of wild-type animals completely abolished the exercise-induced increase in neural precursor cell number. Given that the aged brain does not recover well after injury, we investigated the direct effect of exercise and GH on neural precursor cell activation following irradiation. This revealed that physical exercise as well as infusion of GH promoted repopulation of neural precursor cells in irradiated aged animals. Conversely, infusion of a GH antagonist during exercise prevented recovery of precursor cells in the SVZ following irradiation.

Stromal-epithelial interactions modulate cross-talk between prolactin receptor and HER2/Neu in breast cancer

Prolactin (PRL) promotes the proliferation and survival of breast cancer cells in part via the transactivation of human epidermal growth factor receptor 2 (HER2), also known as Neu in rodents. A PRL receptor (PRLR) antagonist, G129R, has been developed, which indirectly inhibits the tyrosine phosphorylation of HER2 (p-HER2) in human breast cancer cell lines. In this study, we investigate the effects of cancer-associated fibroblasts (CAFs) upon this molecular cross-talk using tumor cells and CAFs derived from spontaneous mammary tumors of female MMTV-neu transgenic mice. Tumors were resected and cultured as small tumor chunks (~3 mm3) or were cultured in monolayer. G129R reduced tyrosine phosphorylation of Neu (p-Neu) in a dose-dependent manner (IC50~10 μg/ml) in tumor chunks, but had no effect on primary tumor epithelial cells grown in monolayer. Direct co-culture of mouse or human tumor epithelial cell lines with CAFs restored the epithelial cells' response to G129R, similar to that observed in mouse tumor chunks. The addition of PRL, as expected, induced p-Neu in both the tumor chunk and co-culture models. The inhibitory effect of G129R was absent when CAFs were physically separated from mouse tumor epithelial cells using a transwell system, or when CAFs were replaced with normal fibroblasts in direct co-culture with human or mouse tumor epithelial cells. In vivo, G129R reduced p-Neu levels in primary mammary tumors of mice in a time- and dose-dependent manner. In conclusion, CAFs play a critical role in bridging the cross-talk between PRL and HER2/Neu in both mouse and human models of breast cancer. The inhibitory effects of G129R on p-Neu and on tumor growth are dependent upon interactions of tumor epithelial cells with CAFs.

Role of the growth hormone-IGF-1 axis in cancer

A substantial body of evidence supports a role for the growth hormone (GH)-IGF-1 axis in cancer incidence and progression. This includes epidemiological evidence relating elevated plasma IGF-1 to cancer incidence as well as a lack of cancers in GH/IGF-1 deficiency. Rodent models lacking GH or its receptor are strikingly resistant to the induction of a wide range of cancers, and treatment with the GH antagonist pegvisomant slows tumor progression. While GH receptor expression is elevated in many cancers, autocrine GH is present in several types, and overexpression of autocrine GH can induce cell transformation. While the mechanism of autocrine action is not clear, it does involve both STAT5 and STAT3 activation, and probably nuclear translocation of the GH receptor. Development of a more potent GH receptor antagonist or secretion inhibitor is warranted for cancer therapy.

Complex prolactin crosstalk in breast cancer: new therapeutic implications

The contributions of prolactin (PRL) to breast cancer are becoming increasingly recognized. To better understand the role for PRL in this disease, its interactions with other oncogenic growth factors and hormones must be characterized. Here, we review our current understanding of PRL crosstalk with other mammary oncogenic factors, including estrogen, epidermal growth factor (EGF) family members, and insulin-like growth factor-I (IGF-I). The ability of PRL to potentiate the actions of these targets of highly successful endocrine and molecular therapies suggests that PRL and/or its receptor (PRLR) may be an attractive therapeutic target(s). We discuss the potential benefit of PRL/PRLR-targeted therapy in combination with established therapies and implications for de novo and acquired resistance to treatment.

Growth hormone and insulin-like growth factor-I in the transition from normal mammary development to preneoplastic mammary lesions

Adult female mammary development starts at puberty and is controlled by tightly regulated cross-talk between a group of hormones and growth factors. Although estrogen is the initial driving force and is joined by luteal phase progesterone, both of these hormones require GH-induced IGF-I in the mammary gland in order to act. The same group of hormones, when experimentally perturbed, can lead to development of hyperplastic lesions and increase the chances, or be precursors, of mammary carcinoma. For example, systemic administration of GH or IGF-I causes mammary hyperplasia, and overproduction of IGF-I in transgenic animals can cause the development of usual or atypical hyperplasias and sometimes carcinoma. Although studies have clearly demonstrated the transforming potential of both GH and IGF-I receptor in cell culture and in animals, debate remains as to whether their main role is actually instructive or permissive in progression to cancer in vivo. Genetic imprinting has been shown to occur in precursor lesions as early as atypical hyperplasia in women. Thus, the concept of progression from normal development to cancer through precursor lesions sensitive to hormones and growth factors discussed above is gaining support in humans as well as in animal models. Indeed, elevation of estrogen receptor, GH, IGF-I, and IGF-I receptor during progression suggests a role for these pathways in this process. New agents targeting the GH/IGF-I axis may provide a novel means to block formation and progression of precursor lesions to overt carcinoma. A novel somatostatin analog has recently been shown to prevent mammary development in rats via targeted IGF-I action inhibition at the mammary gland. Similarly, pegvisomant, a GH antagonist, and other IGF-I antagonists such as IGF binding proteins 1 and 5 also block mammary gland development. It is, therefore, possible that inhibition of IGF-I action, or perhaps GH, in the mammary gland may eventually play a role in breast cancer chemoprevention by preventing actions of both estrogen and progesterone, especially in women at extremely high risk for developing breast cancer such as BRCA gene 1 or 2 mutations.