An Rb family-independent E2F3 transcription factor variant impairs STAT5 signaling and mammary gland remodeling during pregnancy in mice

Spatio-temporal transcriptome dynamics coordinate rapid transition of core crop functions in 'lactating' pigeon

Pigeons (Columba livia) are among a select few avian species that have developed a specialized reproductive mode wherein the parents produce a 'milk' in their crop to feed newborn squabs. Nonetheless, the transcriptomic dynamics and role in the rapid transition of core crop functions during 'lactation' remain largely unexplored. Here, we generated a de novo pigeon genome assembly to construct a high resolution spatio-temporal transcriptomic landscape of the crop epithelium across the entire breeding stage. This multi-omics analysis identified a set of 'lactation'-related genes involved in lipid and protein metabolism, which contribute to the rapid functional transitions in the crop. Analysis of in situ high-throughput chromatin conformation capture (Hi-C) sequencing revealed extensive reorganization of promoter-enhancer interactions linked to the dynamic expression of these 'lactation'-related genes between stages. Moreover, their expression is spatially localized in specific epithelial layers, and can be correlated with phenotypic changes in the crop. These results illustrate the preferential de novo synthesis of 'milk' lipids and proteins in the crop, and provides candidate enhancer loci for further investigation of the regulatory elements controlling pigeon 'lactation'.

Hormonal regulation of mammary gland development and lactation

Lactation is critical to infant short-term and long-term health and protects mothers from breast cancer, ovarian cancer and type 2 diabetes mellitus. The mammary gland is a dynamic organ, regulated by the coordinated actions of reproductive and metabolic hormones. These hormones promote gland development from puberty onwards and induce the formation of a branched, epithelial, milk-secreting organ by the end of pregnancy. Progesterone withdrawal following placental delivery initiates lactation, which is maintained by increased pituitary secretion of prolactin and oxytocin, and stimulated by infant suckling. After weaning, local cytokine production and decreased prolactin secretion trigger large-scale mammary cell loss, leading to gland involution. Here, we review advances in the molecular endocrinology of mammary gland development and milk synthesis. We discuss the hormonal functions of the mammary gland, including parathyroid hormone-related peptide secretion that stimulates maternal calcium mobilization for milk synthesis. We also consider the hormonal composition of human milk and its associated effects on infant health and development. Finally, we highlight endocrine and metabolic diseases that cause lactation insufficiency, for example, monogenic disorders of prolactin and prolactin receptor mutations, maternal obesity and diabetes mellitus, interventions during labour and delivery, and exposure to endocrine-disrupting chemicals such as polyfluoroalkyl substances in consumer products and other oestrogenic compounds.

Genistein Directly Represses the Phosphorylation of STAT5 in Lactating Mammary Epithelial Cells

Genistein is a soy isoflavone and shows various physiological activities, such as affinities for estrogen receptors (ERs) and inhibitory effects on the epidermal growth factor receptor (EGFR) pathway. A previous study reported that genistein downregulates milk production ability in mammary epithelial cells (MECs) while decreasing the phosphorylation of STAT5. The ER and EGFR pathways indirectly regulate STAT5. In this study, the repressing mechanism of genistein against the phosphorylation of STAT5 was investigated using a culture model of mouse MECs with milk production ability. The results revealed that genistein did not influence the behavior of ERα and ERβ, whereas genistein immediately repressed the phosphorylation of ERK1/2. However, the decrease in phosphorylated STAT5 occurred independent of the phosphorylation of EGFR. Genistein repressed new phosphorylation of STAT5 by prolactin without influencing the phosphorylation of JAK2. In conclusion, this study indicates that genistein directly inhibits the phosphorylation of STAT5 in lactating MECs.

NatB regulates Rb mutant cell death and tumor growth by modulating EGFR/MAPK signaling through the N-end rule pathways

Inactivation of the Rb tumor suppressor causes context-dependent increases in cell proliferation or cell death. In a genetic screen for factors that promoted Rb mutant cell death in Drosophila, we identified Psid, a regulatory subunit of N-terminal acetyltransferase B (NatB). We showed that NatB subunits were required for elevated EGFR/MAPK signaling and Rb mutant cell survival. We showed that NatB regulates the posttranscriptional levels of the highly conserved pathway components Grb2/Drk, MAPK, and PP2AC but not that of the less conserved Sprouty. Interestingly, NatB increased the levels of positive pathway components Grb2/Drk and MAPK while decreased the levels of negative pathway component PP2AC, which were mediated by the distinct N-end rule branch E3 ubiquitin ligases Ubr4 and Cnot4, respectively. These results suggest a novel mechanism by which NatB and N-end rule pathways modulate EGFR/MAPK signaling by inversely regulating the levels of multiple conserved positive and negative pathway components. As inactivation of Psid blocked EGFR signaling-dependent tumor growth, this study raises the possibility that NatB is potentially a novel therapeutic target for cancers dependent on deregulated EGFR/Ras signaling.

Rb family-independent activating E2F increases genome stability, promotes homologous recombination, and decreases non-homologous end joining

The retinoblastoma protein Rb is a prototype tumor suppressor inactivated in a variety of cancers. In addition to deregulated cell proliferation, Rb inactivation also causes genome instability that contributes to tumorigenesis. Although the genome instability effects of Rb inactivation was shown to be mediated mainly by E2F-independent mechanisms, little is known about whether the constitutive free activating E2F proteins released by Rb-inactivation affects genome stability. In this manuscript, we take advantage of the dE2F1^su89 mutant, which contains a point mutation in the conserved Rb-binding domain that disrupts its interaction with the Rb family proteins, to characterize the effect of constitutive free activating E2F on genome stability in the presence of WT Rb. We showed that dE2F1^su89 promoted genome stability in the mwh genome stability assay. We found that the genome stability effects of dE2F1^su89 was sensitive to the levels of activating E2F activity and to the levels of E2F targets involved in DNA replication and repair but not to the level of E2F cell cycle target Cyclin E. Importantly, we showed that dE2F1^su89 promoted DNA double-strand break (DSB) repair by homologous recombination and decreased DSB repair by Non-homologous end joining (NHEJ). These results show that the constitutive free activating E2F promotes genome stability, which potentially contributes the observed tumor development in E2F1 knockout mice and the reported NHEJ defects in Rb mutant cells. These results also explain why constitutive free activating E2F alone was not sufficient for tumor development.

Kp-10 promotes bovine mammary epithelial cell proliferation by activating GPR54 and its downstream signaling pathways

It has been reported that the proliferation and apoptosis of mammary epithelial cells affect milk production. Therefore, ensuring adequate mammary epithelial cells is expected to enhance milk production. This study is devoted to studying the effects of kisspeptin-10 (Kp-10), a peptide hormone composed of 10 amino acids, on bovine mammary epithelial cell (bMEC) proliferation and exploring the underlying mechanism of its action. bMECs were treated with various concentrations of Kp-10 (1, 10, 100, and 1,000 nM), and 100 nM Kp-10 promoted the proliferation of the bMECs. Kp-10 promoted the cell cycle transition from G1 to the S and G2 phases, increased the protein levels of Cyclin D1 and Cyclin D3, and reduced the expression levels of the p21 gene. This study also showed that inhibition of G protein-coupled receptor 54 (GPR54), AKT, mTOR, and ERK1/2 reduced the proliferation of the bMECs that had been induced by Kp-10. In addition, Kp-10 decreased the complexes formed by Rb and E2F1 and increased the expression levels of the E2F1 target genes. These results indicate that Kp-10 promotes bMEC proliferation by activating GPR54 and its downstream signaling pathways.

Ginseng metabolite Protopanaxadiol induces Sestrin2 expression and AMPK activation through GCN2 and PERK

Ginseng is one of the most commonly used herbs that is believed to have a variety of biological activities, including reducing blood sugar and cholesterol levels, anti-cancer, and anti-diabetes activities. However, little is known about the molecular mechanisms involved. In this study, we showed that protopanaxadiol (PPD), a metabolite of the protopanaxadiol group ginsenosides that are the major pharmacological constituents of ginsengs, significantly altered the expression of genes involved in metabolism, elevated Sestrin2 (Sesn2) expression, activated AMPK, and induced autophagy. Using CRISPR/CAS9-mediated gene editing and shRNA-mediated gene silencing, we demonstrated that Sesn2 is required for PPD-induced AMPK activation and autophagy. Interestingly, we showed that PPD-induced Sesn2 expression is mediated redundantly by the GCN2/ATF4 amino acid-sensing pathway and the PERK/ATF4 endoplasmic reticulum (ER) stress pathway. Our results suggest that ginseng metabolite PPD modulates the metabolism of amino acids and lipids, leading to the activation of the stress-sensing kinases GCN2 and PERK to induce Sesn2 expression, which promotes AMPK activation, autophagy, and metabolic health.