Increasing the methionine (Met) supply to lactating cows will increase mammary cell proliferation. Activating transcription factor 4 (ATF4) is a regulator of cellular amino acid sensing, linking nutrient signals to cellular anabolism; however, its role in regulating bovine mammary epithelial cell (BMEC) proliferation remains largely unknown. In this study, ATF4 expression paralleled that of Cyclin D1 in mammary tissues from dairy cows at different developmental stages (puberty, lactation and dry period), suggesting that ATF4 is associated with cell proliferation. In BMECs, knockdown of ATF4 increased the number of cells arrested in the G1 phase (∼11%; P < 0.05; control) and downregulated Cyclin D1 expression (∼40%; P < 0.05; control), indicating that ATF4 is required for cell proliferation. Treatment of BMECs with increasing concentrations of Met (0, 0.3, 0.6, 0.9, 1.0 and 1.2 mM) showed that 0.6 mM Met enhanced mammalian target of rapamycin (mTOR) phosphorylation and increased protein expression of ATF4 and Cyclin D1, without activating canonical endoplasmic reticulum stress markers. Inhibition assays demonstrated that mTOR is required for Met-induced ATF4 activation. Functional studies further revealed that ATF4 is a key mediator of Met-regulated cell proliferation. Mechanistically, Met facilitated the physical interaction between ATF4 and glycogen synthase kinase-3β (GSK3β), promoting GSK3β phosphorylation at Ser9 and subsequently increasing Cyclin D1 expression. Collectively, these findings indicate that Met promotes BMEC proliferation through the mTOR-ATF4-GSK3β signalling pathway, providing a potential nutritional strategy to enhance mammary cell proliferation in dairy cows.

Tryptophan (Trp) is an essential amino acid acting as a key nutrition factor regulating animal growth and development. But how Trp modulates food intake in pigs is still not well known. Here, we investigated the effect of dietary supplementation of Trp with different levels on food intake of growing pigs. The data showed that dietary Trp supplementation with the standardised ileal digestibility (SID) Trp to lysine (Lys) ratio at both 0·18 and 0·20 significantly increased the food intake by activating the expression of orexigenic gene agouti-related peptide (AgRP) and inhibiting the expression of anorexigenic gene pro-opiomelanocortin (POMC), cocaine- and amphetamine-regulated transcript (CART) and melanocortin receptor 4 (MC4R) in the hypothalamus. Meanwhile, the level of anorexigenic hormones appetite-regulating peptide YY (PYY) in the duodenum and serum and leptin receptor in the duodenum were also significantly decreased. Importantly, both the kynurenine and serotonin metabolic pathways were activated upon dietary Trp supplementation to downregulate MC4R expression in the hypothalamus. Further mechanistic studies revealed that the reduced MC4R expression activated the hypothalamic AMP-activated protein kinase (AMPK) pathway, which in turn inhibited the mammalian target of rapamycin (mTOR)/S6 kinase 1 (S6K1) activity to stimulate food intake. Together, our study unravels the orexigenic effect of dietary Trp supplementation in pigs and expands its potential application in developing nutrition intervention strategy in pig production.

Methionine (Met) can activate the mechanistic target of rapamycin (mTOR) to promote milk synthesis in mammary epithelial cells. However, it is largely unknown which G protein-coupled receptor can mediate the stimulation of Met on mTOR activation. In this study, we employed transcriptome sequencing to analyse which G protein-coupled receptors were associated with the role of Met and further used gene function study approaches to explore the role of G protein-coupled receptor 183 (GPR183) in Met stimulation on mTOR activation in HC11 cells. We identified nine G protein-coupled receptors including GPR183 whose expression levels were upregulated by Met treatment through RNA sequencing and subsequent quantitative real-time PCR analysis. Using GPR183 knockdown and overexpression technology, we demonstrate that GPR183 is a positive regulator of milk protein and fat synthesis and proliferation of HC11 cells. Met affected GPR183 expression in a dose-dependent manner, and GPR183 mediated the stimulation of Met (0·6 mM) on milk protein and fat synthesis, cell proliferation and mTOR phosphorylation and mRNA expression. The inhibition of phosphoinositide 3-kinase blocked the phosphorylation of mTOR and AKT stimulated by GPR183 activation. In summary, through RNA sequencing and gene function study, we uncover that GPR183 is a key mediator for Met to activate the phosphoinositide 3-kinase-mTOR signalling and milk synthesis in mouse mammary epithelial cells.

Taurine (Tau) has many profound physiological functions, but its role and molecular mechanism in muscle cells are still not fully understood. In this study, we investigated the role and underlying molecular mechanism of Tau on protein synthesis and proliferation of C2C12 myoblast cells. Cells were treated with Tau (0, 60, 120, 180 and 240 μM) for 24 h. Tau dose-dependently promoted protein synthesis, cell proliferation, mechanistic target of rapamycin protein (mTOR) phosphorylation and also AT-rich interaction domain 4B (ARID4B) expression, with the best stimulatory effects at 120 μM. LY 294002 treatment showed that Tau promoted ARID4B expression in a phosphoinositide 3-kinase (PI3K)-dependent manner. ARID4B knockdown (by small interfering RNA transfection for 24 h) prevented Tau from stimulating protein synthesis and cell proliferation, whereas ARID4B gene activation (using the CRISPR/dCas9 technology) had stimulatory effects. ARID4B knockdown abolished Tau signalling to mRNA expression and protein phosphorylation of mTOR, whereas ARID4B gene activation had stimulatory effects. Chromatin immunoprecipitation (ChIP)-PCR identified that all of ARID4B, H3K27ac and H3K27me3 bound to the −4368 to –4591 bp site in the mTOR promoter, and ChIP-quantitative PCR (qPCR) further detected that Tau stimulated ARID4B binding to this site. ARID4B knockdown or gene activation did not affect H3K27me3 binding to the mTOR promoter but decreased or increased H3K27ac binding, respectively. Furthermore, ARID4B knockdown abolished the stimulation of Tau on H3K27ac binding to the mTOR promoter. In summary, these data uncover that Tau promotes protein synthesis and proliferation of C2C12 myoblast cells through the PI3K-ARID4B-mTOR pathway, providing a deep understanding of how Tau regulates anabolism in muscle cells.

Idiopathic intrauterine growth restriction (IUGR) is a result of impaired placental nutrient supply. Newborns with IUGR exhibiting postnatal catch-up growth are of higher risk for cardiovascular and metabolic co-morbidities in adult life. Mammalian target of rapamycin (mTOR) was recently shown to function as a placental nutrient sensor. Thus, we determined possible correlations of members of the placental mTOR signaling cascade with auxologic parameters of postnatal growth. The protein expression and activity of mTOR-pathway signaling components, Akt, AMP-activated protein kinase α, mTOR, p70S6kinase1 and insulin receptor substrate-1 were analysed via western blotting in IUGR v. matched appropriate-for-gestational age (AGA) placentas. Moreover, mTOR was immunohistochemically stained in placental sections. Data from western blot analyses were correlated with retrospective auxological follow-up data at 1 year of age. We found significant catch-up growth in the 1st year of life in the IUGR group. MTOR and its activated form are immunohistochemically detected in multiple placental compartments. We identified correlations of placental mTOR-pathway signaling components to auxological data at birth and at 1 year of life in IUGR. Analysis of the protein expression and phosphorylation level of mTOR-pathway components in IUGR and AGA placentas postpartum, however, did not reveal pathognomonic changes. Our findings suggest that the level of activated mTOR correlates with early catch-up growth following IUGR. However, the complexity of signals converging at the mTOR nexus and its cellular distribution pattern seem to limit its potential as biomarker in this setting.

The maladaptive drug memory developed between the drug-rewarding effect and environmental cues contributes to difficulty in preventing drug relapse. Established reward memories can be disrupted by pharmacologic interventions following their reactivation. Rapamycin, an inhibitor of mammalian target of rapamycin (mTOR) kinase, has been proved to be involved in various memory consolidation. However, it is less well characterized in drug memory reconsolidation. Using a conditioned place preference (CPP) procedure, we examined the effects of systemically administered rapamycin on reconsolidation of drug memory in rats. We found that systemically administered rapamycin (0.1 or 10 mg/kg, i.p.) after re-exposure to drug-paired environment, dose dependently decreased the expression of CPP 1 d later, and the effect lasted for up to 14 d and could not be reversed by a priming injection of morphine. The effect of rapamycin on morphine-associated memory was specific to drug-paired context, and rapamycin had no effect on subsequent CPP expression when rats were exposed to saline-paired context or homecage. These results indicated that systemic administration of rapamycin after memory reactivation can persistently inhibit the drug seeking behaviour via disruption of morphine memory reconsolidation in rats. Additionally, the effect of rapamycin on memory reconsolidation was reproduced in cocaine CPP and alcohol CPP. Furthermore, rapamycin did not induce conditioned place aversion and had no effect on locomotor activity and anxiety behaviour. These findings suggest that rapamycin could erase the acquired drug CPP in rats, and that mTOR activity plays an important role in drug reconsolidation and is required for drug relapse.

Human tumours emerge as the result of multiple genetic and epigenetic aberrations that allow the proto-cancer cell to escape normal social control. Many signal transduction pathways become constitutively active during this process, and one whose importance is increasingly being appreciated involves phosphoinositide 3-kinase (PI3-kinase). This pathway normally regulates important cell decisions such as growth, division, survival and migration, and when deregulated it can confer malignant potential to the ensuing tumour. However, constitutive activation of the PI3-kinase pathway might provide attractive therapeutic targets for the design of small-molecule inhibitors. This review discusses events upstream and downstream of PI3-kinase activity in the PI3-kinase signalling pathway, how PI3-kinase is deregulated in human tumourigenesis, and how this is being targeted clinically.