Amino acid deprivation-induced stress response in the bovine renal epithelial cell line NBL-1: induction of HSP 70 by phenylalanine

Dry Period Heat Stress Impacts Mammary Protein Metabolism in the Subsequent Lactation

Simple Summary

Heat stress during the dry period of dairy cows reduces milk yield in the following lactation. Factors such as altered mammary metabolism could impact yields and alter milk composition, including milk protein. We sought to determine if exposure to dry period heat stress would influence mammary milk protein metabolism during the subsequent lactation. Objectives were to first determine the impact of dry period heat stress on milk protein yields and secondly characterize the amino acid and protein profiles in the mammary tissue, milk, and blood to elucidate potential carry-over impact of dry period heat stress on systems that participate directly in milk protein metabolism (i.e., mTOR). We found that heat stress during the dry period reduces milk yield, protein content, and protein yield in the subsequent lactation. The plasma amino acid profile and mammary amino acid transporters are altered in dry period heat-stressed cows, and mammary mTOR signaling proteins are differentially expressed as well. It appears that dry period heat stress impacts mammary metabolism with consequences on milk yield and protein content. The continuous production of high-quality and -quantity milk is vital as a sustainable source of protein in the face of rising global temperatures.

Abstract

Dry period heat stress impairs subsequent milk production, but its impact on milk protein content and yield is inconsistent. We hypothesize that dairy cow exposure to dry period heat stress will reduce milk protein synthesis in the next lactation, potentially through modified amino acid (AA) transport and compromised mTOR signaling in the mammary gland. Cows were enrolled into heat-stressed (dry-HT, n = 12) or cooled (dry-CL, n = 12) treatments for a 46-day dry period then cooled after calving. Milk yield and composition and dry matter intake were recorded, and milk, blood, and mammary tissue samples were collected at 14, 42, and 84 days in milk (DIM) to determine free AA concentrations, milk protein fractions, and mammary AA transporter and mTOR pathway gene and protein expression. Dry matter intake did not significantly differ between treatments pre- or postpartum. Compared with dry-CL cows, milk yield was decreased (32.3 vs. 37.7 ± 1.6 kg/day) and milk protein yield and content were reduced in dry-HT cows by 0.18 kg/day and 0.1%. Further, dry-HT cows had higher plasma concentrations of glutamic acid, phenylalanine, and taurine. Gene expression of key AA transporters was upregulated at 14 and 42 DIM in dry-HT cows. Despite minor changes in mTOR pathway gene expression, the protein 4E-BP1 was upregulated in dry-HT cows at 42 DIM whereas Akt and p70 S6K1 were downregulated. These results indicate major mammary metabolic adaptations during lactation after prior exposure to dry period heat stress.

Cell Stress Induced Stressome Release Including Damaged Membrane Vesicles and Extracellular HSP90 by Prostate Cancer Cells

Tumor cells exhibit therapeutic stress resistance-associated secretory phenotype involving extracellular vesicles (EVs) such as oncosomes and heat shock proteins (HSPs). Such a secretory phenotype occurs in response to cell stress and cancer therapeutics. HSPs are stress-responsive molecular chaperones promoting proper protein folding, while also being released from cells with EVs as well as a soluble form known as alarmins. We have here investigated the secretory phenotype of castration-resistant prostate cancer (CRPC) cells using proteome analysis. We have also examined the roles of the key co-chaperone CDC37 in the release of EV proteins including CD9 and epithelial-to-mesenchymal transition (EMT), a key event in tumor progression. EVs derived from CRPC cells promoted EMT in normal prostate epithelial cells. Some HSP family members and their potential receptor CD91/LRP1 were enriched at high levels in CRPC cell-derived EVs among over 700 other protein types found by mass spectrometry. The small EVs (30-200 nm in size) were released even in a non-heated condition from the prostate cancer cells, whereas the EMT-coupled release of EVs (200-500 nm) and damaged membrane vesicles with associated HSP90α was increased after heat shock stress (HSS). GAPDH and lactate dehydrogenase, a marker of membrane leakage/damage, were also found in conditioned media upon HSS. During this stress response, the intracellular chaperone CDC37 was transcriptionally induced by heat shock factor 1 (HSF1), which activated the CDC37 core promoter, containing an interspecies conserved heat shock element. In contrast, knockdown of CDC37 decreased EMT-coupled release of CD9-containing vesicles. Triple siRNA targeting CDC37, HSP90α, and HSP90β was required for efficient reduction of this chaperone trio and to reduce tumorigenicity of the CRPC cells in vivo. Taken together, we define "stressome" as cellular stress-induced all secretion products, including EVs (200-500 nm), membrane-damaged vesicles and remnants, and extracellular HSP90 and GAPDH. Our data also indicated that CDC37 is crucial for the release of vesicular proteins and tumor progression in prostate cancer.

A Novel Model of Cancer Drug Resistance: Oncosomal Release of Cytotoxic and Antibody-Based Drugs

Extracellular vesicles (EVs), such as exosomes or oncosomes, often carry oncogenic molecules derived from tumor cells. In addition, accumulating evidence indicates that tumor cells can eject anti-cancer drugs such as chemotherapeutics and targeted drugs within EVs, a novel mechanism of drug resistance. The EV-releasing drug resistance phenotype is often coupled with cellular dedifferentiation and transformation in cells undergoing epithelial-mesenchymal transition (EMT), and the adoption of a cancer stem cell phenotype. The release of EVs is also involved in immunosuppression. Herein, we address different aspects by which EVs modulate the tumor microenvironment to become resistant to anticancer and antibody-based drugs, as well as the concept of the resistance-associated secretory phenotype (RASP).

Regulation of amino acid transport in the renal epithelial cell line NBL-1

The activities of the transport systems A, B° and XAG- are induced by various forms of stress in renal epithelial cells. Amino acid deprivation induces System A and XAG- in a protein-synthesis dependent process. In the case of System XAG- evidence is presented that induction of transport does not involve an increase in the amount of mRNA for the transporter or of the amount of transport protein. Preliminary evidence for the existence of a novel glycoprotein which is induced in parallel to the induction of these transport systems is presented. It is suggested that the induction of amino acid transport proteins and of some of the so-called stress proteins may be triggered by a common molecular mechanism.

Molecular architecture of myelinated peripheral nerves is supported by calorie restriction with aging

Peripheral nerves from aged animals exhibit features of degeneration, including marked fiber loss, morphological irregularities in myelinated axons and notable reduction in the expression of myelin proteins. To investigate how protein homeostatic mechanisms change with age within the peripheral nervous system, we isolated Schwann cells from the sciatic nerves of young and old rats. The responsiveness of cells from aged nerves to stress stimuli is weakened, which in part may account for the observed age-associated alterations in glial and axonal proteins in vivo. Although calorie restriction is known to slow the aging process in the central nervous system, its influence on peripheral nerves has not been investigated in detail. To determine if dietary restriction is beneficial for peripheral nerve health and glial function, we studied sciatic nerves from rats of four distinct ages (8, 18, 29 and 38 months) kept on an ad libitum (AL) or a 40% calorie restricted diet. Age-associated reduction in the expression of the major myelin proteins and widening of the nodes of Ranvier are attenuated by the dietary intervention, which is paralleled with the maintenance of a differentiated Schwann cell phenotype. The improvements in nerve architecture with diet restriction, in part, are underlined by sustained expression of protein chaperones and markers of the autophagy-lysosomal pathway. Together, the in vitro and in vivo results suggest that there might be an age-limit by which dietary intervention needs to be initiated to elicit a beneficial response on peripheral nerve health.

Low-frequency electromagnetic fields induce a stress effect upon higher plants, as evident by the universal stress signal, alanine

15N NMR analysis reveals alanine production in Duckweed plants exposed to low intensity sinusoidally varying magnetic fields (SVMF) at 60 and 100Hz, and fed by 15N-labeled ammonium chloride. Alanine does not accumulate in the absence of SVMF. Addition of vitamin C, a radical scavenger, reduced alanine production by 82%, indicating the roll of free radicals in the process. Alanine accumulation in plants and animals in response to exposure to a variety of stress conditions, including SVMF, is a general phenomenon. It is proposed that alanine is a universal first stress signal expressed by cells.

Changes in BiP (GRP78) levels upon HSV-1 infection are strain dependent

BiP (grp78) is a chaperone protein which can also regulate the unfolded protein response of the cell. Levels of BiP increased in cells infected by the small plaque producing, cell associated, neuroinvasive strains of HSV-1 (SP7, 490) but decreased in cells infected with KOS, a large plaque, attenuated strain. BiP protein synthesis continued early in infection and BiP was sequestered and its degradation was limited during SP7 infection. BiP protein synthesis stopped and the protein was degraded in KOS infected cells. These viral strain dependent differences in BiP concentration may influence other aspects of the viral interaction with the target cell and its host.

The role of system A for neutral amino acid transport in the regulation of cell volume

System A is a secondary active, sodium dependent transport system for neutral amino acids. Strictly coupled with Na,K-ATPase, its activity determines the size of the intracellular amino acid pool, through a complex network of metabolic reaction and exchange fluxes. Many hormones and drugs affect system A activity in specific cell models or tissues. In all the cell models tested thus far the activity of the system is stimulated by amino acid starvation, cell cycle progression, and the incubation under hypertonic conditions. These three conditions produce marked alterations of cell volume. The stimulation of system A activity plays an important role in cell volume restoration, through an expansion of the intracellular amino acid pool. Under normal conditions, system A substrates represent a major fraction of cell compatible osmolytes, organic compounds that exert a protein stabilizing effect. It is, therefore, likely that the activation of system A represents a portion of a more complex response triggered by exposure to stresses of various nature. Since system A transporters have been recently cloned, the molecular bases of these regulatory mechanisms will probably be elucidated in a short time.

Induction of calreticulin expression in response to amino acid deprivation in Chinese hamster ovary cells

The role of calreticulin as a stress-induced molecular chaperone protein of the endoplasmic reticulum is becoming more apparent. We characterize here the induction of calreticulin in response to complete amino acid deprivation in Chinese hamster ovary cells. Amino acid deprivation caused a 4-fold increase in calreticulin protein levels over a period of 4-10 h. In addition to an overall increase in protein levels, the glycosylation of calreticulin was increased. This glycosylation event was blocked by tunicamycin and was not required for the increase in calreticulin protein levels. Immunofluorescence studies localized calreticulin to the ER of CHO cells, and no significant change was observed after amino acid deprivation. Northern-blot analysis showed that calreticulin mRNA levels were increased approx. 10-fold in response to complete amino acid deprivation. The response was sensitive to actinomycin D and alpha-amanitin, implying that regulation is primarily at the level of transcription. These results are similar to the large increases in asparagine synthetase mRNA observed in response to amino acid deprivation, but the amino acid-deprivation-response element identified to be involved in asparagine synthetase induction is absent from the calreticulin promoter.

Induction of the stress protein Grp75 by amino acid deprivation in CHO cells does not involve an increase in Grp75 mRNA levels

The induction of the stress protein Grp75 in response to amino acid deprivation of Chinese Hamster Ovary cells was characterised using a specific monoclonal antibody. A 2-fold increase in the Grp75 protein content occurred over a period of 5-10 h after incubation of the cells in amino acid-free medium. A partial induction was obtained when either all non-essential amino acids or all essential amino acids were omitted from the medium indicating a broad-specificity response. Deletion of the single amino acids tryptophan, histidine or phenylalanine from otherwise complete medium also produced a partial induction of the protein. The increase in the level of Grp75 was completely blocked by cycloheximide, but only partially blocked by the inhibitors of mRNA synthesis actinomycin D and alpha-amanitin. A specific cDNA probe for Grp75 was generated by PCR and used to quantify mRNA levels. No increase in Grp75 mRNA was observed during the induction of the protein indicating that the primary regulation of Grp75 expression was not at the transcriptional level. These results contrast with the large increase in asparagine synthetase mRNA which has been shown to occur during amino acid deprivation, and indicate that cells respond to this form of stress by more than one mechanism.

Identification and partial characterization of a novel membrane glycoprotein induced by amino acid deprivation in renal epithelial cells

We have identified a protein of 110 kDa in the renal epithelial cell line NBL-1. which is induced on incubation of the cells in an amino-acid-free medium. The protein was purified on conA-Sepharose and subjected to N-terminal sequencing. The sequence obtained. VDRINFKT, does not correspond to any protein in the databases. Antipeptide antibodies made to this sequence recognised a single protein of 110 kDa in whole cell membranes and in a conconavalin A protein extract. Using the antibody on Western blots, the protein was induced 2.5-3 fold in 10-15 h and the induction was inhibited by cycloheximide and tunicamycin. The protein was found also in rat liver plasma membranes. A procedure for the partial purification of this protein from rat liver is described, and some internal sequence is reported. The possible relationship of the induction of this novel protein to the induction of amino acid transport in these cells by amino acid deprivation is discussed.