Breakdown of aberrant protein in rabbit reticulocytes decreases with cell age.
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ABSTRACT:
SUBMITTER: McKay MJ
PROVIDER: S-EPMC1162566 | biostudies-other | 1980 Apr
REPOSITORIES: biostudies-other
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Project description:An extract was prepared from rabbit reticulocyte ribosomes after treatment with potassium chloride as described by Miller, Hamada, Yang, Cohen & Schweet (1967). This extract has been shown to convert monoribosomes into polyribosomes during protein synthesis in vitro (Cohen, 1968). The nature of this extract was studied in greater detail. Centrifugation of the extract through a sucrose density gradient separated the activity into a fast-sedimenting fraction. The two fractions were shown to have different functions in stimulating cell-free protein synthesis and their active components were shown to be protein or partly protein in nature. Each fraction was analysed by electrophoresis and in the analytical ultracentrifuge. It was concluded that the active component in the fast-sedimenting fraction had a sedimentation coefficient of 15.5s and that of the slow-sedimenting fraction 10.5s.
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Project description:Turnover of mRNA is a critical step that allows cells to control gene expression. Endoribonucleases, enzymes cleaving RNA molecules internally, are some of the key components of the degradation process. Here we provide a detailed characterization of novel endoribonuclease SLFN14 purified from rabbit reticulocyte lysate. Schlafen genes encode a family of proteins limited to mammals. Their cellular function is unknown or incompletely understood. In reticulocytes, SLFN14 is strongly overexpressed, represented exclusively by the short form, all tethered to ribosomes, and appears to be one of the major ribosome-associated proteins. SLFN14 binds to ribosomes and ribosomal subunits in the low part of the body and cleaves RNA but preferentially rRNA and ribosome-associated mRNA. This results in the degradation of ribosomal subunits. This process is strictly Mg(2+)- and Mn(2+)-dependent, NTP-independent, and sequence nonspecific. However, in other cell types, SLFN14 is a full-length solely nuclear protein, which lacks ribosomal binding and nuclease activities. Mutational analysis revealed the ribosomal binding site and the aspartate essential for the endonucleolytic activity of protein. Only few endoribonucleases participating in ribosome-mediated processes have been characterized to date. Moreover, none of them are shown to be directly associated with the ribosome. Therefore, our findings expand the general knowledge of endoribonucleases involved in mammalian translation control.
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Project description:1. The effect of high-molecular-weight RNA from reticulocyte polyribosomes (messenger RNA) on protein synthesis by subcellular fractions derived from reticulocytes, reported by Arnstein, Cox & Hunt (1964), has now been studied in detail. Optimum response of the cell-free system requires 30-50mm-K(+) and approx. 5mm-Mg(2+) in the pH range 7.4-7.6. 2. RNA stimulates the incorporation into protein of both free amino acids and of aminoacyl residues from s-RNA. Stimulation by either RNA or polyuridylic acid is dependent on a labile factor or enzyme, which is present in the ;pH5 fraction' and may be concerned with the formation of new polysomes. Quantitatively the response of the cell-free system to RNA is similar to that of polyuridylic acid, and there appears to be competition between messenger RNA and polyuridylic acid or polyadenylic acid.
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Project description:When radioiron-labelled transferrin with 55Fe located predominantly in the N-terminal iron-binding site and 59Fe predominantly in the C-terminal iron-binding site was incubated with rabbit reticulocytes, both radioisotopes of iron were removed at similar rates. Electrophoresis of transferrin samples taken during the course of an incubation, in polyacrylamide gels containing 6 M-urea, showed that iron was removed in a pairwise fashion, giving rise to iron-free transferrin.
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Project description:1. The incorporation of labelled valine by rabbit reticulocytes into the N-terminal position of nascent haemoglobin was investigated by deaminating the nascent peptides with nitrous acid and isolating labelled alpha-hydroxyisovaleric acid and valine after acid hydrolysis. 2. The amount of radioactivity in alpha-hydroxyisovaleric acid relative to that in valine indicated the presence of 12.3% N-terminal valine having a free amino group. This high value suggests that most if not all nascent peptides contain valine in the N-terminal position. 3. Cell-free preparations containing reticulocyte ribosomes and pH5 enzymes incorporated alpha-hydroxy-[(14)C]isovaleryl-tRNA (where tRNA refers to transfer RNA), which was obtained by deamination of [(14)C]valyl-tRNA from yeast or liver with nitrous acid, into both soluble and nascent protein. 4. When the soluble protein was chromatographed on CM-cellulose, radioactivity was found to be associated with both the alpha-and beta-globin chains. 5. The kinetics of hydrolysis of [(14)C]valine, was also investigated. Most of the material was hydrolysed rapidly at pH10, but a minor component that was relatively stable appeared to be present to the extent of about 10% of the total valyl-tRNA. Valine was, however, the only hydrolysis product detected by paper chromatography. 6. It is concluded that chain initiation in haemoglobin synthesis involves valine as the N-terminal amino acid and that the amino group of nascent protein is probably not substituted.
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Project description:1. Cell-free solutions prepared from rabbit reticulocytes were not able to release iron from rabbit transferrin. 2. The results, which differ from those obtained with Rana catesbeiana immature erythrocytes, indicate that cellular integrity is a requirement for this process in the rabbit reticulocyte system.
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Project description:GNAI2 (G protein subunit alpha i2) is a signaling modulator or transducer, involved in several transmembrane signaling systems, that plays a vital role in the melanogenesis signaling pathway. However, whether GNAI2 regulates cell proliferation and apoptosis in rabbit melanocytes is not known. We found that GNAI2 was differentially expressed in rabbits with different coat colors using qRT-PCR and Wes assays. Furthermore, it was observed that the rabbits with black skin had the highest GNAI2 levels, and those with white skin had the lowest expression. The coding sequence of GNAI2 was successfully cloned and inserted into pcDNA3.1 and pcDNA3.1-Myc vectors. It was observed that the GNAI2 protein was mainly localized in the cytoplasm using the indirect immunofluorescence staining assay. Overexpression of GNAI2 significantly increased melanin content, promoted melanocyte proliferation, and inhibited melanocyte apoptosis. On the contrary, the knockdown of GNAI2 using siRNA had the opposite effect. In addition, GNAI2 significantly increased the mRNA expression levels of the melanin-related genes TYR, GPNMB, PMEL, and DCT in rabbit melanocytes. The results suggested that GNAI2 regulated melanocyte development by promoting melanocyte proliferation and inhibiting apoptosis.
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Project description:Under stress conditions mammalian cells activate compensatory mechanisms to survive and maintain cellular function. During catabolic conditions, such as low nutrients, systemic inflammation, cancer or infections, protein breakdown is enhanced and aminoacids are released from muscles to sustain liver gluconeogenesis and tissues protein synthesis. Proteolysis in muscle is orchestrated by a set of genes named atrophy-related genes. A system that is activated both in short and prolonged stress conditions is the family of Forkhead Box (Fox) O transcription factors. Here, we report that muscle-specific deletion of FoxO members resulted in protection from muscle loss because FoxO family is required for induction of autophagy-lysosome and ubiquitin-proteasome systems. Importantly, FoxOs are required for Akt activity but not for mTOR signalling underlining the concept that FoxOs are upstream mTOR for the control of protein breakdown when nutrients are lacking. Moreover, FoxO family controls the induction of critical genes belonging to several fundamental stress response pathways such as unfolded protein response, ROS detoxification and translational regulation. Finally, we identify a set of novel FoxO-dependent ubiquitin ligases including the recent discovered MUSA11 and a new one, which we named Specific of Muscle Atrophy and Regulated by Transcription (SMART). Our findings identify the critical role of FoxO in regulating a variety of genes belonging to pathways important for stress-response under catabolic conditions. Gene expression in muscles of muscle-specific FoxO 1,3,4 knock-out mice that were fed normally or starved We generated knocked-out FoxO 1,3,4 specifically in muscle by crossing FoxO1-3-4-floxed mice (FoxO1,3,4 f/f) with a transgenic line expressing Cre recombinase under the control of MLC1f promoter to generate muscle-specific FoxO1,3,4 triple knockout mice. These mice were either fed ad libitum or starved. Subsequently gene expression of the gastrocnemius muscles was analyzed. For each of the 4 conditions (FOXO1,3,4 f/f fed or starved, FOXO1,3,4-/- fed or starved), we isolated the gastrocnemius muscles of 3 mice thus yielding 6 muscles per condition. RNA was prepared from these muscles using the TRIzol method (Life Technologies) followed by cleanup with the RNeasy kit (QIAGEN). RNA concentration was determined by spectrophotometry and quality of the RNA was monitored using the Agilent 2100 Bioanalyzer (Agilent Technologies). RNA of the 6 muscles per condition was pooled equimolarly and used for further microarray analysis. cRNA was prepared, labelled and hybridised to Affymetrix Mouse Genome 430 2.0 Arrays using Affymetrix-supplied kits and according to standard Affymetrix protocols. Expression values were summarized using the Mas 5.0 algorithm. Genes that were up- or downregulated upon starvation compared to the fed condition were determined using Excel software. A threshold of 1.5 was used for the fold up-or downregulation consistent with the fold change that can be reliably detected with these type of arrays.
2015-04-24 | E-GEOD-52667 | biostudies-arrayexpress
Project description:Under stress conditions mammalian cells activate compensatory mechanisms to survive and maintain cellular function. During catabolic conditions, such as low nutrients, systemic inflammation, cancer or infections, protein breakdown is enhanced and aminoacids are released from muscles to sustain liver gluconeogenesis and tissues protein synthesis. Proteolysis in muscle is orchestrated by a set of genes named atrophy-related genes. A system that is activated both in short and prolonged stress conditions is the family of Forkhead Box (Fox) O transcription factors. Here, we report that muscle-specific deletion of FoxO members resulted in protection from muscle loss because FoxO family is required for induction of autophagy-lysosome and ubiquitin-proteasome systems. Importantly, FoxOs are required for Akt activity but not for mTOR signalling underlining the concept that FoxOs are upstream mTOR for the control of protein breakdown when nutrients are lacking. Moreover, FoxO family controls the induction of critical genes belonging to several fundamental stress response pathways such as unfolded protein response, ROS detoxification and translational regulation. Finally, we identify a set of novel FoxO-dependent ubiquitin ligases including the recent discovered MUSA11 and a new one, which we named Specific of Muscle Atrophy and Regulated by Transcription (SMART). Our findings identify the critical role of FoxO in regulating a variety of genes belonging to pathways important for stress-response under catabolic conditions. Gene expression in muscles of muscle-specific FoxO 1,3,4 knock-out mice that were fed normally or starved
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