Hela cytosolic protein isolated by poly (A)-sepharose chromatography is glyceraldehyde-3-P-dehydrogenase

The mutual interaction of glycolytic enzymes and RNA in post-transcriptional regulation

About three decades ago, researchers suggested that metabolic enzymes participate in cellular processes that are unrelated to their catalytic activity, and the term "moonlighting functions" was proposed. Recently developed advanced technologies in the field of RNA interactome capture now unveil the unexpected RNA binding activity of many metabolic enzymes, as exemplified here for the enzymes of glycolysis. Although for most of these proteins a precise binding mechanism, binding conditions, and physiological relevance of the binding events still await in-depth clarification, several well explored examples demonstrate that metabolic enzymes hold crucial functions in post-transcriptional regulation of protein synthesis. This widely conserved RNA-binding function of glycolytic enzymes plays major roles in controlling cell activities. The best explored examples are glyceraldehyde 3-phosphate dehydrogenase, enolase, phosphoglycerate kinase, and pyruvate kinase. This review summarizes current knowledge about the RNA-binding activity of the ten core enzymes of glycolysis in plant, yeast, and animal cells, its regulation and physiological relevance. Apparently, a tight bidirectional regulation connects core metabolism and RNA biology, forcing us to rethink long established functional singularities.

The sweet side of RNA regulation: glyceraldehyde-3-phosphate dehydrogenase as a noncanonical RNA-binding protein

The glycolytic protein, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), has a vast array of extraglycolytic cellular functions, including interactions with nucleic acids. GAPDH has been implicated in the translocation of transfer RNA (tRNA), the regulation of cellular messenger RNA (mRNA) stability and translation, as well as the regulation of replication and gene expression of many single-stranded RNA viruses. A growing body of evidence supports GAPDH-RNA interactions serving as part of a larger coordination between intermediary metabolism and RNA biogenesis. Despite the established role of GAPDH in nucleic acid regulation, it is still unclear how and where GAPDH binds to its RNA targets, highlighted by the absence of any conserved RNA-binding sequences. This review will summarize our current understanding of GAPDH-mediated regulation of RNA function. WIREs RNA 2016, 7:53-70. doi: 10.1002/wrna.1315 For further resources related to this article, please visit the WIREs website.

Bovine tryptophanyl-tRNA synthetase and glyceraldehyde-3-phosphate dehydrogenase form a complex

Bovine tryptophanyl-tRNA synthetase is able to form a complex with glyceraldehyde-3-phosphate dehydrogenase. The complex formation (i) does not influence the tryptophan-dependent PPi-ATP exchange reaction and (ii) involves predominantly the N-terminal dispensable domain of the synthetase. Glyceraldehyde-3-phosphate dehydrogenase was shown to be capable of interacting simultaneously with tryptophanyl-tRNA synthetase and with ribosomal RNA to form a ternary complex. It is proposed that compartmentation of some aminoacyl-tRNA synthetases in certain cases might be achieved via 'adapter' molecules which can bind at once to ribonucleic acids and to aminoacyl-tRNA synthetases.

Glyceraldehyde-3-phosphate dehydrogenase is one of the three major RNA-binding proteins of rabbit reticulocytes

One of the 3 major RNA-binding proteins of rabbit reticulocytes, a polypeptide of 36 kDa, is identified as glyceraldehyde-3-phosphate dehydrogenase (GAPD). This fact was deduced from the identity of molecular masses, one-dimensional peptide maps and isoelectric points of the 36 kDa protein and GAPD from rabbit muscle. It is concluded that GAPD can bind rather unspecifically different RNAs and polynucleotides. This means that GAPD, like other RNA-binding proteins, can form loose dynamic complexes with polyribosomes. Association of such a kind may be used for compartmentation of glycolysis near polyribosomes.

c-myc gene is transcribed at high rate in G0-arrested fibroblasts and is post-transcriptionally regulated in response to growth factors

There is increasing evidence that at least some of the cellular homologues to retroviral oncogenes (c-onc or proto-oncogenes) are directly linked to the control of cell growth (for a review see ref. 1). Among these, c-myc, the cellular homologue to the avian myelocytomatosis virus (MC29) oncogene, has been shown to express high levels of mRNA during early G0/G1 phase after mitogenic stimulation of T lymphocytes by concanavalin A or of fibroblasts by platelet-derived growth factor (PDGF) or serum. An attractive model proposed for this regulation is that the c-myc gene is strongly repressed in cells arrested in the G0 phase of the cell cycle by a growth factor-sensitive repressor. We have investigated an alternative model of post-transcriptional regulation. This latter model leads to two testable predictions. First, that c-myc mRNA should be unusually unstable, which we have confirmed. And second, that there would be a high level of constitutive expression, a situation opposite to that implied by the repressor model. Here we report that c-myc gene is indeed transcribed at a high rate in G0-arrested chinese hamster lung fibroblasts, although the level of mature c-myc mRNA is barely detectable. The early and dramatic increase in c-myc mRNA levels when these resting cells are stimulated by growth factors is not accompanied by any appreciable change in the transcription rate of c-myc gene. Taken together these findings support a model of post-transcriptional regulation of c-myc expression at the level of mRNA degradation.

Characterization of the transcription products of glyceraldehyde 3-phosphate-dehydrogenase gene in HeLa cells

We have partially purified the messenger RNA coding for glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12) from HeLa cells and obtained a cDNA clone containing part of its sequence. Using this clone to probe electrophoregrams of RNA transferred to nitrocellulose, we have investigated the characteristics of nuclear and cytoplasmic transcripts in these cells. In the cytoplasm, nature GAPDH mRNA was detected in Northern blots as an intense band, apparently unique, of approximately 1400 nucleotides. The half-life of this mRNA was determined both from the decay kinetics, after a chase with actinomycin D, and from the labeling kinetics during an accumulation experiment. Both kinds of experiments yielded a half-life value of about 8 h, while the accumulation experiment indicated that steady-state GAPDH mRNA amounted to about 1.6% of cytoplasmic poly(A)-rich RNA. Much longer species, likely to be restricted to the nucleus, were also detected in RNA extracted from total cells. At least three discrete species of 1600, 4000, 5800 and 6800 bases were observed above a trailing background extending up to about 8000 bases. This value is commensurate with a functional size of the GAPDH transcription unit in the order of 13000 bases, which we determined by measuring the size of the ultraviolet inactivation target. Until direct evidence can be obtained at the genomic level, the present results provide the first clue to the existence of introns, presumably at least four, in a GAPDH gene from a higher eucaryote.

Extreme instability of myc mRNA in normal and transformed human cells

To address the possibility that the expression of the myc gene might be regulated at a post-transcriptional level, we have investigated the half-life of myc mRNA in various cells. Our survey included normal human embryonic fibroblasts as well as transformed human cells of various origins: cervix carcinoma (HeLa), breast carcinoma (MCF7), Burkitt lymphoma (Daudi), and promyelocytic leukemia (HL60). All these cells revealed an extreme instability of myc mRNA (half-life, approximately equal to 10 min), suggesting that the control of myc mRNA degradation might be a general means (although not necessarily exclusive) of regulating both the level and the timing of myc gene expression. Inhibition of protein synthesis resulted in a dramatic stabilization of myc mRNA in HeLa, MCF7, and HL60 cells, suggesting that the controlling element might itself be, at least in these cells, a protein of rapid turnover. This finding opens the way to studying the mechanism of myc mRNA inactivation in these different cell types. However, protein synthesis inhibition had no effect on myc mRNA instability in other transformed (Daudi) cell lines as well as normal embryonic human fibroblasts. These different types of behavior suggest that the post-transcriptional control of myc gene expression might involve multiple factors that would be differently affected in various cell types.

Age-dependent gene induction in quail oviduct. XV. Alterations of the poly(A)-associated protein pattern and of the poly(A) chain length of mRNA

The effect of ageing on polyadenylate [poly(A)] metabolism of mRNA was studied in two age groups of female quails: mature (250-320 days' old) and senescent animals (3-3.5 years' old). In introductory experiments it was shown that poly(A)-associated proteins can not be recovered from cytosol by affinity chromatography. We isolated the poly(A)-associated proteins from polyribosomal poly(A)-ribonucleoprotein complex [poly(A)-RNP] and radioactively labeled them with dansyl chloride. Three main protein species were identified with molecular masses of 48000 (P48), 35000 (P35) and 24000 (P24). During ageing the percentage portion of P48 in poly(A)-RNP from liver (mitotic tissue) and from oviduct or heart (post-mitotic tissue) is reduced at the expense of P35 and P24. Quantitative analyses revealed that the amount of poly(A)-RNP in the different organs decreases significantly with age if the values are based on DNA. The protein content in poly(A)-RNP was found to be reduced especially in post-mitotic tissue. From this finding we assume that the number of poly(A)-associated protein molecules per poly(A) stretch drops from approximately 4.7 molecules (mature oviduct) to 1.9 molecules (senescent oviduct). Control experiments revealed that free, non-polyribosomal poly(A)-RNP accounts only for 10% of total poly(A)-RNP. The size of the poly(A) segment of mRNA decreases with age. After labeling with [3H] dimethylsulfate, the poly(A) stretch from mature oviduct was found to consist mainly of 120-180 AMP units, and those from mature liver and mature heart of 110 and 100, respectively. In organs from senescent animals the percentage of shorter poly(A) stretches is enlarged; on the average, poly(A)-70 chains were detected. These results support the assumption that age-dependent changes occur also on the post-transcriptional level during the maturation steps of poly(A)(-) hnRNA to poly(A)-(+) mRNA.

Cytosolic malic dehydrogenase activity is associated with a putative substrate for the transforming gene product of Rous sarcoma virus

A cellular protein of apparent Mr 34,000--36,000 was suggested as a possible physiological substrate for the protein kinase (EC 2.7.1.37) activity associated with the transforming gene product of Rous sarcoma virus. We find this protein to migrate with an apparent Mr of 38,000 in NaDodSO4/polyacrylamide gels. It was not separable from cytosolic malic dehydrogenase activity when purified by chromatography on DEAE-Sephacel, hydroxylapatite, poly(A)-Sepharose, and blue Sepharose, by gel filtration, and by isoelectric focusing. The Mr 38,000 protein as well as cytosolic malic dehydrogenase activity focused with a pI of 7.5. In gel filtration experiments, both displayed an apparent native Mr of 68,000. The male dehydrogenase activity contained in homogeneous preparations of the Mr 38,000 protein had a specific activity of up to 130 units/mg of protein. The recovery of the enzyme was 5--10% of the activity in the extract. Antiserum against the Mr 38,000 protein inactivated the malic dehydrogenase activity associated with the Mr 38,000 protein.