Tris-Acetate Polyacrylamide Gradient Gels for the Simultaneous Electrophoretic Analysis of Proteins of Very High and Low Molecular Mass.

Polyacrylamide gel electrophoresis (PAGE) is one of the most powerful tools used for protein analysis. We describe the use of Tris-acetate buffer and 3-15% polyacrylamide gradient gels to simultaneously separate proteins in the mass range of 10-500 kDa. We show that this system is highly sensitive, it has good resolution and high reproducibility, and it can be used for general applications of PAGE such as Coomassie Brilliant Blue staining and immunoblotting. Moreover, we describe how to generate mini Tris-acetate polyacrylamide gels to use them in miniprotein electrophoresis systems. These economical gels are easy to generate and to manipulate and allow a rapid analysis of proteins. All these features make the Tris-acetate-PAGE system a very helpful tool for protein analysis.

Akt-dependent activation of the heart 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFKFB2) isoenzyme by amino acids.

Reciprocal regulation of metabolism and signaling allows cells to modulate their activity in accordance with their metabolic resources. Thus, amino acids could activate signal transduction pathways that control cell metabolism. To test this hypothesis, we analyzed the effect of amino acids on fructose-2,6-bisphosphate (Fru-2,6-P2) metabolism. We demonstrate that amino acids increase Fru-2,6-P2 concentration in HeLa and in MCF7 human cells. In conjunction with this, 6-phosphofructo-2-kinase activity, glucose uptake, and lactate concentration were increased. These data correlate with the specific phosphorylation of heart 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase (PFKFB2) isoenzyme at Ser-483. This activation was mediated by the PI3K and p38 signaling pathways. Furthermore, Akt inactivation blocked PFKFB2 phosphorylation and Fru-2,6-P2 production, thereby suggesting that the above signaling pathways converge at Akt kinase. In accordance with these results, kinase assays showed that amino acid-activated Akt phosphorylated PFKFB2 at Ser-483 and that knockdown experiments confirmed that the increase in Fru-2,6-P2 concentration induced by amino acids was due to PFKFB2. In addition, similar effects on Fru-2,6-P2 metabolism were observed in freshly isolated rat cardiomyocytes treated with amino acids, which indicates that these effects are not restricted to human cancer cells. In these cardiomyocytes, the glucose consumption and the production of lactate and ATP suggest an increase of glycolytic flux. Taken together, these results demonstrate that amino acids stimulate Fru-2,6-P2 synthesis by Akt-dependent PFKFB2 phosphorylation and activation and show how signaling and metabolism are inextricably linked.

Tris-acetate polyacrylamide gradient gels for the simultaneous electrophoretic analysis of proteins of very high and low molecular mass.

Polyacrylamide gel electrophoresis (PAGE) is one of the most powerful tools used for protein analysis. We describe the use of Tris-acetate buffer and 3-15% polyacrylamide gradient gels to simultaneously separate proteins in the mass range of 10-500 kDa. We show that this system is highly sensitive, it has good resolution and high reproducibility, and that it can be used for general applications of PAGE such as Coomassie Brilliant Blue staining and immunoblotting. Moreover, we describe how to generate mini Tris-acetate polyacrylamide gels to use them in miniprotein electrophoresis systems. These economical gels are easy to generate and to manipulate and allow a rapid analysis of proteins. All these features make the Tris-acetate-PAGE system a very helpful tool for protein analysis.

Amino acids activate mammalian target of rapamycin complex 2 (mTORC2) via PI3K/Akt signaling.

The activity of mammalian target of rapamycin (mTOR) complexes regulates essential cellular processes, such as growth, proliferation, or survival. Nutrients such as amino acids are important regulators of mTOR complex 1 (mTORC1) activation, thus affecting cell growth, protein synthesis, and autophagy. Here, we show that amino acids may also activate mTOR complex 2 (mTORC2). This activation is mediated by the activity of class I PI3K and of Akt. Amino acids induced a rapid phosphorylation of Akt at Thr-308 and Ser-473. Whereas both phosphorylations were dependent on the presence of mTOR, only Akt phosphorylation at Ser-473 was dependent on the presence of rictor, a specific component of mTORC2. Kinase assays confirmed mTORC2 activation by amino acids. This signaling was functional, as demonstrated by the phosphorylation of Akt substrate FOXO3a. Interestingly, using different starvation conditions, amino acids can selectively activate mTORC1 or mTORC2. These findings identify a new signaling pathway used by amino acids underscoring the crucial importance of these nutrients in cell metabolism and offering new mechanistic insights.

Simultaneous electrophoretic analysis of proteins of very high and low molecular mass using Tris-acetate polyacrylamide gels.

To separate and analyze giant and small proteins in the same electrophoresis gel, we have used a 3-15% polyacrylamide gradient gel containing 2.6% of the crosslinker bisacrylamide and 0.2 M of Tris-acetate buffer (pH 7.0). Samples were prepared in a sample buffer containing lithium dodecyl sulphate and were run in the gel described above using Tris-Tricine-SDS-sodium bisulfite buffer, pH 8.2, as electrophoresis buffer. Here, we show that this system can be successfully used for general applications of SDS-PAGE such as CBB staining and immunoblot. Thus, by using Tris-acetate 3-15% polyacrylamide gels, it is possible to simultaneously analyze proteins, in the mass range of 10-500 kDa, such as HERC1 (532 kDa), HERC2 (528 kDa), mTOR (289 kDa), Clathrin heavy chain (192 kDa), RSK (90 kDa), S6K (70 kDa), beta-actin (42 kDa), Ran (24 kDa) and LC3 (18 kDa). This system is highly sensitive since it allows detection from as low as 10 microg of total protein per lane. Moreover, it has a good resolution, low cost, high reproducibility and allows for analysis of proteins in a wide range of weights within a short period of time. All these features together with the use of a standard electrophoresis apparatus make the Tris-acetate-PAGE system a very helpful tool for protein analysis.

ERK and p38 pathways regulate amino acid signalling.

The ribosomal protein S6 kinase 1 (S6K1) is emerging as a common downstream target of signalling by hormones and nutrients such as insulin and amino acids. Here, we have investigated how amino acids signal through the S6K1 pathway. First, we found that a commercial anti-phospho-Thr389-S6K1 antibody detects an 80-90 kDa protein that is rapidly phosphorylated in response to amino acids. Unexpectedly, this phosphorylation was insensitive to both mTOR and PI-3 kinase inhibitors, and knockdown experiments showed that this protein was not S6K1. Looking for candidate targets of this phosphorylation, we found that amino acids stimulated phosphorylation of RSK and MSK kinases at residues that are homologous to Thr389 in S6K1. In turn, these phosphorylations required the activity of either p38 or ERK MAP kinases, which could compensate for each other. Moreover, we show that these MAP kinases are also needed for the amino acid-induced phosphorylation of S6K1 at Thr421/Ser424, as well as for that of S6K1 substrate, the S6 ribosomal protein. Consistent with these results, concomitant inhibition of p38 and ERK pathways also antagonised the well-known effects of amino acids on the process of autophagy. Altogether, these findings demonstrate a previously unknown role for MAP kinases in amino acid signalling.

The ATPase activity of the DNA transporter TrwB is modulated by protein TrwA: implications for a common assembly mechanism of DNA translocating motors.

Conjugative systems contain an essential integral membrane protein involved in DNA transport called the Type IV coupling protein (T4CP). The T4CP of conjugative plasmid R388 is TrwB, a DNA-dependent ATPase. Biochemical and structural data suggest that TrwB uses energy released from ATP hydrolysis to pump DNA through its central channel by a mechanism similar to that used by F1-ATPase or ring helicases. For DNA transport, TrwB couples the relaxosome (a DNA-protein complex) to the secretion channel. In this work we show that TrwA, a tetrameric oriT DNA-binding protein and a component of the R388 relaxosome, stimulates TrwBDeltaN70 ATPase activity, revealing a specific interaction between the two proteins. This interaction occurs via the TrwA C-terminal domain. A 68-kDa complex between TrwBDeltaN70 and TrwA C-terminal domain was observed by gel filtration chromatography, consistent with a 1:1 stoichiometry. Additionally, electron microscopy revealed the formation of oligomeric TrwB complexes in the presence, but not in the absence, of TrwA protein. TrwBDeltaN70 ATPase activity in the presence of TrwA was further enhanced by DNA. Interestingly, maximal ATPase rates were achieved with TrwA and different types of dsDNA substrates. This is consistent with a role of TrwA in facilitating the interaction between TrwB and DNA. Our findings provide a new insight into the mechanism by which TrwB recruits the relaxosome for DNA transport. The process resembles the mechanism used by other DNA-dependent molecular motors, such as the RuvA/RuvB system, to be targeted to the DNA followed by hexamer assembly.