Cyclic AMP stimulates protein synthesis in L6 myoblasts and its effects are additive to those of insulin, vasopressin and 12-0-tetradecanoylphorbol-13-acetate. Possible involvement of mitogen activated protein kinase

Thompson, Michael G.; Mackie, Steven C.; Thom, Amanda; Hazlerigg, David G.; Morrison, Kenneth S.; Palmer, Robert M.

doi:10.1016/0167-4889(95)00194-8

Cited by 11 publications

(6 citation statements)

References 52 publications

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“…We (13) and others (61) reported that insulin stimulates protein synthesis in L6 myoblasts. In addition, insulin enhances the activity of eIF2B in both skeletal muscle (62,63) and CHO cells overexpressing the human insulin receptor (CHO.IR or CHO.T cells) (64).…”

Section: Discussionmentioning

confidence: 99%

Implication of eIF2B Rather Than eIF4E in the Regulation of Global Protein Synthesis by Amino Acids in L6 Myoblasts

Kimball

Horetsky

Jefferson

1998

Journal of Biological Chemistry

151

127

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The present study was designed to investigate the mechanism through which leucine and histidine regulate translation initiation in L6 myoblasts. The results show that both amino acids stimulate initiation and coordinately regulate the activity of eukaryotic initiation factor eIF2B. The changes in eIF2B activity could be explained in part by modulation of the phosphorylation state of the ␣-subunit of eIF2. The activity changes might also be a result of modulation of the phosphorylation state of the eIF2B ⑀-subunit, because deprivation of either amino acid caused a decrease in eIF2B⑀ kinase activity. Leucine, but not histidine, additionally caused a redistribution of eIF4E from the inactive eIF4E⅐4E-BP1 complex to the active eIF4E⅐eIF4G complex. The redistribution was a result of increased phosphorylation of 4E-BP1. The changes in 4E-BP1 phosphorylation and eIF4E redistribution associated with leucine deprivation were not observed in the presence of insulin. However, the leucine-and histidine-induced alterations in global protein synthesis and eIF2B activity were maintained in the presence of the hormone. Overall, the results suggest that both leucine and histidine regulate global protein synthesis through modulation of eIF2B activity. Furthermore, under the conditions employed herein, alterations in eIF4E availability are not ratecontrolling for global protein synthesis but might be necessary for regulation of translation of specific mRNAs.Amino acids play important and multiple roles in regulating protein synthesis in skeletal muscle (1). An obvious role is to act as precursors for protein synthesis. A less obvious but equally important role involves the regulation of translation initiation. The initiation of mRNA translation is a complicated process involving over a dozen proteins, referred to as eukaryotic initiation factors (eIFs) 1 (reviewed in Refs. 2 and 3). Of all the steps in the initiation pathway, only two have been identified that are subject to regulation in vivo; the binding of tRNA iMet to the 40 S ribosomal subunit and the binding of mRNA to the 43 S preinitiation complex. In the first step in initiation, tRNA i Met binds to the 40 S ribosomal subunit as a ternary complex with eIF2 and GTP. Subsequently, the GTP bound to eIF2 is hydrolyzed to GDP, and eIF2 is released from the ribosomal subunit as a complex with GDP. Formation of the ternary complex is regulated by modulation of the activity of a second initiation factor, eIF2B, which mediates guanine nucleotide exchange on eIF2. It is regulated by phosphorylation of the ␣-subunit of eIF2, where phosphorylation converts eIF2 from a substrate into a competitive inhibitor of eIF2B.The binding of mRNA to the 43 S preinitiation complex involves a group of proteins collectively referred to as eIF4 (reviewed in Refs. 2 and 4). The protein that binds to the m 7 GTP cap present at the 5Ј-end of most eukaryotic mRNAs is termed eIF4E. The eIF4E⅐mRNA complex binds to the 40 S ribosomal subunit through the association of eIF4E with eIF4G. An important mechani...

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Section: Discussionmentioning

confidence: 99%

Implication of eIF2B Rather Than eIF4E in the Regulation of Global Protein Synthesis by Amino Acids in L6 Myoblasts

Kimball

Horetsky

Jefferson

1998

Journal of Biological Chemistry

151

127

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“…5 Furthermore, we have previously shown that vasopressin stimulates mitogen-activated protein kinase in these cells (64) and mitogenactivated protein kinase is known to phosphorylate and activate cytosolic PLA 2 (65), releasing arachidonic acid. Thus, it is possible that vasopressin may, at least in part, stimulate protein synthesis in L6 cells through PKC-via mitogen-activated protein kinase, cytosolic PLA 2 , and arachidonic acid.…”

Section: Stimulation Of Protein Synthesis By Exogenous Pld-mentioning

confidence: 99%

Regulation of Phospholipase D in L6 Skeletal Muscle Myoblasts

Thompson¹,

Mackie²,

Thom³

et al. 1997

Journal of Biological Chemistry

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The addition of vasopressin or 12-O-tetradecanoylphorbol-13-acetate (TPA) to prelabeled L6 myoblasts elicited increases in [ 14 C]ethanolamine release, suggesting the activation of phospholipase D activity or activities. While the effects of both agonists on intracellular release were rapid and transient, when extracellular release of [ 14 C]ethanolamine was measured, the effect of vasopressin was again rapid and transient, whereas that of TPA was delayed but sustained. Effects of both agonists on intra-and extracellular release were inhibited by the protein kinase C (PKC) inhibitor, Ro-31-8220, and PKC down-regulation by preincubation with TPA. The formation of phosphatidylbutanol elicited by vasopressin and TPA mirrored their effects on extracellular [ 14 C]ethanolamine release in that the former was transient, whereas the latter was sustained. Responses to both agonists were abolished by PKC down-regulation. When protein synthesis was examined, the stimulation of translation by TPA and transcription by vasopressin were inhibited by Ro-31-8220. In contrast, down-regulation of PKC inhibited the synthesis response to TPA but not vasopressin. Furthermore, following down-regulation, the effect of vasopressin was still blocked by the PKC inhibitors, Ro-31-8220 and bisindolylmaleimide. Analysis of PKC isoforms in L6 cells showed the presence of ␣, ⑀, ␦, , , and . Down-regulation removed both cytosolic (␣) and membrane-bound (⑀ and ␦) isoforms. Thus, the elevation of phospholipase D activity or activities induced by both TPA and vasopressin and the stimulation of translation by TPA involves PKC-␣, -⑀, and/or -␦. In contrast, the increase in transcription elicited by vasopressin involves , , and/or . Hence, although phospholipase D may be linked to increases in translation elicited by TPA, it is not involved in the stimulation of transcription by vasopressin.Loss of skeletal muscle is an acute metabolic response to infection and neoplastic disease and results from a decrease in the rate of protein synthesis and an increase in the rate of protein degradation (e.g. see Refs. 1-3). To reverse this process, an understanding of the signaling pathways regulating protein turnover is essential.We have used 12-O-tetradecanoylphorbol-13-acetate (TPA) 1 and vasopressin to investigate the coordinate regulation of protein turnover. Previous studies in this (4 -6) and other (7) laboratories have shown that these two agents both stimulate protein synthesis and reduce the release of N -methylhistidine, a marker of myofibrillar protein degradation from intact skeletal muscle in vitro and skeletal muscle cells in culture. However, the mechanism(s) mediating these effects are poorly understood.Many extracellular signals such as hormones, neurotransmitters, and growth factors elicit their response by activating an intracellular signaling cascade that is initiated by the hydrolysis of membrane phospholipids (8 -11). In L6 skeletal muscle cells, we have demonstrated that TPA and vasopressin stimulate both protein synthesis and a phospholip...

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“…Oral administration of selected β‐adrenergic agonists (β‐AA) to rodents and livestock increases skeletal muscle mass and diminishes body fat depots (1–5). Likewise, β‐AA increase protein accumulation in cultured myotubes (6, 7) and depress fat accumulation in adipose cells in culture (8). These β‐AA effects can be reversed with the β‐antagonist propranolol (6, 8).…”

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confidence: 99%

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confidence: 99%

“…Ractopamine [a β‐AA] and the cAMP analog dibutyryl‐cAMP increase protein synthesis in L 6 myoblasts (7). Both dibutyrlyl‐cAMP and forskolin appeared to increase mitogen‐activated protein kinase (MAPK) activity in L 6 myoblasts (7). The MAPkinases are critical components in cell surface receptors‐ ras signal transduction pathways that are involved in transcriptional regulation of cell growth and development (16, 17).…”

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confidence: 99%

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β‐Adrenergic Agonist Hyperplastic Effect Is Associated with Increased Fibronectin Gene Expression and Not Mitogen‐Activated Protein Kinase Modulation in C₂C₁₂ Cells

Izevbigie

Bergen

2000

Proc Soc Exp Biol Med

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Abstract. β‐Adrenergic agonists (β‐AA) enhance protein accretion in skeletal muscles. This stimulation is characterized by increased protein synthesis, increased expression of myofibrillar protein genes and a depression in protein degradation in animals, and increased proliferation and DNA synthesis in muscle cells in vitro. The mechanism or signal path in muscle whereby β‐AA would elicit these physiological effects upon binding to the G protein–coupled β‐adrenergic receptor (β‐AR) is unclear. C2C12 myoblasts were used to determine β‐AR ligand binding characteristics, cyclic AMP synthesis in response to isoproterenol (ISO) stimulation, and effects of ISO on DNA synthesis, mitogen activated protein kinase (MAPK), and fibronectin (FN) gene expression. Results showed that C2C12 cells possess β‐AR which are specific, saturable, and of high affinity (Kd = 0.2 nM). Forskolin and ISO stimulated cAMP production by ≈ 20‐fold (P < 0.001) and 17‐fold (P < 0.001), respectively. ISO and the cAMP analog, 8‐bromo‐cAMP (8‐BC) stimulated DNA synthesis in proliferating cells by 150% (P < 0.05) and 200% (P < 0.01), respectively, without modulating MAPK activity, whereas addition of fetal bovine serum to culture resulted in a 500% increase (P < 0.01) in DNA synthesis and MAPK activation. DNA synthesis in C2C12 cells treated with ISO, 8‐BC, or FBS was abolished in the presence of 25 μM PD098059, an MAPK‐kinase inhibitor, suggesting that an MAPK‐dependent pathway is likely involved in C2C12 proliferation. During cAMP elevating agent stimulation, basal MAPK activity may be sufficient, in the presence of other putative signaling molecules, to support proliferation in these cells. ISO or 8‐BC treatment increased FN mRNA by three‐ and seven‐fold, respectively, in growing C2C12 cells implying a connection between increased DNA synthesis and FN gene expression.

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Cyclic AMP stimulates protein synthesis in L6 myoblasts and its effects are additive to those of insulin, vasopressin and 12-0-tetradecanoylphorbol-13-acetate. Possible involvement of mitogen activated protein kinase

Cited by 11 publications

References 52 publications

Implication of eIF2B Rather Than eIF4E in the Regulation of Global Protein Synthesis by Amino Acids in L6 Myoblasts

Implication of eIF2B Rather Than eIF4E in the Regulation of Global Protein Synthesis by Amino Acids in L6 Myoblasts

Regulation of Phospholipase D in L6 Skeletal Muscle Myoblasts

β‐Adrenergic Agonist Hyperplastic Effect Is Associated with Increased Fibronectin Gene Expression and Not Mitogen‐Activated Protein Kinase Modulation in C₂C₁₂ Cells

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Cyclic AMP stimulates protein synthesis in L6 myoblasts and its effects are additive to those of insulin, vasopressin and 12-0-tetradecanoylphorbol-13-acetate. Possible involvement of mitogen activated protein kinase

Cited by 11 publications

References 52 publications

Implication of eIF2B Rather Than eIF4E in the Regulation of Global Protein Synthesis by Amino Acids in L6 Myoblasts

Implication of eIF2B Rather Than eIF4E in the Regulation of Global Protein Synthesis by Amino Acids in L6 Myoblasts

Regulation of Phospholipase D in L6 Skeletal Muscle Myoblasts

β‐Adrenergic Agonist Hyperplastic Effect Is Associated with Increased Fibronectin Gene Expression and Not Mitogen‐Activated Protein Kinase Modulation in C2C12 Cells

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β‐Adrenergic Agonist Hyperplastic Effect Is Associated with Increased Fibronectin Gene Expression and Not Mitogen‐Activated Protein Kinase Modulation in C₂C₁₂ Cells