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Signal transduction pathways involved in proteolysis-inducing factor induced proteasome expression in murine myotubes.

Smith HJ, Tisdale MJ - Br. J. Cancer (2003)

Bottom Line: This suggests that both PLA(2) and PLC are involved in the release of AA in response to PIF, and that this is important in the induction of proteasome expression.The two tyrosine kinase inhibitors genistein and tryphostin A23 also attenuated PIF-induced proteasome expression, implicating tyrosine kinase in this process.PIF induced phosphorylation of p44/42 mitogen-activated protein kinase (MAPK) at the same concentrations as that inducing proteasome expression, and the effect was blocked by PD98059, an inhibitor of MAPK kinase, as was also the induction of proteasome expression, suggesting a role for MAPK activation in PIF-induced proteasome expression.

View Article: PubMed Central - PubMed

Affiliation: Pharmaceutical Sciences Research Institute, Aston University, Birmingham B4 7ET, UK.

ABSTRACT
The proteolysis-inducing factor (PIF) is produced by cachexia-inducing tumours and initiates protein catabolism in skeletal muscle. The potential signalling pathways linking the release of arachidonic acid (AA) from membrane phospholipids with increased expression of the ubiquitin-proteasome proteolytic pathway by PIF has been studied using C(2)C(12) murine myotubes as a surrogate model of skeletal muscle. The induction of proteasome activity and protein degradation by PIF was blocked by quinacrine, a nonspecific phospholipase A(2) (PLA(2)) inhibitor and trifluroacetyl AA, an inhibitor of cytosolic PLA(2). PIF was shown to increase the expression of calcium-independent cytosolic PLA(2), determined by Western blotting, at the same concentrations as those inducing maximal expression of 20S proteasome alpha-subunits and protein degradation. In addition, both U-73122, which inhibits agonist-induced phospholipase C (PLC) activation and D609, a specific inhibitor of phosphatidylcholine-specific PLC also inhibited PIF-induced proteasome activity. This suggests that both PLA(2) and PLC are involved in the release of AA in response to PIF, and that this is important in the induction of proteasome expression. The two tyrosine kinase inhibitors genistein and tryphostin A23 also attenuated PIF-induced proteasome expression, implicating tyrosine kinase in this process. PIF induced phosphorylation of p44/42 mitogen-activated protein kinase (MAPK) at the same concentrations as that inducing proteasome expression, and the effect was blocked by PD98059, an inhibitor of MAPK kinase, as was also the induction of proteasome expression, suggesting a role for MAPK activation in PIF-induced proteasome expression.

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Western blot of soluble extracts of C2C12 myotubes treated with 0 (lanes 1 and 7); 1.0 (lanes 2 and 8); 2.1 (lanes 3 and 9); 4.2 (lanes 4 and 10); 10 (lanes 5 and 11) or 20 nM PIF (lanes 6 and 12) in the absence (lanes 1–6) or after 2 h pretreatment with trifluoroacetyl AA (20 μM) (lanes 7–12). Bands were detected using either antibody to 20S proteasome α-subunits (A), iPLA2 (B) or β-tubulin (C). The blots shown are representative of at least three separate experiments.
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fig2: Western blot of soluble extracts of C2C12 myotubes treated with 0 (lanes 1 and 7); 1.0 (lanes 2 and 8); 2.1 (lanes 3 and 9); 4.2 (lanes 4 and 10); 10 (lanes 5 and 11) or 20 nM PIF (lanes 6 and 12) in the absence (lanes 1–6) or after 2 h pretreatment with trifluoroacetyl AA (20 μM) (lanes 7–12). Bands were detected using either antibody to 20S proteasome α-subunits (A), iPLA2 (B) or β-tubulin (C). The blots shown are representative of at least three separate experiments.

Mentions: Effect of PIF concentration on the chymotrypsin-like enzyme activity of the proteasome in C2C12 myotubes in the absence (×) and presence (▪) of (A) quinacrine (5 μM) or (B) trifluoroacetyl AA (20 μM). (C) The effect of quinacrine (5 μM) (□), trifluoroacety l AA (20 μM) (▪) and PD98059 (10 μM) (□) on protein degradation determined by the release of phenylalanine as previously described (Gomes-Marcondes et al, 2002) in murine myotubes in the presence of PIF. The experiments were repeated three times (n=9). Differences from control are indicated as a, P<0.01 and b, P<0.001, while differences from those in the absence of the inhibitors are indicated as c, P<0.0001. The inhibitors were added to the cells 2 h prior to PIF.


Signal transduction pathways involved in proteolysis-inducing factor induced proteasome expression in murine myotubes.

Smith HJ, Tisdale MJ - Br. J. Cancer (2003)

Western blot of soluble extracts of C2C12 myotubes treated with 0 (lanes 1 and 7); 1.0 (lanes 2 and 8); 2.1 (lanes 3 and 9); 4.2 (lanes 4 and 10); 10 (lanes 5 and 11) or 20 nM PIF (lanes 6 and 12) in the absence (lanes 1–6) or after 2 h pretreatment with trifluoroacetyl AA (20 μM) (lanes 7–12). Bands were detected using either antibody to 20S proteasome α-subunits (A), iPLA2 (B) or β-tubulin (C). The blots shown are representative of at least three separate experiments.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2394402&req=5

fig2: Western blot of soluble extracts of C2C12 myotubes treated with 0 (lanes 1 and 7); 1.0 (lanes 2 and 8); 2.1 (lanes 3 and 9); 4.2 (lanes 4 and 10); 10 (lanes 5 and 11) or 20 nM PIF (lanes 6 and 12) in the absence (lanes 1–6) or after 2 h pretreatment with trifluoroacetyl AA (20 μM) (lanes 7–12). Bands were detected using either antibody to 20S proteasome α-subunits (A), iPLA2 (B) or β-tubulin (C). The blots shown are representative of at least three separate experiments.
Mentions: Effect of PIF concentration on the chymotrypsin-like enzyme activity of the proteasome in C2C12 myotubes in the absence (×) and presence (▪) of (A) quinacrine (5 μM) or (B) trifluoroacetyl AA (20 μM). (C) The effect of quinacrine (5 μM) (□), trifluoroacety l AA (20 μM) (▪) and PD98059 (10 μM) (□) on protein degradation determined by the release of phenylalanine as previously described (Gomes-Marcondes et al, 2002) in murine myotubes in the presence of PIF. The experiments were repeated three times (n=9). Differences from control are indicated as a, P<0.01 and b, P<0.001, while differences from those in the absence of the inhibitors are indicated as c, P<0.0001. The inhibitors were added to the cells 2 h prior to PIF.

Bottom Line: This suggests that both PLA(2) and PLC are involved in the release of AA in response to PIF, and that this is important in the induction of proteasome expression.The two tyrosine kinase inhibitors genistein and tryphostin A23 also attenuated PIF-induced proteasome expression, implicating tyrosine kinase in this process.PIF induced phosphorylation of p44/42 mitogen-activated protein kinase (MAPK) at the same concentrations as that inducing proteasome expression, and the effect was blocked by PD98059, an inhibitor of MAPK kinase, as was also the induction of proteasome expression, suggesting a role for MAPK activation in PIF-induced proteasome expression.

View Article: PubMed Central - PubMed

Affiliation: Pharmaceutical Sciences Research Institute, Aston University, Birmingham B4 7ET, UK.

ABSTRACT
The proteolysis-inducing factor (PIF) is produced by cachexia-inducing tumours and initiates protein catabolism in skeletal muscle. The potential signalling pathways linking the release of arachidonic acid (AA) from membrane phospholipids with increased expression of the ubiquitin-proteasome proteolytic pathway by PIF has been studied using C(2)C(12) murine myotubes as a surrogate model of skeletal muscle. The induction of proteasome activity and protein degradation by PIF was blocked by quinacrine, a nonspecific phospholipase A(2) (PLA(2)) inhibitor and trifluroacetyl AA, an inhibitor of cytosolic PLA(2). PIF was shown to increase the expression of calcium-independent cytosolic PLA(2), determined by Western blotting, at the same concentrations as those inducing maximal expression of 20S proteasome alpha-subunits and protein degradation. In addition, both U-73122, which inhibits agonist-induced phospholipase C (PLC) activation and D609, a specific inhibitor of phosphatidylcholine-specific PLC also inhibited PIF-induced proteasome activity. This suggests that both PLA(2) and PLC are involved in the release of AA in response to PIF, and that this is important in the induction of proteasome expression. The two tyrosine kinase inhibitors genistein and tryphostin A23 also attenuated PIF-induced proteasome expression, implicating tyrosine kinase in this process. PIF induced phosphorylation of p44/42 mitogen-activated protein kinase (MAPK) at the same concentrations as that inducing proteasome expression, and the effect was blocked by PD98059, an inhibitor of MAPK kinase, as was also the induction of proteasome expression, suggesting a role for MAPK activation in PIF-induced proteasome expression.

Show MeSH
Related in: MedlinePlus