Increased expression of the ubiquitin-proteasome pathway in murine myotubes by proteolysis-inducing factor (PIF) is associated with activation of the transcription factor NF-kappaB

Br J Cancer. 2003 Sep 15;89(6):1116-22. doi: 10.1038/sj.bjc.6601132.

Abstract

Proteolysis-inducing factor (PIF), isolated from a cachexia-inducing murine tumour, has been shown to stimulate protein breakdown in C(2)C(12) myotubes. The effect was attenuated by the specific proteasome inhibitor lactacystin and there was an elevation of proteasome 'chymotrypsin-like' enzyme activity and expression of 20S proteasome alpha-subunits at concentrations of PIF between 2 and 16 nM. Higher concentrations of PIF had no effect. The action of PIF was attenuated by eicosapentaenoic acid (EPA) (50 microM). At a concentration of 4 nM, PIF induced a transient decrease in IkappaBalpha levels after 30 min incubation, while no effect was seen at 20 nM PIF. The level of IkappaBalpha, an NF-kappaB inhibitory protein, returned to normal after 60 min. Depletion of IkappaBalpha from the cytosol was not seen in myotubes pretreated with EPA, suggesting that the NF-kappaB/IkappaB complex was stabilised. At concentrations between 2 and 8 nM, PIF stimulated an increased nuclear migration of NF-kappaB, which was not seen in myotubes pretreated with EPA. The PIF-induced increase in chymotrypsin-like enzyme activity was also attenuated by the NF-kappaB inhibitor peptide SN50, suggesting that NF-kappaB may be involved in the PIF-induced increase in proteasome expression. The results further suggest that EPA may attenuate protein degradation induced by PIF, at least partly, by preventing NF-kappaB accumulation in the nucleus.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blood Proteins / pharmacology*
  • Blotting, Western
  • Cachexia / metabolism
  • Cells, Cultured / drug effects
  • Cells, Cultured / metabolism
  • Chymotrypsin / metabolism
  • Colonic Neoplasms / genetics
  • Colonic Neoplasms / metabolism
  • Cysteine Endopeptidases / genetics
  • Cysteine Endopeptidases / metabolism*
  • DNA Primers / chemistry
  • DNA Primers / genetics
  • Eicosapentaenoic Acid / pharmacology
  • Electrophoretic Mobility Shift Assay
  • Female
  • Fungal Proteins*
  • Gene Expression Regulation
  • I-kappa B Proteins / metabolism
  • Mice
  • Mice, Knockout
  • Multienzyme Complexes / genetics
  • Multienzyme Complexes / metabolism*
  • Muscle Fibers, Skeletal / drug effects*
  • Muscle Fibers, Skeletal / metabolism
  • NF-KappaB Inhibitor alpha
  • NF-kappa B / antagonists & inhibitors
  • NF-kappa B / genetics
  • NF-kappa B / metabolism*
  • Proteasome Endopeptidase Complex
  • Proteins / metabolism
  • Proteoglycans
  • Transcription Factors / deficiency
  • Transcription Factors / genetics
  • Transcription Factors / metabolism
  • Ubiquitins / metabolism*

Substances

  • Blood Proteins
  • DNA Primers
  • Fungal Proteins
  • I-kappa B Proteins
  • Multienzyme Complexes
  • NF-kappa B
  • Nfkbia protein, mouse
  • Proteins
  • Proteoglycans
  • Transcription Factors
  • Ubiquitins
  • proteolysis-inducing peptide
  • NF-KappaB Inhibitor alpha
  • Eicosapentaenoic Acid
  • Chymotrypsin
  • Cysteine Endopeptidases
  • Proteasome Endopeptidase Complex