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 a-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 mM). At a concentration of 4 nM, PIF induced a transient decrease in IkBa levels after 30 min incubation, while no effect was seen at 20 nM PIF. The level of IkBa, an NF-kB inhibitory protein, returned to normal after 60 min. Depletion of IkBa from the cytosol was not seen in myotubes pretreated with EPA, suggesting that the NF-kB/IkB complex was stabilised. At concentrations between 2 and 8 nM, PIF stimulated an increased nuclear migration of NF-kB, which was not seen in myotubes pretreated with EPA. The PIF-induced increase in chymotrypsin-like enzyme activity was also attenuated by the NF-kB inhibitor peptide SN50, suggesting that NF-kB 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-kB accumulation in the nucleus.

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The current study suggests self-efficacy enhancement should be a key component of psycho-behavioral programs designed to support patients with cancer throughout chemotherapy.

The potential role of 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE) as an intracellular signal for increased protein catabolism and induction of the expression of key components of the ubiquitin -proteasome proteolytic pathway induced by a tumour cachectic factor, proteolysis-inducing factor has been studied in murine C 2 C 12 myotubes. 15(S)-HETE induced protein degradation in these cells with a maximal effect at concentrations between 78 and 312 nM. The effect was attenuated by the polyunsaturated fatty acid, eicosapentaenoic acid (EPA). There was an increase in 'chymotrypsin-like' enzyme activity, the predominant proteolytic activity of the proteasome, in the same concentration range as that inducing total protein degradation, and this effect was also attenuated by EPA. 15(S)-hydroxyeicosatetraenoic acid also increased maximal expression of mRNA for proteasome subunits C2 and C5, as well as the ubiquitin-conjugating enzyme, E2 14k , after 4 h incubation, as determined by quantitative competitive RT -PCR. The concentrations of 15-HETE affecting gene expression were the same as those inducing protein degradation. Western blotting of cellular supernatants of myotubes treated with 15(S)-HETE for 24 h showed increased expression of p42, an ATPase subunit of the regulatory complex at similar concentrations, as well as a decrease in expression of myosin in the same concentration range. 15(S)-hydroxyeicosatetraenoic acid activated binding of nuclear factor-kB (NF-kB) in the myotube nucleus and stimulated degradation of I-kBa. The effect on the NF-kB/I-kBa system was attenuated by EPA. In addition, the NF-kB inhibitor peptide SN50 attenuated the increased chymotrypsinlike enzyme activity in the presence of 15(S)-HETE. These results suggest that 15(S)-HETE induces degradation of myofibrillar proteins in differentiated myotubes through an induction of an increased expression of the regulatory components of the ubiquitinproteasome proteolytic pathway possibly through the intervention of the nuclear transcription factor NF-kB, and that this process is inhibited by EPA.

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