Attenuation of muscle atrophy by an N-terminal peptide of the receptor for proteolysis-inducing factor (PIF)

Abstract

Background:Atrophy of skeletal muscle in cancer cachexia has been attributed to a tumour-produced highly glycosylated peptide called proteolysis-inducing factor (PIF). The action of PIF is mediated through a high-affinity membrane receptor in muscle. This study investigates the ability of peptides derived from the 20 N-terminal amino acids of the receptor to neutralise PIF action both in vitro and in vivo.Methods:Proteolysis-inducing factor was purified from the MAC16 tumour using an initial pronase digestion, followed by binding on DEAE cellulose, and the pronase was inactivated by heating to 80°C, before purification of the PIF using affinity chromatography. In vitro studies were carried out using C2C12 murine myotubes, while in vivo studies employed mice bearing the cachexia-inducing MAC16 tumour.Results:The process resulted in almost a 23 000-fold purification of PIF, but with a recovery of only 0.004%. Both the - and -forms of the 20mer peptide attenuated PIF-induced protein degradation in vitro through the ubiquitin-proteosome proteolytic pathway and increased expression of myosin. In vivo studies showed that neither the D- nor the -peptides significantly attenuated weight loss, although the -peptide did show a tendency to increase lean body mass.Conclusion:These results suggest that the peptides may be too hydrophilic to be used as therapeutic agents, but confirm the importance of the receptor in the action of the PIF on muscle protein degradation.

The Multiple Facets of Dermcidin in Cell Survival and Host Defense

“…The glycosylation of PIF is essential for its proteolytic activity as neither the peptide core alone nor the deglycosylated native PIF has any effect on weight loss in mice [19,25]. Further studies provided evidence that PIF is present in the urine of weight-losing cancer patients with a variety of malignancies, including cancer of the pancreas, breast, ovary and lung [12,14,24,28,29,51,52]. However, PIF represents only 5 × 10 –4 % of the total urinary proteins [51].…”

“…Many studies followed, describing the presence of PIF in mouse and human cancer cell lines, such as the human melanoma cell line G361, and in the urine of cachectic cancer patients [25,50,51]. Further studies by this group provided evidence that PIF is present in weight-losing cancer patients with a variety of malignancies, including cancer of the pancreas, breast, ovary and lung [12,14,24,28,29,51,52]. However, neither the expression nor the functional studies could be reproduced by other groups [15,16,19,53,54,55].…”

“…Furthermore, other vertebrates, such as wallabies, cats, dogs, horses or rodents, do not have dermcidin homologous genes [23]. Based on these facts, it is very astonishing that several publications claim that dermcidin is expressed in mice [19,24,25,26,27,28,29,30,31,32], rats [33] and the tammar wallaby [34]. In summary, since dermcidin homologous genes are only found in primates, one can conclude that dermcidin is an orphan gene.…”

“…Mirza et al [29 ]found that an N -terminal peptide of the PIF receptor attenuated muscle atrophy. However, although PIF attenuated protein degradation in vitro, in vivo studies showed that PIF does not significantly attenuate weight loss in mice.…”

The Use of Ghrelin and Ghrelin Receptor Agonists as a Treatment for Animal Models of Disease: Efficacy and Mechanism

“…The implanted cell lines differ from most human cancers in that they do not metastasize significantly but they are similar in many other ways to cachexia-causing neoplasms in humans. This includes stimulation of host-tumor interactions and in some cases release of cachexia-inducing factors [57,58]. Many of these implanted tumor cells express or induce inflammatory cytokines or prostaglandins [59–62].…”