Nutritional Biomedicine, School of Life and Health Sciences, Aston University, Birmingham B4 7ET, UK.
Br J Cancer. 2011 Jun 28;105(1):83-8. doi: 10.1038/bjc.2011.216. Epub 2011 Jun 14.
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.
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 C(2)C(12) murine myotubes, while in vivo studies employed mice bearing the cachexia-inducing MAC16 tumour.
The process resulted in almost a 23,000-fold purification of PIF, but with a recovery of only 0.004%. Both the D- and L-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 L-peptides significantly attenuated weight loss, although the D-peptide did show a tendency to increase lean body mass.
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.
癌症恶病质中骨骼肌萎缩归因于肿瘤产生的高度糖基化肽，称为蛋白水解诱导因子（PIF）。PIF 的作用是通过肌肉中的高亲和力膜受体介导的。本研究调查了源自受体 20 个 N 端氨基酸的肽在体外和体内中和 PIF 作用的能力。
使用初始蛋白酶消化从 MAC16 肿瘤中纯化蛋白水解诱导因子，然后结合在 DEAE 纤维素上，并通过加热至 80°C 使蛋白酶失活，然后使用亲和层析纯化 PIF。体外研究使用 C(2)C(12)鼠肌管进行，而体内研究则使用诱导恶病质的 MAC16 肿瘤的小鼠进行。
该过程导致 PIF 的纯化度几乎提高了 23,000 倍，但回收率仅为 0.004%。20 肽的 D-和 L-形式都通过泛素-蛋白酶体蛋白水解途径减弱了 PIF 诱导的体外蛋白降解，并增加了肌球蛋白的表达。体内研究表明，D-和 L-肽都没有显著减轻体重减轻，尽管 D-肽确实有增加瘦体重的趋势。
这些结果表明，这些肽可能由于亲水性太强而不能用作治疗剂，但证实了受体在 PIF 对肌肉蛋白降解的作用中的重要性。
