Bera Soumen, Wallimann Theo, Ray Subhankar, Ray Manju
Department of Biological Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata, India.
FEBS J. 2008 Dec;275(23):5899-909. doi: 10.1111/j.1742-4658.2008.06718.x.
The creatine/creatine kinase system decreases drastically in sarcoma. In the present study, an investigation of catalytic activities, western blot and mRNA expression unambiguously demonstrates the prominent expression of the creatine-synthesizing enzymes l-arginine:glycine amidinotransferase and N-guanidinoacetate methyltransferase in sarcoma, Ehrlich ascites carcinoma and Sarcoma 180 cells, whereas both enzymes were virtually undetectable in normal muscle. Compared to that of normal animals, these enzymes remained unaffected in the kidney or liver of sarcoma-bearing mice. High activity and expression of mitochondrial arginase II in sarcoma indicated increased ornithine formation. Slightly or moderately higher levels of ornithine, guanidinoacetate and creatinine were observed in sarcoma compared to muscle. Despite the intrinsically low level of creatine in Ehrlich ascites carcinoma and Sarcoma 180 cells, these cells could significantly take up and release creatine, suggesting a functional creatine transport, as verified by measuring mRNA levels of creatine transporter. Transcript levels of arginase II, ornithine-decarboxylase, S-adenosyl-homocysteine hydrolase and methionine-synthase were significantly upregulated in sarcoma and in Ehrlich ascites carcinoma and Sarcoma 180 cells. Overall, the enzymes related to creatine and arginine/methionine metabolism were found to be significantly upregulated in malignant cells. However, the low levels of creatine kinase in the same malignant cells do not appear to be sufficient for the building up of an effective creatine/phosphocreatine pool. Instead of supporting creatine biosynthesis, l-arginine:glycine amidinotransferase and N-guanidinoacetate methyltransferase appear to be geared to support cancer cell metabolism in the direction of polyamine and methionine synthesis because both these compounds are in high demand in proliferating cancer cells.
肌酸/肌酸激酶系统在肉瘤中急剧减少。在本研究中，对催化活性、蛋白质印迹和mRNA表达的研究明确表明，肌酸合成酶L-精氨酸：甘氨酸脒基转移酶和N-胍基乙酸甲基转移酶在肉瘤、艾氏腹水癌和肉瘤180细胞中显著表达，而在正常肌肉中几乎检测不到这两种酶。与正常动物相比，这些酶在荷肉瘤小鼠的肾脏或肝脏中未受影响。肉瘤中线粒体精氨酸酶II的高活性和表达表明鸟氨酸生成增加。与肌肉相比，肉瘤中鸟氨酸、胍基乙酸和肌酐的水平略有或中度升高。尽管艾氏腹水癌和肉瘤180细胞中肌酸的内在水平较低，但这些细胞能够显著摄取和释放肌酸，这表明存在功能性肌酸转运，通过测量肌酸转运体的mRNA水平得到证实。精氨酸酶II、鸟氨酸脱羧酶、S-腺苷同型半胱氨酸水解酶和甲硫氨酸合成酶的转录水平在肉瘤以及艾氏腹水癌和肉瘤180细胞中显著上调。总体而言，发现与肌酸和精氨酸/甲硫氨酸代谢相关的酶在恶性细胞中显著上调。然而，相同恶性细胞中肌酸激酶的低水平似乎不足以建立有效的肌酸/磷酸肌酸池。L-精氨酸：甘氨酸脒基转移酶和N-胍基乙酸甲基转移酶似乎并非支持肌酸生物合成，而是倾向于支持癌细胞向多胺和甲硫氨酸合成方向的代谢，因为这两种化合物在增殖的癌细胞中需求量很大。
