Analysis of Thymidine phosphorylase- Uridine phosphorylase double knockout mice

胸腺嘧啶核苷磷酸化酶(TP)是一种参与胸腺嘧啶核苷可逆转化为胸腺嘧啶的酶。在癌症患者和荷瘤动物中，血浆TP水平升高，且在各种实体瘤组织中的表达均高于癌旁非肿瘤组织。茶多酚本身和胸苷的降解产物2-脱氧-D-核糖都具有趋化和血管生成活性，其血管生成活性需要茶多酚的酶活性。TP主要表达于肿瘤的侵袭边缘，其表达与胃癌和结直肠癌的侵袭程度有关，在慢性炎症组织中也有表达。据报道，肿瘤坏死因子α和干扰素γ可诱导TP的表达。为了证实TP的生理作用，我们建立了TP基因缺陷小鼠(TPKO)。TPKO小鼠对单核细胞增多性李斯特菌感染的抵抗力增强。在TPKO中，接种后3天的脾和肝脏的细菌负荷减少了约1logS。TPKO小鼠血浆中干扰素-γ水平升高，而IL-10水平降低。取感染小鼠的肝细胞和脾细胞进行培养。TPKO小鼠条件培养液中IL-10水平明显低于野生型小鼠。IL-10被认为是一种有效的抗炎细胞因子，被认为可以降低肿瘤浸润性淋巴细胞的功能，促进肿瘤的生长。因此，我们试图测试TP在肿瘤逃逸免疫系统中的作用。将年龄和性别匹配的小鼠(野生型和TP-/-)腹腔注射。用1x10^6的EL-4细胞。用EL-4细胞攻击两周后，TPKO小鼠腹水体积的增加和EL-4细胞的生长明显低于野生型小鼠。因此，TP可能使肿瘤逃脱免疫破坏，促进肿瘤生长。

Thymidine phosphorylase (TP) is an enzyme involved in the reversible conversion of thymidine to thymine. In cancer patients and tumor-bearing animals, plasma TP level is elevated, and its expression in various solid tumors is higher than in the adjacent non-neoplastic tissues. Both TP itself and the degradation product of thymidine, 2-deoxy-D-ribose, had chemotactic and angiogenic activities, and the enzymatic activity of TP was required for its angiogenic activity. TP was expressed mainly at the invasive edges of tumors and TP expression was associated with the extent of invasion of gastric and colorectal carcinoma.TP expression was also elevated in chronically inflamed tissues. TNF alpha and IFN gamma are reported to induce TP expression. To confirm the physiological role of TP, we generated mice deficient in TP gene (TPKO). TPKO mice showed an increased resistance to infection by Listeria monocytogenes. Splenic and hepatic bacterial loads 3 days after inoculation were decreased about 1 logs in TPKO. TPKO mice displays increase Interferon gamma level in plasma whereas less level of IL-10. The liver cells and spleen cells were obtained from infected mice, and cultured. The IL-10 levels in the conditioned media of the cells from TPKO mice were significantly less than those from wild-type mice. IL-10 is known to be a potent anti-inflammatory cytokine, and is suggested to reduce the function of tumor infiltrating lymphocytes and contributes the tumor growth. Therefore, we tried to test the role of TP in the escape of tumors from immune systems. Age and sex matched mice (wild-type and TP-/-) were injected i.p. with 1x10^6 of EL-4 cells. Two week after the challenge with EL-4 cells, the increase in volumes of ascites and the growth of EL-4 cells are significantly less in TPKO mice than in wild-type mice. Thus, TP may allow the escape of tumors from immune destruction and contribute the tumor growth.