Objective: LAPTM4B-35 protein is one of the isoforms that are encoded by a cancer driver gene, LAPTM4B. This gene was primarily found and identified in our lab of Peking University School of Basic Medical Sciences. The LAPTM4B-35 protein and its encoded mRNA are significantly over-expressed in a variety of cancers, such as hepatocellular carcinoma (HCC), lung cancers (including non small-cell lung cancer and small-cell lung cancer), stomach cancer, colorectal carcinoma, pancreatic cancer, gallbladder cancer, cholangiocarcinoma, breast cancer, prostate cancer, ovarian cancer, cervical cancer, endometrial cancer, and so on. It has firmly demonstrated through lab experiments either in vivo or in vitro, as well as clinical studies that the over-expression of LAPTM4B-35 can promote cancer growth, metastasis, and multidrug resistance. Specially, the expressive level of LAPTM4B-35 is associa-ted with recurrence of HCC. The aim of this study is to identify the release of LAPTM4B-35 protein from hepatocellular carcinoma into blood of HCC patients and into the medium of cultured HCC cells, and to identify its possible form of LAPTM4B-35 protein existed in blood and cell culture medium, as well as to explore the possibility of LAPTM4B-35 protein as a novel HCC biomarker for diagnosis of HCC and prognosis of HCC patients.
Methods: Immunobloting (Western blot) and enzyme-linked immunosorbent assay (ELISA) were used for identification of LAPTM4B-35 protein in the blood of HCC patients and normal individuals. Ultrafiltration and ultracentrifugation were used to isolate and purify exosomes from the culture medium of HCC cells.
Results: LAPTM4B-35 protein existed in the blood from HCC patients and normal donors that were demonstrated through Western blot and ELISA. LAPTM4B-35 was also released into the culture medium of HCC cells in the form of exosomes. Preliminary experiments showed that the average and the median of LAPTM4B-35 protein level in the blood of HCC patients (n=43) were both significantly higher than that in the blood of normal donors (n=33) through sandwich ELISA.
Conclusion: It is promising that the LAPTM4B-35 protein which is released from HCC cells in the form of exosomes into their extraenvironment may be exploited as a novel cancer biomarker for HCC serological diagnosis.
目的: LAPTM4B-35是北京大学基础医学院发现和鉴定的一个肿瘤驱动基因LAPTM4B所编码的蛋白质同型分子(isoform)之一，其在多种恶性肿瘤中[如肝癌、肺癌(包括非小细胞肺癌和小细胞肺癌)、胃癌、结直肠癌、胰腺癌、胆囊癌、胆管癌、乳腺癌、前列腺癌、宫颈癌、子宫内膜癌等]均超高表达。实验室和临床资料均证明，LAPTM4B-35蛋白的过表达促进肿瘤生长、转移和多药耐药，LAPTM4B-35的蛋白表达水平与肝癌的复发相关。本文的目的在于鉴定患者体内的肝癌细胞和体外培养的肝癌细胞系是否释放出LAPTM4B-35蛋白到血液和细胞培养液中，以及其可能的存在形式，为建立肝细胞癌等肿瘤的血清学诊断新方法奠定基础。
方法: 采用免疫印迹分析(Western blot)、酶联免疫吸附实验(enzyme-linked immunosorbent assay，ELISA)鉴定LAPTM4B-35蛋白，应用超滤和超离心方法从肝癌细胞培养上清液中分离、纯化外排体(exosome)。
结果: 特异性抗体的ELISA结果表明，肝细胞癌患者的血液中存在LAPTM4B-35蛋白，体外培养的肝癌细胞以外排体形式释放LAPTM4B-35蛋白到培养基的上清液中。ELISA夹心法检测表明，肝细胞癌患者(n=43)血淸中LAPTM4B-35蛋白的平均水平和中位值均显著高于正常人(n=33)。
结论: 肝癌细胞以外排体形式释放到其外环境中的LAPTM4B-35蛋白有望成为肝细胞癌血清学诊断的新标志物。
Keywords: Biomarkers, tumor; Exosomes; Hepatocellular carcinoma; LAPTM4B-35.