Rivkina M B, Cullen J M, Robinson W S, Marion P L
Department of Medicine, Stanford University School of Medicine, California 94305.
Cancer Res. 1994 Oct 15;54(20):5430-7.
Infection with hepadnaviruses and exposure to dietary aflatoxin are considered major risk factors in the development of hepatocellular carcinoma (HCC) both in humans and in animals. Recently, a broad range of mutations in the p53 tumor suppressor gene has been reported in human HCCs, predominantly from hepatitis B virus carriers in areas with either high or low levels of exposure to dietary aflatoxin. To determine whether p53 mutations are common to HCCs of hosts infected with related hepadnaviruses with and without treatment with aflatoxin, we studied the occurrence of mutations in the p53 gene in HCCs of ground squirrels and woodchucks with history of infection with ground squirrel hepatitis virus (GSHV) and woodchuck hepatitis virus, respectively. Sequencing of wild type p53 genes from ground squirrels and woodchucks revealed remarkable homology between the two species with only a few amino acid differences in exons 4, 8, and 9. Using direct polymerase chain reaction sequencing, we analyzed the state of the p53 gene (exons 4-9) in 20 HCCs from ground squirrels (2 uninfected, 7 with past, and 11 with ongoing infection with GSHV) and in 11 HCCs from woodchucks persistently infected with woodchuck hepatitis virus. Five GSHV carrier and two uninfected ground squirrels received i.p. administration of aflatoxin B1. We detected only one mutation in the p53 gene of the tested animals. This mutation was located in codon 176 of exon 5 in the HCC of a GSHV-positive ground squirrel treated with aflatoxin. Mutation was caused by a G to T transversion in the second position of the codon, resulting in the replacement of cysteine with phenylalanine, and was accompanied by a tumor-specific loss of heterozygosity. p53 allelic amino acid variation with sequences coding for aspartic acid or asparagine was present in codon 61 in the variable region of exon 4 in both HCCs and nonneoplastic tissues of ground squirrels. In view of the considerably lower apparent rate of mutations in comparison to human HCCs, we suggest a less important role for aflatoxin in the induction of p53 mutations in HCCs of ground squirrels. Alternatively, etiological factors other than p53 mutations may be of greater significance in the development of HCC in ground squirrels and woodchucks.
感染嗜肝DNA病毒和接触膳食黄曲霉毒素被认为是人类和动物肝细胞癌（HCC）发生发展的主要危险因素。最近，在人类肝癌中报道了p53肿瘤抑制基因广泛的突变，主要来自黄曲霉毒素暴露水平高或低地区的乙肝病毒携带者。为了确定p53突变对于感染相关嗜肝DNA病毒且有或无黄曲霉毒素处理的宿主的肝癌是否常见，我们分别研究了有地松鼠肝炎病毒（GSHV）感染史的地松鼠和有土拨鼠肝炎病毒感染史的土拨鼠肝癌中p53基因的突变情况。对地松鼠和土拨鼠野生型p53基因进行测序，发现这两个物种之间有显著的同源性，仅在第4、8和9外显子中有少数氨基酸差异。使用直接聚合酶链反应测序，我们分析了20例地松鼠肝癌（2例未感染，7例既往感染，11例正在感染GSHV）和11例持续感染土拨鼠肝炎病毒的土拨鼠肝癌中p53基因（第4 - 9外显子）的状态。5只GSHV携带者和2只未感染的地松鼠接受了腹腔注射黄曲霉毒素B1。我们在受试动物的p53基因中仅检测到1个突变。该突变位于一只接受黄曲霉毒素处理的GSHV阳性地松鼠肝癌第5外显子的176密码子处。突变是由密码子第二位的G到T颠换引起的，导致半胱氨酸被苯丙氨酸取代，并伴有肿瘤特异性杂合性缺失。在第4外显子可变区的61密码子中，地松鼠的肝癌组织和非肿瘤组织中均存在编码天冬氨酸或天冬酰胺的p53等位氨基酸变异。鉴于与人类肝癌相比，明显的突变率要低得多，我们认为黄曲霉毒素在诱导地松鼠肝癌p53突变中的作用较小。或者，除p53突变外的其他病因因素在地松鼠和土拨鼠肝癌的发生发展中可能具有更大的意义。
