Higher animals including man each carry approximately 100,000 genes, but only about 15% thereof is expressed, and characteristics of individual's biological process, e.g., genesis, differentiation, homeostasis, responses to stimuli, control of cell cycle, aging and apoptosis (programmed cell death), are determined depending on which genes are expressed (Liang, P. and A. B. Pardee, Science, 257: 967-971 (1992)).
Pathogenic phenomena such as tumorigenesis are caused by gene mutation which brings about changes in the mode of gene expression.
It has been reported that tumorigenesis is caused by various genetic changes such as the loss of chromosomal heterozygosity, activation of oncogenes and inactivation of tumor suppressor genes, e.g., p53 gene (Bishop, J. M., Cell, 64, 235-248 (1991); and Hunter, T., Cell, 64, 249-270 (1991)). Further, it has been reported that 10 to 30% of human cancer arises from the activation of oncogene through amplification of protooncogenes.
Therefore, the activation of protooncogenes plays an important role in the etiology of many tumors and there has existed a need to identify protooncogenes.
The present inventor reported that a protooncogene, human cervical cancer 1 (HCCR-1), is specifically overexpressed in cancer cells (Korean Patent Laid-open Publication No. 2001-39566). In order to unravel the mechanism involved in the tumorigenesis, the present inventor has endeavored to prepare a cancer cell line and a transgenic mammal developing cancer using HCCR-1 protooncogene.