The Oncogene of a Human Bladder Carcinoma

This chapter discusses the isolation of three human oncogenes: those of the SW480 colon carcinoma, the HL60 promyelocytic leukemia, and the EJ bladder carcinoma. It focuses on human tumors because of a particular property of human DNA—that is, the presence of highly repeated Alu sequences. These sequences are interspersed in the genome in 300,000 to 500,000 copies per haploid DNA complement. Consequently, one or more of these sequence blocks is usually near, if not within, a chosen human gene. When a human gene is introduced via transfection into a mouse cell, some of these Alu blocks become co-transferred with the scored gene into the recipient. These human Alu blocks are readily distinguished from their mouse counterparts by sequence hybridization. Because of this, the presence of acquired human sequences in the mouse cell can be identified by the use of the “Southern blotting” technique and an Alu-specific sequence probe. Serial passage of a human oncogene through two cycles of transfection into mouse cells creates a particularly simple genetic configuration in the secondary transfectants. The presence of Alu blocks makes possible the molecular cloning of the human DNA sequences. The DNA of a secondary transfectant can be introduced into a lambda phage library, and the human components of the library can be identified once again by using the Alu probe.