Malignant Transformation of Mouse BALB / 3 T 3 Cells by Polyoma Middle T Antigen Requires Epidermal

The mouse cell line MO-5, which is defective in receptor-binding activity of epidermal growth factor (EGF), is very poorly transformed by polyoma middle I antigen or v-src gene, but activated c-H-ras and v-mos gene can induce the transformation (M. Ono, M. Yakushinji, K. Segawa, and M. Kuwano, Mol. Cell. Biol., 8: 4i90-4i96, 1988). We established clones of MO-S expressing a functional EGF receptor (EGF-R) after introduction of the human EGF-R complementary DNA into MO-5 (MNER23 and MNER31), and we also established a clone (BNER4) expressing human EGF-R from the parental cell line, BALB/313. MNER23, MNER3i, and BNER4 expressed EGF-R activity at about 2to 6-fold higher levels than did control BALB/3T3 cells. A marked increase in DNA synthesis in response to [GF was observed in these BNER4, MNER23, and MNER31 cell lines compared to BALB/3T3 cells; however, there was little if any increase in DNA synthesis of MO-S in the presence of EGF. Introduction of the polyoma middle I antigen gene into BALB/313, BNER4, MNER23, and MNER3i resulted in the appearance of transformation foci, but MO-S again showed little response. We purified clones B4-mT-2, M23-mT-i, M23-mT-2, M23-mT-3, and M3i-mT-i3 from transformation foci of BNER4, MNER23, and MNER31 cells, which were respectively transfected with the middle I antigen. All of the middle I antigenpositive transfectants demonstrated abilities to form both colonies in soft agar and tumors in nude mice. The presence of EGF-R appears to be indispensable for malignant transformation by polyoma middle I antigen.