Regulation of epidermal growth factor receptor by activated H-ras and V-myc oncogenes in mouse Balb/3T3 cells: possible roles of AP-1.
We previously reported that introduction of H-ras oncogene decreases the epidermal growth factor (EGF) binding activity to cell surface EGF receptor in mouse Balb/3T3. In this study, we have further isolated four H-ras transfectants, four v-myc transfectants and three both H-ras and v-myc (H-ras/v-myc) transfectants of mouse Balb/3T3 cells. In comparison with introduction of v-myc alone or both H-ras and v-myc oncogene, introduction of H-ras alone resulted in a loss of [125I]EGF binding activity to the cell surface EGF receptor. RT-PCR analysis also showed much lower levels of EGF receptor gene expression in H-ras transfectants compared to that of parental untransformed cells (Balb-Neo1), v-myc and H-ras/v-myc transfectants. Our results demonstrated the activated binding of a transcription factor, Stat1 p84/p91, which directly interacts with EGF receptor, to c-sis-inducible element (SIE) in both v-myc and H-rs/v-myc transfectants, but not in H-ras transfectants. Among transcription factors which we have analysed, activator protein 1 (AP-1) but not SP-1 was modulated by H-ras. Gel shift assays demonstrated the mobility pattern of TPA-responsive element (TRE) binding complex with AP-1 derived from H-ras transfectants migrated faster than those from Balb-Neo1, v-myc and H-ras/v-myc. Expression of c-Jun and Fra-1 was increased more than threefold in H-ras transfectants compared with Balb-Neo1, v-myc and H-ras/v-myc transfectants, but that of c-Fos, Jun B and SP-1 was unchanged. Both transient and permanent expression of H-ras enhanced AP-1 activity in mouse cells, but further co-introduction of dominant negative c-jun mutant encoding a transcriptionally inactive product inhibited the H-ras dependent AP-1 induction. Transfection of the dominant negative c-jun mutant also restored down-regulation of EGF binding by activated H-ras oncogene. Down-regulation of EGf receptor by activated H-ras and the possible involvement of a transcription factor, AP-1 will be discussed.
Okimoto
T
T
Department of Biochemistry, Kyushu University, School of Medicine, Fukuoka, Japan.
Kohno
K
K
Kuwano
M
M
Gopas
J
J
Kung
H F
HF
Ono
M
M
D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation; D004815:Epidermal Growth Factor / Q000378:metabolism; D066246:ErbB Receptors / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic; D016762:Genes, fos / Q000235:genetics; D016259:Genes, myc / Q000235:genetics*; D011905:Genes, ras / Q000235:genetics*; D008077:Lipoproteins, LDL / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D009154:Mutation; D050794:STAT1 Transcription Factor; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000235:genetics*; D014162:Transfection
D004268:DNA-Binding Proteins; D008077:Lipoproteins, LDL; D050794:STAT1 Transcription Factor; C494080:Stat1 protein, mouse; D015534:Trans-Activators; D018808:Transcription Factor AP-1; D004815:Epidermal Growth Factor; D066246:ErbB Receptors