Induction of AP-1 activity associated with c-Jun and JunB is required for mitogenesis induced by insulin and vanadate in SV40-transformed 3T3T cells.
Insulin and vanadate function as complete mitogens for SV40-transformed murine 3T3T (CSV3-1) cells but not for nontransformed 3T3T cells. Mitogenesis induced by insulin and vanadate in CSV3-1 cells is associated with the induction of the expression of protooncogenes c-jun and junB, two major AP-1 transcription factor components. We now report that both insulin and vanadate induce a significant increase in AP-1 DNA binding activity in CSV3-1 cells but not in 3T3T cells. Gel supershift assays and Western blot analysis using specific antibodies demonstrate that the increased AP-1 binding activity induced by insulin and vanadate in CSV3-1 cells is primarily contributed by an increase in the expression of c-Jun and JunB protein levels. Furthermore, treatment of CSV3-1 cells with antisense oligodeoxyribonucleotides to c-jun or to junB blocks insulin- and vanadate-induced mitogenesis whereas antisense junD oligomers have no inhibitory effects. These results therefore demonstrate that the induction of AP-1 binding activity associated with c-Jun and JunB is required for insulin- and vandate-induced mitogenesis in SV40-transformed murine 3T3T cells. Additional data presented in this paper show that JunD/AP-1 binding activity, which is thought to play a negative role in regulating cell proliferation, is also slightly induced following insulin and vanadate stimulation in CSV3-1 cells. Nevertheless, the ratio of proliferation promoting c-Jun/AP-1 and JunB/AP-1 binding activities to proliferation inhibiting JunD/AP-1 binding activity is significantly increased following insulin and vanadate stimulation. These results therefore support the concept that modulation of the balance of positive Jun/AP-1 and negative Jun/AP-1 activities is important in regulating cell proliferation.
Wang
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Department of Pathology, University of Tennessee College of Medicine, Memphis 38163, USA.
Xie
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Scott
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D016475:3T3 Cells; D000818:Animals; D002461:Cell Line, Transformed; D007328:Insulin / Q000494:pharmacology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008938:Mitosis / Q000187:drug effects*; D016755:Proto-Oncogene Proteins c-jun / Q000096:biosynthesis / Q000378:metabolism*; D013539:Simian virus 40 / Q000502:physiology*; D014638:Vanadates / Q000494:pharmacology*
D007328:Insulin; D016755:Proto-Oncogene Proteins c-jun; D014638:Vanadates