Oncogene-induced up-regulation of Caco-2 cell proliferation involves IGF-II gene activation through a protein kinase C-mediated pathway.
We previously reported that ras and polyoma middle T (PyMT), a constitutive activator of the src protooncogene product, up-regulated Caco-2 cell proliferation along with protein kinase C (PKC) alpha expression and PKC activity. We aimed to investigate whether oncogene-induced up-regulation of Caco-2 cell proliferation involved stimulation of the autocrine IGF-II/IGF-I receptor (IGFIR) loop described in these cells and if so, to analyse the role of overexpressed and activated PKC. Compared with control vector transfected Caco-2 cells, ras- and PyMT-transfected cells exhibited increased expression of the 6.0 and 4.8 kb IGF-II transcripts. This was due to increased activity of the P3 and P4 promoters of the IGF-II gene which correlated with increased expression and DNA-binding activity of Sp1, a transcription factor interacting with several specific sites in P3 and P4 promoters. Oncogene-transfected cells displayed enhanced autocrine IGF-II production, which was fully responsible for the oncogene-induced increase in their proliferation since this increase was blunted by anti-human IGF-II and IGF1R (alphaIR3) antibodies. PKC mediated oncogene activation of the IGF-II gene presumably through action on Sp1 since (i) PKC activation by phorbol 12-myristate 13-acetate increased Sp1 expression, P3 and P4 activity and IGF-II mRNA in control but not in oncogene-transfected cells; and (ii) PKC inhibition by the PKC inhibitor Gö6976 reduced Sp1, P3 and P4 activity and IGF-II mRNA in all three cell lines. This is the first evidence that ras- and PyMT/src oncogenes up-regulate Caco-2 cell proliferation through a PKC-mediated pathway which stimulates IGF-II gene transcription and thereby increases autocrine IGF-II production. The mechanisms underlying IGF-II gene activation by PKC most probably involve action on Sp1.
INSERM U.402, Laboratoire de Biologie Cellulaire, Faculté de Médecine Saint-Antoine, Paris, France.
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Cadoret
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Baron-Delage
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Bertrand
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Kornprost
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Groyer
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Gespach
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Capeau
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Cherqui
D000911:Antibodies, Monoclonal / Q000494:pharmacology; D000952:Antigens, Polyomavirus Transforming / Q000096:biosynthesis / Q000235:genetics*; D018938:Caco-2 Cells; D002455:Cell Division / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic; D011905:Genes, ras; D006801:Humans; D018969:Insulin-Like Growth Factor Binding Proteins / Q000096:biosynthesis / Q000235:genetics; D007335:Insulin-Like Growth Factor II / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology; D009857:Oncogenes; D011493:Protein Kinase C / Q000378:metabolism*; D017526:Receptor, IGF Type 1 / Q000502:physiology; D015398:Signal Transduction; D016329:Sp1 Transcription Factor / Q000235:genetics / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection
D000911:Antibodies, Monoclonal; D000952:Antigens, Polyomavirus Transforming; D018969:Insulin-Like Growth Factor Binding Proteins; D016329:Sp1 Transcription Factor; D007335:Insulin-Like Growth Factor II; D017526:Receptor, IGF Type 1; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate