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Reduced insulin receptor expression and function in human colonic Caco-2 cells by ras and polyoma middle T oncogenes
S Baron-Delage1, J Capeau, V Barbu
1Laboratoire de Biologie Cellulaire, INSERM U.402, Faculté de Médecine Saint-Antoine, Paris, France.
Abstract:
Taking advantage of the potent mitogenic effect exerted by insulin in human colonic cells, we used Caco-2 cells transfected with an activated (Val-12) human Haras gene or the polyoma middle T (PyMT) oncogene, a constitutive activator of pp60c-src tyrosine kinase activity, to investigate the effect of oncogenic p21ras and PyMT/pp60c-src on insulin mitogenic signaling. As compared to vector control Caco-2 cells, both oncogene-transfected cells exhibited: 1) a loss of response to insulin's stimulatory effect on mitogen-activated protein (MAP) kinase activity and cell proliferation, both of which were constitutively increased; 2) a decrease in insulin receptor (IR) affinity and insulin-stimulated exogenous tyrosine kinase activity, which resulted from increased protein kinase C (PKC) activity (Delage, S., Chastre, E., Empereur, S., Wicek, D., Veissiére, D., Capeau, J., Gespach, C., and Cherqui, G. (1993) Cancer Res. 53, 2762-2770), since IR alterations were corrected by PKC down-regulation; and 3) a decrease in both IR mRNA level and IR number, which was independent of PKC since it persisted after PKC down-regulation. In conclusion, this is the first evidence that oncogenic p21ras and PyMT/pp60c-src abolish insulin mitogenic signaling in human colonic cells through mechanisms involving (i) constitutive activation of MAP kinase and (ii) marked decreases in both IR function and expression which are mediated by PKC-dependent and PKC-independent pathways, respectively.
Insights
Oncogenes like Ras and PyMT disrupt insulin signaling in colon cells by activating MAP kinase and reducing insulin receptors through protein kinase C-dependent and independent pathways.
Area of Science:
- Oncology
- Molecular Biology
- Cell Signaling
Background:
- Insulin promotes cell growth in human colon cells.
- Oncogenes like Ras and Polyoma Middle T (PyMT) can alter cell signaling pathways.
- Understanding oncogene effects on insulin signaling is crucial for cancer research.
Purpose of the Study:
- To investigate how oncogenic p21ras and PyMT/pp60c-src affect insulin's mitogenic signaling in human colonic cells.
- To elucidate the specific mechanisms by which these oncogenes interfere with insulin-induced cell proliferation.
Main Methods:
- Utilized Caco-2 cells, a human colon cell line.
- Transfected cells with activated human Haras (Val-12) or PyMT oncogenes.
- Assessed insulin receptor (IR) affinity, MAP kinase activity, and IR mRNA levels.
- Investigated the role of protein kinase C (PKC) in mediating oncogene effects.
Main Results:
- Oncogene-transfected cells showed a loss of response to insulin's mitogenic effects.
- MAP kinase activity and cell proliferation were constitutively increased in oncogene-expressing cells.
- Insulin receptor function and expression were significantly decreased via PKC-dependent and independent pathways.
Conclusions:
- Oncogenic p21ras and PyMT/pp60c-src abolish insulin mitogenic signaling in human colon cells.
- Mechanisms include constitutive MAP kinase activation and reduced insulin receptor function/expression.
- These findings highlight novel pathways by which oncogenes disrupt normal cellular responses to growth factors.