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Comparison of intracellular signalling by insulin and the hypermitogenic AspB10 analogue in MCF‐7 breast adenocarcinoma cells
Author(s) -
Oleksiewicz Martin B.,
Bonnesen Christine,
Hegelund Anne Charlotte,
Lundby Anders,
Holm GitteMai Nelander,
Jensen Marianne B.,
Krabbe Jonas S.
Publication year - 2011
Publication title -
journal of applied toxicology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.784
H-Index - 87
eISSN - 1099-1263
pISSN - 0260-437X
DOI - 10.1002/jat.1590
Subject(s) - wortmannin , insulin , phosphorylation , pi3k/akt/mtor pathway , protein kinase b , medicine , biology , insulin receptor , mcf 7 , endocrinology , microbiology and biotechnology , signal transduction , chemistry , cancer cell , insulin resistance , human breast , cancer
We compared mitogenicity and intracellular signalling by human insulin and the AspB10 (X‐10) human insulin analogue in MCF‐7 human mammary adenocarcinoma cells. By flow analysis of phosphorylated histone H3 or cell cycle distributions, insulin and X‐10 were mitogenic at physiologically relevant concentrations (2 n m to 74 p m range), with X‐10 being approximately 3‐fold more mitogenic than insulin. By western blotting with phospho‐specific antibodies, insulin induced phosphorylation of IRS‐1, Akt, p70S6K, S6 ribosomal protein, 4E‐BP1, FoxO3a, FoxO1, p44/42 MAPK and the EGFR. Blocking with wortmannin, rapamycin and U0126 showed that these signalling events conformed to the canonical PI3K pathway. IRS‐1 (Ser302) phosphorylation was abolished by wortmannin and rapamycin, suggesting a feedback from the PI3K pathway on insulin signalling. Compared with equimolar insulin, X‐10 caused up to 2‐fold higher phosphorylation of all proteins examined in this study. The phosphorylation sites that responded most strongly to insulin were not generally the same as those responding most strongly to X‐10. In the PI3K pathway, the most X‐10‐sensitive protein localized to the translation‐regulating arm (p70S6K), with FoxO3a and FoxO1 transcription factors showing a more comparable response to insulin and X‐10. Using flow analysis, we confirmed the correlation between insulin‐triggered translational activation in G0/G1 (S6 phosphorylation) and S‐phase entry by MCF‐7 cells. In summary, our findings implicate asymmetrical PI3K pathway activation and specifically stimulation of protein translation in the hypermitogenic effect of insulin analogues such as X‐10. It remains to be shown whether these findings are relevant to other human mammary cancer cell types. Copyright © 2010 John Wiley & Sons, Ltd.