Insulin-like growth factor I activates c-Jun N-terminal kinase in MCF-7 breast cancer cells.
Insulin-like growth factor I (IGF-I) is an important mediator of breast cancer cell growth, although the signaling pathways important for IGF-I-mediated effects in breast cancer cells are still being elucidated. We had demonstrated previously that increased intracellular cAMP in MCF-7 breast cancer cells inhibited cell growth and IGF-I-induced gene expression, as determined using a reporter gene assay. This effect of cAMP on IGF-I signaling was independent of IGF-I-induced activation of the mitogen-activated protein kinases extracellular signal-regulated kinases 1 and 2 (ERK1 and -2). To determine whether this effect of cAMP may be mediated via another mitogen-activated protein kinase, the ability of IGF-I to activate the c-Jun N-terminal kinases (JNKs) was investigated. Treatment of MCF-7 cells with 100 ng/ml IGF-I increased the level of phosphorylated JNK, as determined by Western blot analysis. JNK phosphorylation was not evident until 15 min after treatment with IGF-I, and peak levels of phosphorylation were present at 30-60 min. This was in contrast to ERK phosphorylation, which was present within 7.5 min of IGF-I treatment. Determination of JNK activity using an immune complex assay demonstrated a 3.3- and 3.5-fold increase in JNK1 and -2 activity, respectively, 30 min after treatment with 100 ng/ml IGF-I. The use of PD98059, which inhibits activation of ERK1 and -2, and LY 294002, an inhibitor of phosphatidylinositol 3-kinase, demonstrated that IGF-I-induced activation of JNK1 is independent of ERK and phosphatidylinositol 3-kinase activation. In contrast, increasing intracellular cAMP with forskolin resulted in abrogation of IGF-I-induced JNK activity. In summary, these data demonstrate that IGF-I activates the JNKs in MCF-7 breast cancer cells and, taken together with the results of our previous study, suggest that JNK may contribute to IGF-I-mediated gene expression and, possibly, cell growth in MCF-7 breast cancer cells.
Monno
S
S
Center for Endocrinology, Metabolism, and Molecular Medicine, Department of Medicine, Veterans Administration Chicago Healthcare System-Lakeside Division and Northwestern University Medical School, Illinois 60611, USA.
Newman
M V
MV
Cook
M
M
Lowe
W L
WL
D001943:Breast Neoplasms; D002867:Chromones / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005419:Flavonoids / Q000494:pharmacology; D017930:Genes, Reporter; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D048031:JNK Mitogen-Activated Protein Kinases; D007700:Kinetics; D048056:Mitogen-Activated Protein Kinase 9; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D009025:Morpholines / Q000494:pharmacology; D010766:Phosphorylation; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D002867:Chromones; D004791:Enzyme Inhibitors; D005419:Flavonoids; D009025:Morpholines; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D007334:Insulin-Like Growth Factor I; D011494:Protein Kinases; D048056:Mitogen-Activated Protein Kinase 9; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one