Insulin-like growth factor I activates c-Jun N-terminal kinase in MCF-7 breast cancer cells

Endocrinology. 2000 Feb;141(2):544-50. doi: 10.1210/endo.141.2.7307.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Breast Neoplasms
  • Chromones / pharmacology
  • Enzyme Activation / drug effects
  • Enzyme Inhibitors / pharmacology
  • Female
  • Flavonoids / pharmacology
  • Genes, Reporter
  • Humans
  • Insulin-Like Growth Factor I / pharmacology*
  • JNK Mitogen-Activated Protein Kinases
  • Kinetics
  • Mitogen-Activated Protein Kinase 9
  • Mitogen-Activated Protein Kinases / genetics
  • Mitogen-Activated Protein Kinases / metabolism*
  • Morpholines / pharmacology
  • Phosphorylation
  • Protein Kinases / genetics
  • Protein Kinases / metabolism*
  • Tumor Cells, Cultured

Substances

  • Chromones
  • Enzyme Inhibitors
  • Flavonoids
  • Morpholines
  • 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one
  • Insulin-Like Growth Factor I
  • Protein Kinases
  • Mitogen-Activated Protein Kinase 9
  • JNK Mitogen-Activated Protein Kinases
  • Mitogen-Activated Protein Kinases
  • 2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one