The role of phosphatidylinositol 3'-kinase and its downstream signals in erbB-2-mediated transformation.
We previously demonstrated that erbB-2-overexpressing human mammary epithelial (HME) cells exhibit several transformed phenotypes including growth factor independence, anchorage-independent growth, motility, and invasiveness. Because phosphatidylinositol 3'-kinase (PI3K) is a major target of erbB-2 activation, we tested the contribution that PI3K and its downstream signaling pathways make to these phenotypes. Utilizing a constitutively active form of PI3K, p110CAAX, we show that PI3K can mediate most phenotypes observed in erbB-2-overexpressing cells. To identify pathways leading from PI3K to specific phenotypes, we expressed constitutively active AKT or PTEN in erbB-2-overexpressing cells or in HME cells. HME cells expressing constitutively active AKT were growth factor independent, anchorage independent and motile, but not invasive. PTEN expression blocked erbB-2-mediated invasion but none of the other phenotypes. Rottlerin blocked invasion induced by p110CAAX and erbB-2, suggesting that protein kinase C delta (PKC-delta) is the downstream effector of PI3K responsible for the invasive capacity of the cells. Consistent with these observations, phospho-AKT remained detectable in erbB-2 cells treated with LY294002 or expressing exogenous PTEN, but was abolished by treatment with the p38MAP kinase inhibitor SB202190. Thus, both PI3K-dependent and p38MAP kinase-dependent pathways lead to activation of AKT, and activation of PKC-delta, via PI3K, mediates invasion.
Woods Ignatoski
Kathleen M
KM
Department of Radiation Oncology and the Comprehensive Cancer Center, University of Michigan Health Systems, 1500 E. Medical Center Drive, Ann Arbor, MI 48109-0948, USA.
Livant
Donna L
DL
Markwart
Sonja
S
Grewal
Navdeep K
NK
Ethier
Stephen P
SP
D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D002633:Chemotaxis; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D010587:Phagocytosis; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D011725:Pyridines / Q000494:pharmacology; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D014162:Transfection; D014407:Tumor Cells, Cultured
D004791:Enzyme Inhibitors; D007093:Imidazoles; D019869:Phosphatidylinositol 3-Kinases; D011725:Pyridines; D018719:Erb-b2 Receptor Tyrosine Kinases; C090942:4-(4-fluorophenyl)-2-(4-hydroxyphenyl)-5-(4-pyridyl)imidazole