c-erbB2-induced disruption of matrix adhesion and morphogenesis reveals a novel role for protein kinase B as a negative regulator of alpha(2)beta(1) integrin function.
Overexpression of the growth factor receptor subunit c-erbB2, leading to its ligand-independent homodimerization and activation, has been implicated in the pathogenesis of mammary carcinoma. Here, we have examined the effects of c-erbB2 on the adhesive properties of a mammary epithelial cell line, HB2/tnz34, in which c-erbB2 homodimerization can be induced by means of a transfected hybrid "trk-neu" construct. trk-neu consists of the extracellular domain of the trkA nerve growth factor (NGF) receptor fused to the transmembrane and cytoplasmic domains of c-erbB2, allowing NGF-induced c-erbB2 homodimer signaling. Both spreading and adhesion on collagen surfaces were impaired on c-erbB2 activation in HB2/tnz34 cells. Antibody-mediated stimulation of alpha(2)beta(1) integrin function restored adhesion, suggesting a direct role for c-erbB2 in integrin inactivation. Using pharmacological inhibitors and transient transfections, we identified signaling pathways required for suppression of integrin function by c-erbB2. Among these was the MEK-ERK pathway, previously implicated in integrin inactivation. However, we could also show that downstream of phosphoinositide-3-kinase (PI3K), protein kinase B (PKB) acted as a previously unknown, potent inhibitor of integrin function and mediator of the disruptive effects of c-erbB2 on adhesion and morphogenesis. The integrin-linked kinase, previously identified as a PKB coactivator, was also found to be required for integrin inactivation by c-erbB2. In addition, the PI3K-dependent mTOR/S6 kinase pathway was shown to mediate c-erbB2-induced inhibition of adhesion (but not spreading) independently of PKB. Overexpression of MEK1 or PKB suppressed adhesion without requirement for c-erbB2 activation, suggesting that these two pathways partake in integrin inhibition by targeting common downstream effectors. These results demonstrate a major novel role for PI3K and PKB in regulation of integrin function.
Department of Medical Biochemistry, University of Göteborg, Sweden.
Lachmi E
LE
Lindberg
Shahram
S
Hedjazifar
Dan
D
Baeckström
D000818:Animals; D002448:Cell Adhesion / Q000502:physiology*; D002460:Cell Line; D024042:Collagen Type I / Q000378:metabolism; D019281:Dimerization; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D005109:Extracellular Matrix / Q000378:metabolism*; D005260:Female; D017930:Genes, Reporter; D006801:Humans; D038982:Integrin alpha2beta1 / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000502:physiology; D008321:Mammary Glands, Animal / Q000166:cytology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009024:Morphogenesis; D020932:Nerve Growth Factor / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D020917:Receptor, trkA / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases
D024042:Collagen Type I; D004791:Enzyme Inhibitors; D038982:Integrin alpha2beta1; D020928:Mitogen-Activated Protein Kinases; D020932:Nerve Growth Factor; D019869:Phosphatidylinositol 3-Kinases; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D018719:Erb-b2 Receptor Tyrosine Kinases; D020917:Receptor, trkA; D011993:Recombinant Fusion Proteins; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; C546842:MTOR protein, human