Cell adhesion regulates platelet-derived growth factor-induced MAP kinase and PI-3 kinase activation in stellate cells.
The biologic effects of growth factors are dependent on cell adhesion, and a cross talk occurs between growth factors and adhesion complexes. The aim of the present study was to evaluate the influence of cell adhesion on the major intracellular signaling pathways elicited by platelet-derived growth factor (PDGF) in hepatic stellate cells (HSC). PDGF signaling was investigated in an experimental condition characterized by lack of cell adhesion for different intervals of time. Basal and PDGF-induced focal adhesion kinase (FAK) tyrosine phosphorylation was maintained in a condition of cell suspension for 2, 4, and 6 hours, whereas it was completely lost after 12 and 24 hours. We examined MAP kinase activity at 2 and 24 hours, corresponding to the higher and lower levels of FAK phosphorylation. In these experiments, MAP kinase activity correlated with FAK phosphorylation. Stimulation with PDGF was able to cause Ras-GTP loading only in adherent cells. The ability of PDGF to induce phosphatidylinositol 3-kinase (PI 3-K) activity was abrogated in cells maintained in suspension. The Ser473 phosphorylation of Akt was only marginally affected by the lack of cell adhesion. We then evaluated the association of FAK with c-Src. This association was found to be cell adhesion dependent, and it did not appear to be dependent from phosphorylated FAK. These changes in PDGF-induced intracellular signaling were associated with a remarkable reduction of PDGF-proliferative potential in nonadherent cells, although no marked differences in the apoptotic rate were observed. In conclusion, these results suggest that cell adhesion differentially regulates major signaling pathways activated by PDGF in HSC.
Dipartimento di Medicina Interna and Dipartimento di Fisiopatologia Clinica-Unità di Andrologia, Università degli Studi di Firenze, Florence, Italy.
Vinicio
V
Carloni
Raffaella M S
RM
Defranco
Alessandra
A
Caligiuri
Alessandra
A
Gentilini
Silvia Cappadona
SC
Sciammetta
Elisabetta
E
Baldi
Benedetta
B
Lottini
Paolo
P
Gentilini
Massimo
M
Pinzani
D000081247:CSK Tyrosine-Protein Kinase; D002118:Calcium / Q000378:metabolism; D002448:Cell Adhesion / Q000187:drug effects / Q000502:physiology; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects* / Q000502:physiology; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D051966:Phospholipase C gamma; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism; D010738:Type C Phospholipases / Q000378:metabolism; D014443:Tyrosine / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism; D019061:src-Family Kinases
D000081247:CSK Tyrosine-Protein Kinase; D002118:Calcium; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D007527:Isoenzymes; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D051966:Phospholipase C gamma; D010982:Platelet-Derived Growth Factor; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D017479:Receptors, Platelet-Derived Growth Factor; D010738:Type C Phospholipases; D014443:Tyrosine; D018631:ras Proteins; D019061:src-Family Kinases; C496050:PTK2 protein, human; C000631346:CSK protein, human; C494918:AKT1 protein, human