Stretch-induced retinal vascular endothelial growth factor expression is mediated by phosphatidylinositol 3-kinase and protein kinase C (PKC)-zeta but not by stretch-induced ERK1/2, Akt, Ras, or classical/novel PKC pathways.
Stretch-induced expression of vascular endothelial growth factor (VEGF) is thought to be important in mediating the exacerbation of diabetic retinopathy by systemic hypertension. However, the mechanisms underlying stretch-induced VEGF expression are not fully understood. We present novel findings demonstrating that stretch-induced VEGF expression in retinal capillary pericytes is mediated by phosphatidylinositol (PI) 3-kinase and protein kinase C (PKC)-zeta but is not mediated by ERK1/2, classical/novel isoforms of PKC, Akt, or Ras despite their activation by stretch. Cardiac profile cyclic stretch at 60 cpm increased VEGF mRNA expression in a time- and magnitude-dependent manner without altering mRNA stability. Stretch increased ERK1/2 phosphorylation, PI 3-kinase activity, Akt phosphorylation, and PKC-zeta activity. Signaling pathways were explored using inhibitors of PKC, MEK1/2, and PI 3-kinase; adenovirus-mediated overexpression of ERK, PKC-alpha, PKC-delta, PKC-zeta, and Akt; and dominant negative (DN) mutants of ERK, PKC-zeta, Ras, PI 3-kinase and Akt. Although stretch activated ERK1/2 through a Ras- and PKC classical/novel isoform-dependent pathway, these pathways were not responsible for stretch-induced VEGF expression. Overexpression of DN ERK and Ras had no effect on VEGF expression in these cells. In contrast, DN PI 3-kinase as well as pharmacologic inhibitors of PI 3-kinase blocked stretch-induced VEGF expression. Although stretch-induced PI 3-kinase activation increased both Akt phosphorylation and activity of PKC-zeta, VEGF expression was dependent on PKC-zeta but not Akt. In addition, PKC-zeta did not mediate stretch-induced ERK1/2 activation. These results suggest that stretch-induced expression of VEGF involves a novel mechanism dependent upon PI 3-kinase-mediated activation of PKC-zeta that is independent of stretch-induced activation of ERK1/2, classical/novel PKC isoforms, Ras, or Akt. This mechanism may play a role in the well documented association of concomitant hypertension with clinical exacerbation of neovascularization and vascular permeability.
Suzuma
Izumi
I
Research Division and Beetham Eye Institute, Joslin Diabetes Center, Boston, Massachusetts 02215, USA.
Suzuma
Kiyoshi
K
Ueki
Kohjiro
K
Hata
Yasuaki
Y
Feener
Edward P
EP
King
George L
GL
Aiello
Lloyd Paul
LP
D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D016228:Endothelial Growth Factors / Q000235:genetics / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008222:Lymphokines / Q000235:genetics / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D020033:Protein Isoforms / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D020871:RNA Stability; D017479:Receptors, Platelet-Derived Growth Factor / Q000378:metabolism; D012160:Retina / Q000737:chemistry / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D013314:Stress, Mechanical; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D018631:ras Proteins; D000099221:Protein Kinase C zeta
D016228:Endothelial Growth Factors; D004791:Enzyme Inhibitors; D008222:Lymphokines; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D020033:Protein Isoforms; D011493:Protein Kinase C; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D017479:Receptors, Platelet-Derived Growth Factor; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D018631:ras Proteins; D000099221:Protein Kinase C zeta