Mechanisms of ANG II-induced mitogenic responses: role of 12-lipoxygenase and biphasic MAP kinase.
The potential mechanisms of angiotensin II (ANG II)-induced mitogenesis were studied in a Chinese hamster ovary fibroblast cell line overexpressing the rat vascular type 1a ANG II receptor (CHO-AT1a). ANG II had potent mitogenic effects in these CHO-AT1a cells, leading to a sustained increase in cell number as well as a dose-dependent increase in DNA synthesis. ANG II treatment also induced a biphasic elevation of mitogen-activated protein (MAP) kinase activity of both p42MAPK and p44MAPK with a rapid early peak at 5 min (2- to 6-fold) followed by a second sustained increase that reached a peak at 3 h (1.5- to 3-fold). We have previously shown that the 12-lipoxygenase (12-LO) pathway of arachidonate metabolism plays a key role in ANG II-induced growth of vascular smooth muscle and adrenal cells. In the present study, ANG II (10(-7) M) increased the formation of the 12-LO product, 12-hydroxyeicosatetraenoic acid (12-HETE). ANG II-induced DNA synthesis was inhibited by a specific LO inhibitor, cinnamyl-3,4-dihydroxy-alpha-cyanocinnamate (CDC, 10 microM). In contrast, a cyclooxygenase blocker of arachidonate metabolism such as ibuprofen had no effect on ANG II-induced DNA synthesis. ANG II-induced DNA synthesis was also partially (32%) blocked by pertussis toxin (PTX). CDC and PTX also selectively blocked only the late (3 h) peak of ANG II-induced MAP kinase activity, suggesting that the late sustained peak of MAP kinase activity may be linked to the mitogenic effect of ANG II. Direct addition of 12-HETE (10(-7) M) led to a sustained increase in cell number similar to the effect of ANG II. 12-HETE also caused an increase in MAP kinase activity, and 12-HETE effects were blocked by PTX. These results suggest that ANG II-induced mitogenic response is associated with sustained MAP kinase activation and that LO activation may play a key role in this process.
Wen
Y
Y
Department of Diabetes, Endocrinology and Metabolism, City Of Hope Medical Center, Duarte, California 91010, USA.
Nadler
J L
JL
Gonzales
N
N
Scott
S
S
Clauser
E
E
Natarajan
R
R
D019377:12-Hydroxy-5,8,10,14-eicosatetraenoic Acid / Q000502:physiology; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D001092:Arachidonate 12-Lipoxygenase / Q000502:physiology*; D016466:CHO Cells; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000502:physiology*; D006224:Cricetinae; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004247:DNA / Q000096:biosynthesis; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000502:physiology; D007052:Ibuprofen / Q000494:pharmacology; D008469:Meclofenamic Acid / Q000494:pharmacology; D008938:Mitosis / Q000187:drug effects*; D037342:Pertussis Toxin; D013997:Time Factors; D014162:Transfection; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D016861:Cyclooxygenase Inhibitors; D010566:Virulence Factors, Bordetella; D000804:Angiotensin II; D008469:Meclofenamic Acid; D019377:12-Hydroxy-5,8,10,14-eicosatetraenoic Acid; D004247:DNA; D001092:Arachidonate 12-Lipoxygenase; D037342:Pertussis Toxin; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019204:GTP-Binding Proteins; D007052:Ibuprofen