Dual functionality of cyclooxygenase-2 as a regulator of tumor necrosis factor-mediated G1 shortening and nitric oxide-mediated inhibition of vascular smooth muscle cell proliferation.
BACKGROUND
Cyclooxygenase (COX)-2 contributes to vascular smooth muscle cell (VSMC) proliferation induced by tumor necrosis factor (TNF) and angiotensin II. The present study demonstrates, however, that depending on prevailing conditions, COX-2-derived prostanoids may also inhibit VSMC proliferation.


RESULTS
TNF-alpha stimulated proliferation of VSMCs by shortening the G1 phase of the cell cycle. This effect was abolished by NS-398, a selective COX-2 inhibitor. Addition of TNF did not affect the protein-to-DNA ratio, measured by flow cytometry, suggesting that TNF does not induce VSMC hypertrophy. Inhibition of nitric oxide synthase (NOS) activity attenuated TNF-mediated increases in prostaglandin (PG) I2 synthesis, whereas thromboxane (TX) A2 production and COX-2 protein expression were unaffected. Moreover, inhibition of NOS activity increased TNF-mediated proliferation by approximately 23%. Thus, NO preferentially stimulates PGI2 production, suggesting that production of NO by VSMCs challenged with TNF limits the ability of the cytokine to increase proliferation. NO donors increased COX-2 protein expression and PGI2 synthesis, had no effect on TXA2 production, and decreased cell numbers by 50%, indicating that expression of COX-2 per se might not be sufficient to support proliferation. The effects of NO donors were prevented when COX-2 activity was inhibited with NS-398.


CONCLUSIONS
The COX-2-dependent proliferative response of VSMCs to TNF was modulated in an NO-dependent manner, and PGI2 derived from COX-2 might contribute to the antiproliferative effect of NO donors.
Haider
Asifa
A
New York Medical College, Department of Pharmacology, Valhalla, NY 10595, USA.
Lee
Irene
I
Grabarek
Jerzy
J
Darzynkiewicz
Zbigniew
Z
Ferreri
Nicholas R
NR
D000818:Animals; D018797:Cell Cycle Proteins / Q000378:metabolism; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D019938:Cyclin D1 / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27; D051546:Cyclooxygenase 2; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004247:DNA / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D011464:Epoprostenol / Q000378:metabolism; D016193:G1 Phase / Q000187:drug effects / Q000502:physiology*; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism / Q000502:physiology*; D020030:Nitric Oxide Donors / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism / Q000502:physiology*; D011506:Proteins / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013928:Thromboxane A2 / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology / Q000502:physiology*; D025521:Tumor Suppressor Proteins / Q000378:metabolism
C493962:Cdkn1b protein, rat; D018797:Cell Cycle Proteins; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D020030:Nitric Oxide Donors; D011506:Proteins; D014409:Tumor Necrosis Factor-alpha; D025521:Tumor Suppressor Proteins; D019938:Cyclin D1; D050760:Cyclin-Dependent Kinase Inhibitor p27; D009569:Nitric Oxide; D013928:Thromboxane A2; D004247:DNA; D011464:Epoprostenol; D019001:Nitric Oxide Synthase; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases