Induction of cyclo‐oxygenase‐2 in human endothelial cells by SIN‐1 in the absence of prostaglandin production

Nitric oxide (NO) regulates cyclo‐oxygenase (COX) activity in various cell systems and reports conflict in regard to its stimulatory versus inhibitory role. Incubation of human umbilical vein endothelial cells (HUVEC) with SIN‐1 (3‐morpholinosydnonimine), a donor of NO, resulted in a rapid and dose‐dependent increase in the expression of COX‐2 as analysed by Western and Northern blotting. Incubation of HUVEC with SIN‐1 and interleukine (IL)‐1α resulted in increased induction of COX‐2 compared with IL‐1α alone and corresponded to an additive effect. The COX‐2 induction was dependent on a de novo synthesis since cycloheximide, an inhibitor of protein synthesis, blocked the enzyme expression. The increase in COX‐2 expression was not accompanied by a corresponding change in prostaglandin (PG) production. However, the COX activity was partially recovered when immunoprecipitated COX‐2 was incubated with arachidonic acid and haematin. Peroxynitrite, a highly reactive nitrogen molecule derived from the interaction of NO and superoxide anion, significantly increased COX‐2 expression. Under these conditions and within the limit of detection of the antibody, selective antibody for nitrotyrosine failed to detect nitrated COX‐2 in immunoprecipitated COX‐2 when cells where incubated with SIN‐1 or SIN‐1+IL‐1α. Ro 31‐8220, a specific inhibitor of protein kinase (PK) C, blocked the induction of COX‐2. Also, SB203580, the selective inhibitor of p38 MAP kinase, strongly blocked the induction of COX‐2 by SIN‐1 in the presence or absence of IL‐1α, whereas the MEK‐1 inhibitor, PD 98059, affected it to a lesser extent. These data demonstrate that SIN‐1 induces COX‐2 in HUVEC in the absence of PG formation and suggest a complex regulation of COX‐2 expression and PG formation by NO in endothelial cells.British Journal of Pharmacology (2001) 133 , 1163–1171; doi: 10.1038/sj.bjp.0704163