Although the cardioprotection of late preconditioning (PC) is known to be mediated by both inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2), the signaling mechanism responsible for COX-2 upregulation and the interaction between iNOS and COX-2 remain unknown. A total of 122 mice were used to address this issue. In wild-type mice preconditioned with six cycles of 4-min coronary occlusion-4-min reperfusion, ischemic PC resulted in rapid activation of nuclear STAT1/3 through tyrosine phosphorylation (STAT1: 339 +/- 48% of control; STAT3: 389 +/- 46% of control) and increased STAT1/3-DNA binding activity (687 +/- 58% of control) at 30 min after PC, with subsequent upregulation of COX-2 protein (373 +/- 60% of control) and activity(increased myocardial levels of PGE2, PGF(2alpha), and 6-keto-PGF(1alpha)) at 24 h. However, COX-1 protein was not changed 24 h after ischemic PC. Pretreatment with the Janus tyrosine kinase (JAK) inhibitor AG-490 before the six occlusion-reperfusion cycles blocked both the tyrosine phosphorylation of STAT1/3 and the subsequent upregulation of COX-2 protein, demonstrating a necessary role of the JAK-STAT pathway in the induction of COX-2. Targeted disruption of the iNOS gene (iNOS-/-) did not block the increased expression of COX-2 protein 24 h after ischemic PC but completely blocked the increase in COX-2 activity, whereas targeted disruption of the COX-2 gene (COX-2-/-) did not alter ischemic PC-induced iNOS induction. Immunoprecipitation of preconditioned heart tissues with anti-COX-2 antibodies followed by immunoblotting with anti-iNOS antibodies revealed that the increased iNOS protein co-precipitated with COX-2. We conclude that (i) the upregulation of COX-2 protein expression after ischemic PC is mediated by a JAK1/2-STAT1/3-signaling cascade; (ii) COX-2 activity requires upregulated iNOS and iNOS-derived NO; and (iii) COX-2 forms complexes with iNOS, supporting a direct interaction between these two proteins. To our knowledge, this is the first evidence that myocardial COX-2 is upregulated via a JAK1/2-STAT1/3 pathway.