The identification of transcriptional targets of the tumor suppressor p53 is crucial in understanding mechanisms by which it affects cellular outcomes. Through expression array analysis, we identified cyclooxygenase 2 (Cox‐2), whose expression was inducible by wild‐type p53 and DNA damage. We also found that p53‐induced Cox‐2 expression results from p53‐mediated activation of the Ras/Raf/MAPK cascade, as demonstrated by suppression of Cox‐2 induction in response to p53 by dominant‐negative Ras or Raf1 mutants. Furthermore, heparin‐binding epidermal growth factor‐like growth factor (HB‐ EGF), a p53 downstream target gene, induced Cox‐2 expression, implying that Cox‐2 is an ultimate effector in the p53→HB‐EGF→Ras/Raf/MAPK→Cox‐2 pathway. p53‐induced apoptosis was enhanced greatly in Cox‐2 knock‐out cells as compared with wild‐type cells, suggesting that Cox‐2 has an abrogating effect on p53‐induced apoptosis. Also, a selective Cox‐2 inhibitor, NS‐398, significantly enhanced genotoxic stress‐induced apoptosis in several types of p53+/+ normal human cells, through a caspase‐dependent pathway. Together, these results demonstrate that Cox‐2 is induced by p53‐mediated activation of the Ras/Raf/ERK cascade, counteracting p53‐mediated apoptosis. This anti‐apoptosis effect may be a mechanism to abate cellular stresses associated with p53 induction.

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Acetaminophen is a widely used antipyretic analgesic, reducing fever caused by bacterial and viral infections and by clinical trauma such as cancer or stroke. In rare cases in humans, e.g., in febrile children or HIV or stroke patients, acetaminophen causes hypothermia while therapeutic blood levels of the drug are maintained. In C57͞BL6 mice, acetaminophen caused hypothermia that was dose related and maximum (>2°C below normal) with a dose of 300 mg͞kg. The reduction and recovery of body temperature was paralleled by a fall of >90% and a subsequent rise of prostaglandin (PG)E 2 concentrations in the brain. In cyclooxygenase (COX)-2 ؊/؊ mice, acetaminophen (300 mg͞kg) produced hypothermia accompanied by a reduction in brain PGE 2 levels, whereas in COX-1 ؊/؊ mice, the hypothermia to this dose of acetaminophen was attenuated. The brains of COX-1 ؊/؊ mice had Ϸ70% lower levels of PGE2 than those of WT animals, and these levels were not reduced further by acetaminophen. The putative selective COX-3 inhibitors antipyrine and aminopyrine also reduced basal body temperature and brain PGE 2 levels in normal mice. We propose that acetaminophen is a selective inhibitor of a COX-1 variant and this enzyme is involved in the continual synthesis of PGE 2 that maintains a normal body temperature. Thus, acetaminophen reduces basal body temperature below normal in mice most likely by inhibiting COX-3.

Objective To determine the effects of cyclooxygenase 1 (COX‐1) and COX‐2 gene deletion on collagen‐induced arthritis (CIA). Methods Mice that were susceptible to CIA but lacked either the COX‐1 or the COX‐2 gene were immunized with type II collagen (CII), and the incidence and severity of arthritis were compared with findings in wild‐type animals, by clinical and histologic examination. The immune response was assessed by measuring total CII IgG, IgG1, and IgG2 antibody production in sera from immunized mice. The passive transfer of arthritis, accomplished using anti‐CII monoclonal antibodies, was tested in wild‐type and COX‐deficient (−/−) mice. Splenocytes cultured from CII‐immunized wild‐type and COX−/− mice were challenged with bovine α1(II), and cytokine production was assessed. Results COX‐2 gene deletion reduced the incidence and severity of CIA compared with findings in wild‐type and COX‐1−/− mice. Histologic examination of joints after the onset of clinical arthritis revealed cartilage erosions, proliferation of the synovial lining, and inflammatory cell infiltration in wild‐type and COX‐1−/− mice, but not in COX‐2−/− mice. COX‐2−/− mice exhibited reduced anti‐CII IgG antibody levels, indicating a decreased immune response. However, cytokine production by spleen cells from immunized mice indicated no cytokine deficiencies in COX‐2−/− mice compared with wild‐type or COX‐1−/− mice. More important, arthritis could not be passively transferred to naive COX‐2−/− mice, indicating a requirement for COX‐2 in the pathogenesis of arthritis, independent of the immune response. Conclusion COX‐2−/− mice exhibit at least 2 defects resulting in down‐modulation of the development of CIA: a reduced immune response to CII demonstrated by a markedly reduced antibody titer, and an “inflammatory” defect reflected by the inability to passively transfer arthritis to COX‐2−/− mice.

Prostaglandins formed by cyclooxygenase-1 (COX-1) or COX-2 produce hyperalgesia in sensory nerve endings. To assess the relative roles of the two enzymes in pain processing, we compared responses of COX-1-or COX-2-deficient homozygous and heterozygous mice with wild-type controls in the hot plate and stretching tests for analgesia. Preliminary observational studies determined that there were no differences in gross parameters of behavior between the different groups. Surprisingly, on the hot plate (55°C), the COX-1-deficient heterozygous groups showed less nociception, because mean reaction time was longer than that for controls. All other groups showed similar reaction times. In the stretching test, there was less nociception in COX-1-null and COX-1-deficient heterozygotes and also, unexpectedly, in female COX-2-deficient heterozygotes, as shown by a decreased number of writhes.