The expression of cPLA2 is critical for transformed growth of non-small cell lung cancer (NSCLC). It is known that phorbol 12-myristate 13-acetate (PMA)-activated signal transduction pathway is thought to be involved in the oncogene action in NSCLC and enzymatic activation of cPLA2. However, the transcriptional regulation of cPLA2α in PMA-activated NSCLC is not clear. In this study, we found that PMA induced the mRNA level and protein expression of cPLA2α. In addition, two Sp1-binding sites of cPLA2α promoter were required for response to PMA and c-Jun overexpression. Small interfering RNA (siRNA) of c-Jun and nucleolin inhibited PMA induced the promoter activity and protein expression of cPLA2α. Furthermore, PMA stimulated the formation of c-Jun/Sp1 and c-Jun/nucleolin complexes as well as the binding of these transcription factor complexes to the cPLA2α promoter. Although Sp1-binding sites were required for the bindings of Sp1 and nucleolin to the promoter, the binding of nucleolin or Sp1 to the promoter was independent of each other. Our results revealed that c-Jun/nucleolin and c-Jun/Sp1 complexes play an important role in PMA-regulated cPLA2α gene expression. It is likely that nucleolin binding at place of Sp1 on gene promoter could also mediate the regulation of c-Jun/Sp1-activated genes.

The activation of cytosolic phospholipase A 2 ␣ (cPLA 2 ␣) plays an important role in initiating the inflammatory response. The regulation of cPLA 2 ␣ mRNA turnover has been proposed to control cPLA 2 ␣ gene expression under cytokine and growth factor stimulation. However, the detailed mechanism is still unknown. In this report, we have demonstrated that the cPLA 2 ␣ mRNA stability was increased under IL-1␤ treatment in A549 cells. By using EMSAs, HuR was identified as binding with the cPLA 2 ␣ mRNA 3-UTR, and the binding region was located at nucleotides 2716 -2807, a fragment containing AUUUA flanked by U-rich sequences. IL-1␤ treatment enhanced the association of cPLA 2 ␣ mRNA with cytosolic HuR. The reduction of HuR expression by RNA interference technology inhibited IL-1␤-induced cPLA 2 ␣ mRNA and protein expression. Furthermore, blocking the p38 MAPK signaling pathway with SB203580 abolished the effect of IL-1␤-induced cPLA 2 ␣ gene expression. Phosphorylation at residue Thr-118 of HuR is crucial in regulating the interaction between HuR and its target mRNAs. Mutation of HuR Thr-118 reduced the association between HuR and cPLA 2 ␣ mRNA under IL-1␤ treatment. This inhibitory effect was also observed in binding with COX-2 mRNA. This result indicated that p38 MAPK-mediated Thr-118 phosphorylation may play a key role in regulating the interaction of HuR with its target mRNAs in inflammation.2 is a key enzyme that catalyzes the hydrolysis of membrane glycerophospholipids at the sn-2 position to form arachidonic acid and lysophospholipids (1). These bioactive lipids initiate the production of eicosanoids, which play important roles in inflammation, cancer, and other cellular processes. Therefore, cPLA 2 ␣ has been implicated in the pathogenesis of multiple diseases (2). For example, the up-regulation of cPLA 2 ␣ activity and arachidonic acid release in spinal cord tissue was observed within hours after neurotrauma. Treatment with the cPLA 2 ␣ inhibitor arachidonyl-trifluoromethyl ketone (AACOCF 3 ) increases the survival of neurons and oligodendrocytes in rats that received compression spinal cord injuries (3). Moreover, it has been shown that reduced cPLA 2 ␣ expression contributes to a remarkable resistance to acute respiratory distress syndrome (ARDS), asthma, and collagen-induced arthritis in the cPLA 2 ␣-deficient mouse model (4 -6). In addition, dysregulation of cPLA 2 ␣ has been documented in carcinogenesis. Depletion of cPLA 2 ␣ in bone marrow-derived macrophages prevents spontaneous lung metastasis from primary tumors (7). Mice that carry APC Min/ϩ , a germ line mutation in the adenomatous polyposis coli gene, and cPLA 2 ␣ Ϫ/Ϫ , which lacks cPLA 2 ␣ expression, have an 83% reduction in intestinal tumorigenesis compared with wild type mice (8).The expression levels of cPLA 2 ␣ are tightly regulated to maintain the optimum balance of eicosanoid metabolites (9). Proinflammatory cytokines and growth factors have been demonstrated to activate the cPLA 2 ␣ expression, and the transcriptional regulation mechan...