ABSTRACT
<p><b>OBJECTIVE</b>To evaluate the effect of low salt (LS) on the expression of cyclooxygenase-2 (COX-2) and the activity of nuclear factor kappa B (NF-kappaB) and activator protein-1 (AP-1) in the mouse macula densa derived (MMDD1) cell line.</p><p><b>METHODS</b>MMDD1 cells were transfected with luciferase reporter plasmid containing AP-1 or NF-kappaB. Luciferase reporter assay was used to evaluate the effect of normal salt (NS) and low salt (LS) on the activities of NF-kappaB and AP-1. The changes of COX-2 expression were examined by RT-PCR. The expression of p-p38 MAPK, p-p44/42, c-Jun, c-Fos, and COX-2 in MMDD1 cells were analyzed by Western blot.</p><p><b>RESULTS</b>The expressions of COX-2 mRNA and protein in MMDD1 cells were significantly increased by LS (P < 0.01). Phosphorylated p38 and p44/42 MAP kinase were significantly increased by treatment at 180 min (P < 0.01). The up-regulated COX-2 protein expression with LS were significantly reduced with SB 203580 (p38 inhibitors) and PD-98059 (p44/42 inhibitors) (P < 0.01). The expressions of c-Jun and c-Fos were increased by LS. The luciferase activities of AP-1 and NF-kappaB were stimulated in LS (P < 0.01), the up-regulated luciferase activities were attenuated by PDTC at 25 micromol/L (NF-kappaB inhibitor) and curcumin at 20 micromol/L (AP-1 inhibitor) (P < 0.01). LS altered COX-2 mRNA abundance and protein expression were decreased in treatment with PDTC at 25 micromol/L, curcumin at 20 micromol/L (P < 0.01).</p><p><b>CONCLUSION</b>LS can induce the expression of COX-2 in MMDD1 cells, which may be involved in the activation of p38 MAP kinase, p44/42 kinase, AP-1, and NF-kappaB pathways.</p>