Abstract: Objective To elaluate the involvement of p44/42 kinase(Erk)、AP-1 in the expression of cyclooxygenase-2 (COX-2) in a mouse macula densa derived cell line (MMDD1 cells). Methods MMDD1 cells were transfected with luciferase reporter plasmid containing AP-1. Luciferase reporter assay were studied in normal salt(NS) and low salt(LS) medium; the expression of c-Jun、c-Fos were analyzed as well by Western Blotting. RT-PCR and Western Blotting were used to detect the mRNA and protein expression of COX-2. Expressions of total and phosphorylated Erk were analyzed by Western Blotting in LS solution. The contents of PGE2 in the supernatant were examined by enzyme linked immunosorbent assay (ELISA). Results Phosphorylated Erk were markedly increased by LS treatment. The up-regulated COX-2 protein expression with LS were reduced with PD-98059 (Erk inhibitiors) at 20μM，PGE2 release were down-regulated as well. Luciferase activity of AP-1 were stimulated in LS, the up-regulated luciferase activity of AP-1 were attenuated by curcumin at 20μM (AP-1 inhibitor). The expression of c-Jun、c-Fos were increased as well. Low salt medium altered COX-2 mRNA abundance and protein expression were decreased in treatment with curcumin at 20μM. Conclusions Low salt induces the expression of COX-2 in MMDD1 cells，involves the activation of Erk 、AP-1 pathways.