Atrial natriuretic peptide attenuates ANG II-induced hypertrophy of renal tubular cells

ANG II arrests LLC-PK(1) cells in the G(1) phase of the cell cycle and induces hypertrophy, an effect mediated by induction of p27(Kip1). We studied whether atrial natriuretic peptide (ANP) may modulate ANG II-induced hypertrophy and p27(Kip1) expression in tubular LLC-PK(1) cells. ANP, through its fragments 3-28 and 4-27, prevented ANG II-induced cell cycle arrest. ANP inhibited >80% of ANG II-induced p27(Kip1) protein expression (Western blots). ANP stimulated expression of MKP-1, a phosphatase involved in dephosphorylation of p44/42 mitogen-activated protein (MAP) kinase, up to 12 h. ANP prevented the ANG II-mediated phosphorylation peak of MAP kinase after 12 h of stimulation. 8-Bromo-cGMP mimicked all the effects of ANP. Transfection with MKP-1 antisense, but not sense, oligonucleotides abolished the modifying role of ANP on ANG II-mediated cell cycle arrest. The effect of ANP on ANG II-mediated hypertrophy of LLC-PK(1) cells is regulated on the level of MAP kinase phosphorylation, a key step in the induction of p27(Kip1). Although ANP and ANG II both stimulate generation of reactive oxygen species, ANP additionally induces expression of MKP-1, leading to interference with ANG II-mediated MAP kinase phosphorylation.