Prdx6 (peroxiredoxin 6), a bifunctional protein with both GSH peroxidase and PLA2 (phospholipase A2) [aiPLA2 (acidic calcium-independent PLA2)] activities, is responsible for the metabolism of lung surfactant phospholipids. We propose that the aiPLA2 activity of the enzyme is regulated through phosphorylation. Incubation of isolated rat alveolar type II cells (AECII) with PMA, a PKC (protein kinase C) agonist, had no effect on Prdx6 expression but led to ∼75% increase in aiPLA2 activity that was abolished by pretreatment of cells with the MAPK (mitogen-activated protein kinase) inhibitors, SB202190 or PD98059. Prdx6 phosphorylation after incubation of AECII with PMA was demonstrated by autoradiography after immunoprecipitation with either anti-phosphothreonine o-phosphoserine antibodies. in vitro, several active isoforms of ERK (extracellular-signal-regulated kinase) and p38 phosphorylated Prdx6, resulting in an 11-fold increase in aiPLA2 activity. The increased activity was calcium-independent and was abolished by the aiPLA2 inhibitors, surfactant protein A and hexadecyl-3-trifluorethylglycero-sn-2-phospho-methanol (MJ33). The peroxidase activity of Prdx6 was unaffected by phosphorylation. Mass spectroscopic analysis of in vitro phosphorylated Prdx6 showed a unique phosphorylation site at Thr-177 and mutation of this residue abolished protein phosphorylation and the increase in MAPK-mediated activity. These results show that the MAPKs can mediate phosphorylation of Prdx6 at Thr-177 with a consequent marked increase in its aiPLA2 activity.
Pharmacophore generation, atom-based 3D-QSAR, docking, and virtual screening studies of p38-α mitogen activated protein kinase inhibitors: pyridopyridazin-6-ones (part 2)
