The p38 mitogen-activated protein kinase pathway is involved in the regulation of heme oxygenase-1 by acidic extracellular pH in aortic smooth muscle cells

Extracellular acidosis (EA) regulates Heme Oxygenase‐1 (HO‐1) expression in vascular smooth muscle cells via transcriptional and posttranscriptional mechanisms but the signaling pathways involved are not known. We examined the role of Mitogen‐Activated Protein Kinase (MAPK) pathways in HO‐1 regulation by EA. Primary rat aortic smooth muscle cells were exposed to EA or physiologic pH. Levels of the total and phosphorylated forms of p38, extracellular signal‐regulated protein kinases1/2 (ERK1/2), c‐Jun N‐terminal kinases/stress‐activated protein kinases (JNK1/2), and HO‐1 protein were assessed by Western analysis and HO‐1 mRNA levels were assessed by quantitative PCR. Inhibition of p38 MAPK was achieved with the chemical inhibitor SB203580, or adenoviral infection of a dominant‐negative form of p38α. Phospho p38 MAPK activity was evaluated with an in vitro kinase activity assay. Binding of Activator Protein‐1 (AP‐1), a known target of MAPK pathways, was assessed by Electromobility shift assay (EMSA). EA induced phosphorylation of p38 MAPK in a biphasic manner while total p38 was unchanged. EA did not alter levels of phospho ERK 1/2 and phospho JNK 1/2. There was increased phospho p38 MAPK activity in the setting of EA which preceded the induction of HO‐1. Inhibition of phospho p38 activity with either SB20358 or a dominant negative p38α oligonucleotide abrogated the induction of HO‐1 by EA. Increased specific binding of AP‐1 in the setting of EA was shown by EMSA. Increased phospho p38 activity precedes and likely mediates HO‐1 induction by EA. Increased AP‐1 binding may underlie the transcriptional regulation of HO‐1 by EA. J. Cell. Biochem. 105: 1298–1306, 2008. © 2008 Wiley‐Liss, Inc.