© 2000 by European Society of Cardiology
Copyright © 2000, European Society of Cardiology
Hypoxia differentially regulates stress proteins in cultured cardiomyocytes
Role of the p38 stress-activated kinase signaling cascade, and relation to cytoprotection
Cardiology Section, VA Medical Center, 4150 Clement Street, San Francisco, CA 94121, USA
* Corresponding author. Tel.: +1-415-750-2112; fax: +1-415-750-6950 joel.karliner{at}med.va.gov
Objective: Stress proteins (heat shock proteins, HSPs) are molecular chaperones that have been shown to enhance the survival of cells exposed to environmental stress. We sought to investigate the effects of hypoxia on the levels of HSP27 and heme oxygenase-1 (HO-1 or HSP32) in an established model of rat neonatal cardiac myocytes in culture. Methods: Myocytes were subjected to hypoxia (<0.5% O2 for 16 h). Studies of cell viability and nuclear morphology showed no evidence of cell death under these conditions. Results: Messenger RNA analysis demonstrated constitutive expression of HSP27 and low levels of HO-1. Hypoxia strongly induced HO-1 mRNA without affecting HSP27 mRNA. In parallel to mRNA levels, hypoxia increased HO-1 protein level without affecting HSP27. To further assess the signaling pathways implicated in HO-1 induction, we used inhibition experiments. The tyrosine kinase inhibitor tyrphostin and the mitogen-activated protein kinase inhibitor PD98059 did not prevent HO-1 induction, while the protein kinase C inhibitor chelerythrine partially blocked this response. The p38 stress-activated kinase inhibitor SB203580 was the most potent in suppressing hypoxia-induced HO-1. In vitro kinase assays, cell labeling and immunoprecipitation showed activation of signaling pathways downstream of p38 stress-activated kinase as revealed by an increase in phosphorylation of MAPKAPK-2/3 kinases and HSP27. Conclusions: These data show a differential pattern of hypoxia-induced HSP expression and implicate the stress kinase in HO-1 induction. Thus, selective regulation of HSP levels may play a role in the cardioprotective mechanisms that participate in the adaptive response to hypoxia-induced stress.
KEYWORDS HSPs: stress proteins or heat shock proteins; HO-1: Heme oxygenase-1 or a 32-kDa heat shock protein (HSP32); PMA: phorbol 12-myristate 13-acetate; PKC: protein kinase C; IL-1β: interleukin-1β; MTT: Tetrazolium dye 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium; RT-PCR: reverse transcriptase polymerase chain reaction; ERK: extracellular signal-regulated protein kinase; MAP kinase: mitogen-activated protein kinase; p38/RK: a MAP kinase called stress-activated protein kinase (SAPK) or reactive kinase (RK); MAPKAPK-2/3: MAP kinase kinase-2/3; PI: propidium iodide; PBS/T: phosphate buffered saline–Tween 0.05; PD98059: MEK-1 inhibitor; SB203580: p38/RK stress kinase inhibitor; BCA: Bicinchoninic acid reagent
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