Involvement of p38 mitogen-activated protein kinase signaling pathway in the rapid induction of the 78-kDa glucose-regulated protein in 9L rat brain tumor cells.
We have previously shown that treatment with okadaic acid (OA) followed by heat shock (HS) (termed OA --> HS treatment) leads to rapid transactivation of the 78-kDa glucose-regulated protein gene (grp78) in 9L rat brain tumor cells. A cAMP-responsive element-like (CRE-like, TGACGTGA) promoter sequence and a protein kinase A signaling pathway are involved in this induction, and activation of both CRE binding protein (CREB) and activating transcription factor-2 (ATF-2) is required in the above process. Herein, we report that transactivation of grp78, as well as phosphorylation/activation of ATF-2, can be completely annihilated by SB203580, a highly specific inhibitor of p38 mitogen-activated protein kinase (p38(MAPK)). Activation of p38(MAPK) by OA --> HS is also substantiated by its own phosphorylation as well as the phosphorylation and activation of MAPK activating protein kinase-2 in cells subjected to this treatment. The involvement of p38(MAPK) in the activation of ATF-2, which leads to the transactivation of rat grp78, is confirmed by electrophoretic mobility shift assay using a probe containing the CRE-like sequence as well as by transient transfection assays with a plasmid containing a 710-base pair stretch of the grp78 promoter. Together with our previous studies, these results led us to conclude that phosphorylation/activation of CREB upon OA --> HS treatment is mediated by cAMP-dependent protein kinase, whereas that of ATF-2 is mediated by p38(MAPK). The transcription factors may bind to each other to form heterodimers that in turn transactivate grp78 by binding to the CRE-like element. This suggests that distinct signaling pathways converge on CREB-ATF-2, where each subunit is individually activated by a specific class of protein kinases. This may allow modulation of grp78 transactivation by diverse external stimuli.
Chen
K D
KD
Department of Life Science, National Tsing Hua University, Hsinchu, Taiwan 30043, Republic of China.
Chen
L Y
LY
Huang
H L
HL
Lieu
C H
CH
Chang
Y N
YN
Chang
M D
MD
Lai
Y K
YK
D000818:Animals; D001932:Brain Neoplasms / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000235:genetics; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006360:Heat-Shock Proteins; D007093:Imidazoles / Q000494:pharmacology; D020928:Mitogen-Activated Protein Kinases; D018832:Molecular Chaperones / Q000096:biosynthesis* / Q000235:genetics; D019319:Okadaic Acid / Q000494:pharmacology; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D015398:Signal Transduction; D014158:Transcription, Genetic; D014407:Tumor Cells, Cultured; D048051:p38 Mitogen-Activated Protein Kinases
D002352:Carrier Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; D004791:Enzyme Inhibitors; D006360:Heat-Shock Proteins; D007093:Imidazoles; D018832:Molecular Chaperones; D011725:Pyridines; D019319:Okadaic Acid; D017868:Cyclic AMP-Dependent Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; C093642:SB 203580