Osmotic regulation of MG-132-induced MAP-kinase phosphatase MKP-1 expression in H4IIE rat hepatoma cells.
OBJECTIVE
Proteasome inhibitors such as MG-132 are considered as potential therapeutical tools in different clinical settings. The dual specificity MAP-kinase phosphatase MKP-1 plays a role in balancing signals mediating cell death or survival. Here the effect of cell hydration on MG-132-induced MKP-1 expression was investigated in H4IIE rat hepatoma cells.


RESULTS
Hyperosmolarity (405mosmol/l) increased MKP-1 expression by MG-132, which was accompanied by an induction of c-Fos, c-Jun, cJun Ser73 phosphorylation, and AP-1 DNA binding. MKP-1 induction by MG-132 plus hyperosmolarity was sensitive to inhibition of p38(MAPK) and c-Jun-N-terminal kinases (JNKs) but not extracellular signal-regulated kinases Erk-1/Erk-2, and was accompanied by a decline of MAP-kinase activities. Although hyperosmolarity increased overall protein ubiquitination in presence of MG-132, ubiquitination of MKP-1 was found under normo-, but not hyperosmotic conditions. Hyperosmolarity also enabled MG-132 to induce poly-ADP-ribose polymerase (PARP) cleavage which was sensitive to inhibition of p38(MAPK) and JNKs but not Erk-1/Erk-2. PARP cleavage and caspase-3 activation in H4IIE cells treated with hyperosmolarity plus MG-132 was further increased by vanadate, consistent with a contribution of MKP-1 to counterbalance proapoptotic MAP-kinase signals.


CONCLUSIONS
The findings suggest that among other factors cell hydration critically determines the cellular response to proteasome inhibitors.
Lornejad-Schafer
Mohammad
M
Institute of Environmental Medical Research, Molecular Ageing Research Dusseldorf, Germany.
Schafer
Christine
C
Richter
Lisa
L
Grune
Tilman
T
Haussinger
Dieter
D
Schliess
Freimut
F
D000818:Animals; D018797:Cell Cycle Proteins / Q000235:genetics* / Q000378:metabolism; D045744:Cell Line, Tumor; D048429:Cell Size / Q000187:drug effects; D054638:Dual Specificity Phosphatase 1; D005786:Gene Expression Regulation; D017874:Immediate-Early Proteins / Q000235:genetics* / Q000378:metabolism; D007976:Leupeptins / Q000494:pharmacology*; D008114:Liver Neoplasms, Experimental; D010749:Phosphoprotein Phosphatases / Q000235:genetics* / Q000378:metabolism; D011480:Protease Inhibitors / Q000494:pharmacology*; D061988:Proteasome Inhibitors; D054645:Protein Phosphatase 1; D017027:Protein Tyrosine Phosphatases / Q000235:genetics* / Q000378:metabolism; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D051381:Rats; D012462:Saline Solution, Hypertonic
D018797:Cell Cycle Proteins; D017874:Immediate-Early Proteins; D007976:Leupeptins; D011480:Protease Inhibitors; D061988:Proteasome Inhibitors; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D012462:Saline Solution, Hypertonic; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D054638:Dual Specificity Phosphatase 1; C517021:Dusp1 protein, rat; D017027:Protein Tyrosine Phosphatases; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde