Activation and role of MAP kinase-dependent pathways in retinal pigment epithelium cells: JNK1, P38 kinase, and cell death.
OBJECTIVE
Retinal pigment epithelial (RPE) cell death is an important step in the pathogenesis of ocular diseases. JNK1 and P38 kinase, two stress-activated kinases, play key roles relaying stress signals leading to cell death through cyclin D1 and c-Myc. Recently, stress-activated kinases have been shown to regulate cell proliferation. In the current study, the involvement of the JNK1 and P38 kinase signaling pathways in RPE cell proliferation and death was investigated.


METHODS
RPE cell proliferation was stimulated with 10% fetal calf serum (FCS). Activation of the JNK1 and P38 kinase cascades and their potential targets was detected by Western blot analysis. Pharmacologic inhibitors and activators, and antisense oligodeoxynucleotides (ODN) directed against the stress kinases were used to analyze the signaling involved in RPE cell death.


RESULTS
P38 and JNK1 and their respective upstream activating kinases, MKK3/6 and -4, were all transiently activated in FCS-stimulated RPE cell cultures. Ras controlled only the activation of JNK1, whereas Rho transmitted the activation of both JNK1 and P38, suggesting parallel signaling pathways and cross talk between the two kinases. Pharmacologic inhibition of JNK1 did not affect cell proliferation in FCS-stimulated cells. Inactivation of P38 kinase and antisense ODN-induced downregulation of P38 kinase also had no affect on cell proliferation. Long-term, high-level activation of JNK1 and P38 kinase occurred during serum depletion-induced RPE cell death. Overactivation of JNK1 and P38 kinase was also observed during pharmacologically induced cell death, suggesting that this process is common to RPE cell-death-signaling pathways induced by various stress stimuli. Cell death mediated by the overactivation of JNK1 and P38 kinase was cyclin D1- and c-Myc-independent.


CONCLUSIONS
The inhibition of JNK1 or P38 kinase had no effect on FCS-stimulated proliferation of RPE cells, whereas the overactivation of these two enzymes was involved in RPE cell death in FCS-depleted cultures. Parallel upstream signaling pathways and cross talk between the two kinases suggest that the regulation of signaling in RPE cell death is complex.
Hecquet
Christiane
C
Cordeliers Biomedical Institute, National Institute of Health and Medical Research, Unit 450, National Center for Scientific Research, Paris, France.
Lefevre
Gaëlle
G
Valtink
Monika
M
Engelmann
Katrin
K
Mascarelli
Frederic
F
D017209:Apoptosis; D015153:Blotting, Western; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002455:Cell Division; D002478:Cells, Cultured; D015536:Down-Regulation; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D048371:MAP Kinase Kinase 3; D048670:MAP Kinase Kinase 4; D048669:MAP Kinase Kinase 6; D020935:MAP Kinase Signaling System / Q000502:physiology*; D048055:Mitogen-Activated Protein Kinase 8; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010857:Pigment Epithelium of Eye / Q000201:enzymology / Q000473:pathology*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases
D004791:Enzyme Inhibitors; D011505:Protein-Tyrosine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048055:Mitogen-Activated Protein Kinase 8; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048371:MAP Kinase Kinase 3; D048670:MAP Kinase Kinase 4; D048669:MAP Kinase Kinase 6; C482530:MAP2K3 protein, human; C482559:MAP2K4 protein, human; C482566:MAP2K6 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases