MAPK kinase kinase-1 is essential for cytokine-induced c-Jun NH2-terminal kinase and nuclear factor-kappaB activation in human pancreatic islet cells.
OBJECTIVE
The transcription factor nuclear factor-kappaB (NF-kappaB) and the mitogen-activated protein kinases (MAPKs) c-Jun NH(2)-terminal kinase (JNK) 1/2 are known to play decisive roles in cytokine-induced damage of rodent beta-cells. The upstream events by which these factors are activated in response to cytokines are, however, uncharacterized. The aim of the present investigation was to elucidate a putative role of the MAPK kinase kinase-1 (MEKK-1) in cytokine-induced signaling.


METHODS
To establish a functional role of MEKK-1, the effects of transient MEKK-1 overexpression in betaTC-6 cells, achieved by lipofection and cell sorting, and MEKK-1 downregulation in betaTC-6 cells and human islet cells, achieved by diced-small interfering RNA treatment, were studied.


RESULTS
We observed that overexpression of wild-type MEKK-1, but not of a kinase dead MEKK-1 mutant, resulted in potentiation of cytokine-induced JNK activation, inhibitor of kappaB (IkappaB) degradation, and cell death. Downregulation of MEKK-1 in human islet cells provoked opposite effects, i.e., attenuation of cytokine-induced JNK and MKK4 activation, IkappaB stability, and a less pronounced NF-kappaB translocation. betaTC-6 cells with a downregulated MEKK-1 expression displayed also a weaker cytokine-induced iNOS expression and lower cell death rates. Also primary mouse islet cells with downregulated MEKK-1 expression were protected against cytokine-induced cell death.


CONCLUSIONS
MEKK-1 mediates cytokine-induced JNK- and NF-kappaB activation, and this event is necessary for iNOS expression and cell death.
Mokhtari
Dariush
D
Department of Medical Cell Biology, Uppsala University, Uppsala, Sweden.
Myers
Jason W
JW
Welsh
Nils
N
D000818:Animals; D016923:Cell Death; D016207:Cytokines / Q000494:pharmacology*; D018076:DNA, Complementary / Q000235:genetics; D004790:Enzyme Induction; D017930:Genes, Reporter; D006801:Humans; D007515:Islets of Langerhans / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D048728:MAP Kinase Kinase Kinase 1 / Q000378:metabolism*; D051379:Mice; D048055:Mitogen-Activated Protein Kinase 8 / Q000235:genetics / Q000378:metabolism; D016328:NF-kappa B / Q000502:physiology*; D052247:Nitric Oxide Synthase Type II / Q000096:biosynthesis; D010766:Phosphorylation; D034741:RNA, Small Interfering / Q000235:genetics
D016207:Cytokines; D018076:DNA, Complementary; D016328:NF-kappa B; D034741:RNA, Small Interfering; D052247:Nitric Oxide Synthase Type II; D048055:Mitogen-Activated Protein Kinase 8; D048728:MAP Kinase Kinase Kinase 1; C482576:MAP3K1 protein, human