Inhibition of MafA transcriptional activity and human insulin gene transcription by interleukin-1beta and mitogen-activated protein kinase kinase kinase in pancreatic islet beta cells.
OBJECTIVE
Inappropriate insulin secretion and biosynthesis are hallmarks of beta cell dysfunction and contribute to the progression from a prediabetic state to overt diabetes mellitus. During the prediabetic state, beta cells are exposed to elevated levels of proinflammatory cytokines. In the present study the effect of these cytokines and mitogen-activated protein kinase kinase kinase 1 (MEKK1), which is known to be activated by these cytokines, on human insulin gene (INS) transcription was investigated.


METHODS
Biochemical methods and reporter gene assays were used in a beta cell line and in primary pancreatic islets from transgenic mice.


RESULTS
IL-1beta and MEKK1 specifically inhibited basal and membrane depolarisation and cAMP-induced INS transcription in the beta cell line. Also, in primary islets of reporter gene mice, IL-1beta reduced glucose-stimulated INS transcription. A 5'- and 3'-deletion and internal mutation analysis revealed the rat insulin promoter element 3b (RIPE3b) to be a decisive MEKK1-responsive element of the INS. RIPE3b conferred strong transcriptional activity to a heterologous promoter, and this activity was markedly inhibited by MEKK1 and IL-1beta. RIPE3b is also known to recruit the transcription factor MafA. We found here that MafA transcription activity is markedly inhibited by MEKK1 and IL-1beta.


CONCLUSIONS
These data suggest that IL-1beta through MEKK1 inhibits INS transcription and does so, at least in part, by decreasing MafA transcriptional activity at the RIPE3b control element. Since inappropriate insulin biosynthesis contributes to beta cell dysfunction, inhibition of MEKK1 might decelerate or prevent progression from a prediabetic state to diabetes mellitus.
Oetjen
E
E
Department of Molecular Pharmacology, University of Göttingen, Robert-Koch-Strasse 40, 37099 Göttingen, Germany. eoetjen@med.uni-goettingen.de
Blume
R
R
Cierny
I
I
Schlag
C
C
Kutschenko
A
A
Krätzner
R
R
Stein
R
R
Knepel
W
W
D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D045744:Cell Line, Tumor; D006801:Humans; D007328:Insulin / Q000235:genetics*; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D007371:Interferon-gamma / Q000494:pharmacology; D053583:Interleukin-1beta / Q000494:pharmacology*; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D020930:MAP Kinase Kinase Kinases / Q000235:genetics / Q000378:metabolism*; D050977:Maf Transcription Factors / Q000235:genetics*; D051379:Mice; D008822:Mice, Transgenic; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D020218:Response Elements / Q000235:genetics; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D007328:Insulin; D053583:Interleukin-1beta; D050977:Maf Transcription Factors; D011993:Recombinant Fusion Proteins; D014409:Tumor Necrosis Factor-alpha; D007371:Interferon-gamma; D008156:Luciferases; D020930:MAP Kinase Kinase Kinases