Signal transduction of pregnenolone sulfate in insulinoma cells: activation of Egr-1 expression involving TRPM3, voltage-gated calcium channels, ERK, and ternary complex factors.
The neurosteroid pregnenolone sulfate acts on the nervous system by modifying neurotransmission and receptor functions, thus influencing synaptic strength, neuronal survival, and neurogenesis. Here we show that pregnenolone sulfate induces a signaling cascade in insulinoma cells leading to enhanced expression of the zinc finger transcription factor Egr-1 and Egr-1-responsive target genes. Pharmacological and genetic experiments revealed that influx of Ca(2+) ions via transient receptor potential M3 and voltage-gated Ca(2+) channels, elevation of the cytosolic Ca(2+) level, and activation of ERK are essential for connecting pregnenolone sulfate stimulation with enhanced Egr-1 biosynthesis. Expression of a dominant-negative mutant of Elk-1, a key regulator of gene transcription driven by a serum response element, attenuated Egr-1 expression following stimulation, indicating that Elk-1 or related ternary complex factors connect the transcription of the Egr-1 gene with the pregnenolone sulfate-induced intracellular signaling cascade elicited by the initial influx of Ca(2+). The newly synthesized Egr-1 was biologically active and bound under physiological conditions to the regulatory regions of the Pdx-1, Synapsin I, and Chromogranin B genes. Pdx-1 is a major regulator of insulin gene transcription. Accordingly, elevated insulin promoter activity and increased mRNA levels of insulin could be detected in pregnenolone sulfate-stimulated insulinoma cells. Likewise, the biosynthesis of synapsin I, a synaptic vesicle protein that is found at secretory granules in insulinoma cells, was stimulated in pregnenolone sulfate-treated INS-1 cells. Together, these data show that pregnenolone sulfate induces a signaling cascade in insulinoma cells that is very similar to the signaling cascade induced by glucose in β-cells.
Department of Medical Biochemistry and Molecular Biology, University of Saarland Medical Center, D-66421 Homburg, Germany.
Sabine I
SI
Mayer
Isabelle
I
Müller
Stefanie
S
Mannebach
Takeshi
T
Endo
Gerald
G
Thiel
D000818:Animals; D002118:Calcium / Q000378:metabolism; D045744:Cell Line, Tumor; D051766:Early Growth Response Protein 1 / Q000096:biosynthesis* / Q000235:genetics; D004789:Enzyme Activation / Q000187:drug effects / Q000235:genetics; D048049:Extracellular Signal-Regulated MAP Kinases / Q000235:genetics / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects* / Q000235:genetics; D007340:Insulinoma / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000096:biosynthesis* / Q000235:genetics; D011284:Pregnenolone / Q000494:pharmacology*; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects* / Q000235:genetics; D050053:TRPM Cation Channels / Q000235:genetics / Q000378:metabolism*
D051766:Early Growth Response Protein 1; C486109:Egr1 protein, mouse; C486110:Egr1 protein, rat; D046912:Multiprotein Complexes; D009363:Neoplasm Proteins; D050053:TRPM Cation Channels; C533868:TRPM3 protein, mouse; C533867:TRPM3 protein, rat; D011284:Pregnenolone; D048049:Extracellular Signal-Regulated MAP Kinases; D002118:Calcium
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