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.