Cyclic AMP regulates potassium channel expression in C6 glioma by destabilizing Kv1.1 mRNA

Abstract

The tissue distributions and physiological properties of a variety of cloned voltage-gated potassium channel genes have been characterized extensively, yet relatively little is known about the mechanisms controlling expression of these genes. Here, we report studies on the regulation of Kv1.1 expressed endogenously in the C6 glioma cell line. We demonstrate that elevation of intracellular cAMP leads to the accelerated degradation of Kv1.1 RNA. The cAMP-induced decrease in Kv1.1 RNA is followed by a decrease in Kv1.1 protein and a decrease in the whole cell sustained K ؉ current amplitude. Dendrotoxin-I, a relatively specific blocker of Kv1.1, blocks 96% of the sustained K ؉ current in glioma cells, causing a shift in the resting membrane potential from ؊40 mV to ؊7 mV. These data suggest that expression of Kv1.1 contributes to setting the resting membrane potential in undifferentiated glioma cells. We therefore suggest that receptor-mediated elevation of cAMP reduces outward K ؉ current density by acting at the translational level to destabilize Kv1.1 RNA, an additional mechanism for regulating potassium channel gene expression.Regulation of gene expression can occur at the level of transcription, translation, or posttranslationally. Among the genes encoding voltage-gated potassium (Kv) channels, transcriptional regulation has been analyzed for Kv1.5 and Kv3.1 (1-5). For example, Takimoto et al. (6) demonstrated that expression levels of Kv1.5 were affected at the level of transcription with dexamethasone treatment but that mRNA halflife and protein turnover were unchanged. Posttranslational regulation has also been convincingly demonstrated for a number of Kv channels. For example, phosphorylation by tyrosine kinase, protein kinase C, and protein kinase A have each been shown to modulate Kv channel function (7-9), and a channel-associated ␤-subunit (Kv␤2) has been shown to promote translocation of Kv1.2 to the plasma membrane (10). In contrast, relatively little is known about regulation of Kv genes at the translational level. Given the fact that many Kv transcripts are large (6-12 kb) but contain relatively small ORFs (1.5-2.5 kb), it seems likely that the untranslated portions of these transcripts may have a regulatory function.There exists a variety of forms of translational regulation, including changes in nuclear processing of the transcript (splicing, capping, polyadenylation, and nuclear export) as well as changes in the efficiency of translation (ribosome binding, loading, scanning, and initiation) and changes in transcript stability (reviewed in ref. 11). Well studied examples include S-adenosylmethionine decarboxylase, regulated by changing the efficiency of ribosome loading and scanning (12), and iron metabolism, regulated by blockade of ribosome scanning and by regulation of transcript stability in the ferritin and transferrin receptor genes, respectively (13). Among ion channel genes, Wymore et al. (14) demonstrated that alternatively spliced 3Ј-untranslated regions (UTRs) from Kv1.4 caus...

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“…cAMP increased the transcription rate of a rat cardiac Kv1.5 K ϩ channel gene, but inhibited the transcription of a similar K ϩ channel gene in the rat pituitary GH 3 cell line (Mori et al, 1993). cAMP accelerated the degradation of Kv1.1 K ϩ channel mRNA in a glioma cell line (Allen et al, 1998). The rapid corticotropin and cAMP-induced decrease in AZF cell Kv1.4 K ϩ channel mRNA previously reported also probably occurs through an effect on mRNA stability .…”

A Bovine Adrenocortical Kv1.4 K+ Channel Whose Expression Is Potently Inhibited by ACTH

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