Destabilization of Nav1.7 sodium channel α-subunit mRNA by constitutive phosphorylation of extracellular signal-regulated kinase:: Negative regulation of steady-state level of cell surface functional sodium channels in adrenal chromaffin cells

In cultured bovine adrenal chromaffin cells expressing Na(v)1.7 isoform of voltage-dependent Na+ channels, treatment (greater than or equal to6 h) with serum deprivation, PD98059, or U0126 increased cell surface [H-3]saxitoxin ([H-3]STX) binding by similar to58% (t(1/2) = 12.5 h), with no change in the K-d value. Immunoblot analysis showed that either treatment attenuated constitutive phosphorylation of extracellular signal-regulated kinase (ERK) 1 and ERK2 but not of p38 mitogen-activated protein kinase and c-Jun N-terminal kinase (JNK) 1 and JNK2. The increase of [H-3]STX binding and the attenuated phosphorylation of ERK1 and ERK2 returned to the control nontreated levels after the addition of serum or the washout of PD98059- or U0126-treated cells. Simultaneous treatment of serum deprivation with PD98059 or U0126 did not produce an additional increasing effect on [H-3]STX binding, compared with either treatment alone. In cells subjected to either treatment, veratridine-induced maximum Na-22(+) influx was augmented by similar to47%, with no change in the EC50 value; Ptychodiscus brevis toxin-3 enhanced veratridine-induced Na-22(+) influx by 2-fold, as in nontreated cells. Serum deprivation, PD98059, or U0126 increased Na+ channel alpha- but not beta(1)-subunit mRNA level by similar to50% between 3 and 24 h; cycloheximide, an inhibitor of protein synthesis, increased alpha-subunit mRNA level and nullified additional increasing effect of either treatment on alpha-subunit mRNA level. Either treatment prolonged half-life of alpha-subunit mRNA from 17.5 to similar to26.3 h without altering alpha-subunit gene transcription. Thus, constitutively phosphorylated/activated ERK destabilizes Na+ channel alpha-subunit mRNA via translational event, which negatively regulates steady-state level of alpha-subunit mRNA and cell surface expression of functional Na+ channels.