Truncated K+ channel DNA sequences specifically suppress lymphocyte K+ channel gene expression.

We have constructed a series of deletion mutants of Kv1.3, a Shaker-like, voltage-gated K+ channel, and examined the ability of these truncated mutants to form channels and to specifically suppress full-length Kv1.3 currents. These constructs were expressed heterologously in both Xenopus oocytes and a mouse cytotoxic T cell line. Our results show that a truncated mutant Kv1.3 must contain both the amino terminus and the first transmembrane-spanning segment, S1, to suppress full-length Kv1.3 currents. Amino-terminal-truncated DNA sequences from one subfamily suppress K+ channel expression of members of only the same subfamily. The first 141 amino acids of the amino-terminal of Kv1.3 are not necessary for channel formation. Deletion of these amino acids yields a current identical to that of full-length Kv1.3, except that it cannot be suppressed by a truncated Kv1.3 containing the amino terminus and S1. To test the ability of truncated Kv1.3 to suppress endogenous K+ currents, we constructed a plasmid that contained both truncated Kv1.3 and a selection marker gene (mouse CD4). Although constitutively expressed K+ currents in Jurkat (a human T cell leukemia line) and GH3 (an anterior pituitary cell line) cells cannot be suppressed by this double-gene plasmid, stimulated (up-regulated) Shaker-like K+ currents in GH3 cells can be suppressed.