Regulation of KV11.1 C-Terminal Isoform Expression by HU Proteins

Abstract

The KCNH2 gene encodes the Kv11.1 potassium channel that conducts the rapidly activating delayed rectifier current in the heart. KCNH2 pre-mRNA undergoes alternative processing; intron 9 splicing leads to the formation of a functional, full-length Kv11.1a isoform, while polyadenylation within intron 9 generates a non-functional, C-terminally truncated Kv11.1a-USO isoform. The relative expression of Kv11.1 isoforms is regulated in a development and tissue-specific manner. The molecular mechanisms that regulate Kv11.1 isoform expression are poorly understood. In this study, we identified the RNA binding proteins HuR and HuD as regulators of Kv11.1 isoform expression. In co-transfection experiments we showed that HuR and HuD increased Kv11.1a isoform expression and decreased Kv11.1a-USO isoform expression by Western blot analysis and by the RNase protection assay. In patch-clamp experiments, we found that HuR and HuD significantly increased Kv11.1 current. siRNA-mediated knockdown of HuR protein nearly abolished expression of the Kv11.1a isoform and increased the expression level of the Kv11.1a-USO isoform. Our findings suggest that the relative expression of Kv11.1 C-terminal isoforms can be regulated by HuR and HuD proteins.