Identification of the Promoter Region and the 5′-Untranslated Exons of the Human Voltage-Gated Sodium Channel Nav1.1 Gene (SCN1A) and Enhancement of Gene Expression by the 5′-Untranslated Exons

Voltage-gated sodium channels play critical roles in the excitability of the brain. A decreased level of Na(v)1.1 has been identified as the cause of severe myoclonic epilepsy in infancy. In the present study, we identified the transcription start site and three 5'-untranslated exons of SCN1A by using 5'-full RACE. The 2.5-kb region upstream of the transcription start site was targeted as a potential location of the promoter. The 2.5-kb genomic fragment (P-2.5, from +26 to -2,500) and the 2.7-kb fragment (P-2.7, P-2.5 combined with the 227-bp 5'-untranslated exons) were cloned to produce luciferase constructs. The P-2.5 and the P-2.7 drove luciferase gene expression in the human neuroblastoma cell line SH-SY5Y but not in the human embryonic kidney cell line HEK-293. The 5'-untranslated exons could greatly enhance gene expression in SH-SY5Y cells. The P-2.7 could be used as a functional unit to study the role of SCN1A noncoding sequences in gene expression. These findings will also help in exploring the possibility of promoter mutant-induced diseases and revealing the mechanism underlying the regulation of SCN1A expression in the normal brain. (C) 2008 Wiley-Liss, Inc.