Genomic organization and promoter analysis of human KCNN3 gene

KCNN3 is a member of the gene family, KCNN1-4, encoding the small and intermediate conductance calcium-activated potassium channels. Long CAG-repeat alleles of this gene have been found to be over-represented in patients with schizophrenia in a number of population-based association studies, and this gene maps to human chromosome 1q21, a region recently implicated in schizophrenia by linkage. To set the stage for a further functional evaluation of KCNN3, we defined the nature of the genomic locus in the size, structure, and sequence of its introns and exons and the function of potential upstream regulatory regions. We isolated P1-derived artificial chromosome (PAC) clones from a genomic library and identified an overlapping available bacterial artificial chromosome (BAC) clone. Cosmids subcloned from the PAC and BAC clones were then sequenced and merged with the sequence in the public database. The KCNN3 gene spans over 163.1 kb and is composed of eight exons and seven introns. All of the exon-intron junctions conform closely to consensus splice sites. The proximal 2.5 kb of the 5'-flanking sequence was obtained and analyzed for potential transcription factor binding sites. In the proximal 2.5 kb upstream region, potential sites for the Ikaros factor (IK2), homeodomain factor Nkx-2.5/Csx (NKX25), nuclear factor of activated T-cells (NFAT), upstream stimulating factor (USF), c-AMP responsive element binding protein (CREB), POU factor Brn2 (BRN-2), myeloid zinc finger protein (MZF1), vitellogenin binding protein (VBP), HNF3 forkhead homologue 2 (HFH2), and transcription initiation were identified, as well as several potential AP-1 and AP-4 sites. Finally, a 2261-bp fragment of this upstream region was cloned into a promoterless pGL3-luciferase vector, where it produced orientation-dependent expression of the reporter gene in transiently transfected PC12 cells, cells which natively express functional KCNN3 channels, suggesting that this cloned fragment includes competent promoter elements of this gene.