A Promoter in the Coding Region of the Calcium Channel Gene CACNA1C Generates the Transcription Factor CCAT

The C-terminus of the voltage-gated calcium channel Ca(v)1.2 encodes a transcription factor, the calcium channel associated transcriptional regulator (CCAT), that regulates neurite extension and inhibits Ca(v)1.2 expression. The mechanisms by which CCAT is generated in neurons and myocytes are poorly understood. Here we show that CCAT is produced by activation of a cryptic promoter in exon 46 of CACNA1C, the gene that encodes Ca(V)1.2. Expression of CCAT is independent of Ca(v)1.2 expression in neuroblastoma cells, in mice, and in human neurons derived from induced pluripotent stem cells (iPSCs), providing strong evidence that CCAT is not generated by cleavage of Ca(V)1.2. Analysis of the transcriptional start sites in CACNA1C and immune-blotting for channel proteins indicate that multiple proteins are generated from the 3' end of the CACNA1C gene. This study provides new insights into the regulation of CACNA1C, and provides an example of how exonic promoters contribute to the complexity of mammalian genomes.