Identification and characterization of a neuroendocrine-specific 5'- regulatory region of the human chromogranin A gene

Abstract

Chromogranin A (CgA) expression is specific to cells of endocrine and neuroendocrine (NE) tissues. Our transfection studies with CgA have identified two DNA regions 5' of the transcription start site that regulate CgA gene transcription: a distal regulatory region (DRR) located between -726 and -455, and a proximal regulatory region (PRR) between -60 and -26. In studies of the DRR using four human NE and six human non-NE cell lines, we demonstrated enhanced transcription of DRR-containing CgA-GH plasmids by the NE cells as a group compared to the non-NE cells. DNase I footprinting identified a protected area in the DRR from -570 to -555 base pairs (bp) composed of the sequence TAATGATGACTAAACA. Centered in this sequence is the simian virus 40 version of the activator protein-1-binding site, TGACTAA. Electrophoretic mobility shift assays (EMSAs) with an oligonucleotide containing the 27 bp of the DRR between -576 and -550, which we refer to as the distal regulatory element (DRE), produced a specific complex with the NE BEN and non-NE COS-1 cell nuclear extracts. The addition of c-Jun and c-Fos antibodies produced strong supershifts of the complex generated by COS-1 extract, but very weak supershifts of the complex formed by BEN extract. These EMSA studies suggest that NE cells such as BEN contain unique nuclear factors distinguishable from activator protein-1 that interact with the DRE. The enhancer effect of the 271-bp DRR could be replaced by the 27-bp DRE in both CgA and calcitonin promoter constructs in BEN cells. Replacement of the DRR with the DRE resulted in a further increase in expression from these plasmids, suggesting the presence of suppressor sequences in the DRR. In transfection studies of the PRR, deletion of its cAMP response element (CRE) dramatically lowered transcription. In addition to demonstrating that its CRE can bind CRE-binding protein, EMSAs with the PRR demonstrated that an intervening sequence between the CRE and the TATA box formed a complex with BEN cell nuclear extract. Our studies demonstrate that both the PRR and DRR are important for high level transcription of the CgA gene in NE cells. The presence of both distal and proximal 5'-regulatory regions in the human CgA gene indicates a complex mechanism of transcriptional regulation. Although the PRR is important for the formation of a functional transcription complex at the TATA region, the DRR is important for the enhancement of CgA gene expression in NE cells.