The upstream region of the mouse N- myc gene: Identification of an enhancer element that functions preferentially in neuroblastoma IMR32 cells

Abstract

The various members of the myc gene family, including c- myc and N- myc, are supposed to play a role in the regulation of cell cycle and proliferation. Whereas c- myc is expressed nearly ubiquitously, the N- myc gene product is found mainly in actively proliferating neural tissues such as early development tissues or in retinoblastomas and neuroblastomas. In this report, the upstream region of mouse N- myc gene was ligated to pSVPCAT, which carries the simian virus 40 (SV40) promoter and bacterial chloramphenicol acetyltransferase (CAT) gene, and transcriptional activities were examined by CAT and S1 protection assays after transfection of the DNAs into human cervical carcinoma HeLa or neuroblastoma IMR32 cells. Several regulatory regions were identified: two promoting regions (−980 to −860 and −279 to +108) and an inhibiting one (−860 to −797). The region spanning positions −980 to −860 increased CAT expression independently of orientation and distance to the SV40 promoter, indicating that the element is a typical enhancer. Moreover, the expression levels from this enhancer were higher in IMR32 cells than in HeLa cells, indicating that action has, if not cell-type specificity, cell-type preference. These findings may provide useful bases for the understanding of the cell-type specific regulation of N- myc expression.