Transcriptional regulation of the N- myc gene: Identification of positive regulatory element and its double- and single-stranded DNA binding proteins

Abstract

The N- myc gene is amplified and overexpressed in neuroblastoma, retinoblastoma and small cell lung carcinoma, and is considered to be related to cell proliferation and/or differentiation. The transcriptional regulatory sequences of the c- myc gene have been already identified, while those of N- myc have remained obscure for a long time. In this report, we have identified several positive and negative transcriptional regulatory elements in the upstream region of the mouse N- myc gene. Among them, an activating sequence spanning −860 to −797 bp (63 bp) could be reduced to a functional core of 21 bp from −846 to −826. This sequence, termed N21 box, worked as a positive transcriptional element when linked directly upstream (but not downstream) of the putative N- myc promoter in HeLa, not in IMR32 cells. At least two proteins, of 42 kDa and 100 kDa, bound to the double-stranded N21 box, and were expressed in HeLa as well as in IMR32 cells. Moreover, the plus strand of N21 box could be specifically bound by a species of 42 kDa from either cell type and by a 37 kDa protein found only in HeLa cells. These proteins may be factors binding to positive transcriptional regulatory elements and may have a role in the regulation of N- myc expression.