Regulation of the multiple promoters of the human aldolase A gene: response of its two ubiquitous promoters to agents promoting cell proliferation.

The human aldolase A gene is transcribed from three distinct promoters, the two ubiquitous promoters PN and PH and the muscle specific promoter PM. In the present study, we investigate further aldolase A mRNA structure and expression. We demonstrate that the upstream N-type exon is, in fact, extremely heterogeneous. RNAse H mapping experiments permit quantification of relative abundance of N, M, and H type mRNAs and show that the level of transcripts containing the downstream H-type exon is at least 30 times higher than that of those containing N exon, in all tissues tested. Aldolase A level is up-regulated in proliferating cells. Here we show that both N and H type mRNAs, although barely detectable in normal liver, are highly expressed in human hepatomas biopsies. Furthermore, in human lymphocytes, N-type mRNA level is enhanced by serum treatment, while in cultured Hep G2 cells, both N-type and H-type mRNA levels are increased by serum and by the tumor promoting agent PMA. Using CAT constructs in transfection experiments, we demonstrate that the H exon plus its upstream region can function autonomously: the 420 base pairs upstream of the H exon are sufficient to confer to promoter PH an efficiency comparable that of the complete SV40 early promoter and enhancer in two cell lines.