Regulation of the human ApoA-II gene by the synergistic action of factors binding to the proximal and distal regulatory elements

We have recently shown that the human apoA-II promoter contains a set of 11 distal regulatory elements between nucleotides -903 and -255 and three proximal regulatory elements between nucleotides -126 and -33 that are essential for hepatic and intestinal transcription of the apoA-II gene (Chambaz, J., Cardot, P., Pastier, D., Zannis, V. I., and Cladaras, C. (1991) J. Biol. Chem. 266, 11676-11685). Deletion or nucleotide substitution analysis has shown that alterations in elements L (nucleotides -803 to -773) and K (nucleotides -760 to -743) reduced hepatic transcription to 25 and 20% and intestinal transcription to 8 and 4% of control, respectively, as measured by chloramphenicol acetyltransferase assays, indicating that these elements play an important regulatory role. Nucleotide substitutions in element AB (nucleotides -65 to -33) reduced hepatic and intestinal transcription to 60 and 36% of control, respectively. The factors that recognize regulatory regions L, K, and AB were analyzed by DNA binding gel electrophoretic and competition assays. This analysis has shown that elements AB, K, and L bind with different affinities to a newly characterized heat-stable factor, CIIIB1, which is a transcriptional activator of the human apoC-III gene (Ogami, K., Kardassis, D., Cladaras, C., and Zannis, V. I. (1991) J. Biol. Chem. 266, 9640-9646). In addition, elements AB and K bind a heat-labile activity, designated AIIAB1, and element L binds to several CCAAT box binding activities. Mutations in domain L that prevented the binding of CCAAT box binding activities reduced both hepatic and intestinal transcription to 30% of control, indicating the importance of these factors in transcription. Simultaneous nucleotide substitutions that prevented the binding of CIIIB1 activity in elements AB, K, and L reduced hepatic and intestinal transcription to 7 and 6% of control, respectively, suggesting that the synergistic interaction of CIIIB1 (bound to the proximal and distal regulatory elements) with CCAAT box proteins (bound to element L) can modulate the level of transcription of the human apoA-II gene.