Identification of an AP-1-like sequence in the promoter region of calcyclin, a S-100-like gene. Enhancement of binding during retinoic acid-induced neuroblastoma cell differentiation.

The promoter region of genes involved in cell growth and differentiation is bound by specific transcription factors which regulate its expression. Our previous study showed that the calcyclin gene, which belongs to the large family of Ca2+-binding proteins, is differently expressed in SK-N-BE(2)C and LA-N-5 neuroblastoma cell lines. We analysed the region upstream the transcription initiation site of the gene before and during retinoic acid (RA)-induced differentiation. Gel-shift analysis showed that the -161,-135 untranslated region is bound by an AP-1-like protein both in SK-N-BE(2)C and LA-N-5 cells. Competition assay demonstrated that AP-2,AP-3 and NF1 transcription factors did not bind in the same region. Calcyclin mRNA is induced in RA-treated LA-N-5 cells and reaches maximal expression at 96 h, suggesting that its gene is involved in cell differentiation. Gel-shift analysis shows a strong signal of binding after 96 h of RA treatment. Our results indicate that RA induces an increase in the binding protein or improves its affinity for the AP-1-like region during neuronal differentiation. These preliminary data suggest that the calcyclin gene is involved in neuronal pathway differentiation and that AP-1-like binding sequence could be one of the gene regions that is under transcriptional factor control during cell differentiation.