Cell type-specific transcription of the alpha 1(VI) collagen gene - Role of the AP1 binding site and of the core promoter

Analysis of the chromatin of different cell types has identified four DNase I-hypersensitive sites in the 5'-flanking region of the alpha 1(VI) collag en gene, mapping at -4.6, -4,4, -2,5, and -0.1 kilobase (kb) from the RNA s tart site. The site at -2.5 kb was independent from, whereas the other thre e sites could be related to, alpha 1(VI) mRNA expression, The site at -0.1 kb was present in cells expressing (NIH3T3 and C2C12) but absent in cells n ot expressing (EL4) the mRNA; the remaining two sites were apparently relat ed with high levels of mRNA. DNase I footprinting and gel-shift assays with NIH3T3 and C2C12 nuclear extracts have located a binding site for transcri ption factor AP1 (activator protein 1) between nucleotides -104 and -73, Wh en nuclear extracts from EL4 lymphocytes were used, the AP1 site-containing sequence was bound by proteins not related to AP1, The existence of the hy persensitive site at -0.1 kb may be related to the binding of AP1 and of ad ditional factors to the core promoter (Piccolo, S,, Bonaldo, P,, Vitale, P. , Volpin, D,, and Bressan, G, M, (1995) J. Biol, Chem. 270, 19583-19590), T he function of the AP1 binding site and of the core promoter in the transcr iptional regulation of the Col6a1 gene was investigated by expressing sever al promoter-reporter gene constructs in transgenic mice and in cell culture s. The results indicate that regulation of transcription of the Col6a1 gene by different cis-acting elements (core promoter, AP1 binding site and enha ncers) is not completely modular, but the final output depends on the speci fic interactions among the three elements in a defined cell type.