Dual control of C-reactive protein gene expression by interleukin-1 and interleukin-6.

Human C-reactive protein (CRP) is the major acute phase reactant during acute inflammation. The human CRP promoter is expressed in an inducible and cell-specific manner when linked to the bacterial CAT gene and transfected into human hepatoma cell cultures. In this paper we analyze the effect of several recombinant cytokines or CRP promoter inducibility in human Hep3B cells. When cytokines are tested singly the major inducer of CRP-CAT fusions is interleukin-6 (IL-6). Maximal CAT gene expression, however, is only achieved when both interleukin-1 beta (IL-1 beta) and IL-6 are present. The response to the two cytokines is cooperative. Cooperativity is maintained when the CRP promoter is linked to a different coding region, that of the bacterial neomycin phosphotransferase II gene. With a series of 5' and 3' deletions we show the existence of two distinct and independent regions responsive to IL-6 and located upstream to the TATA box. The IL-1 effect is exerted at the level of downstream sequences that are probably important for optimal mRNA translatability or nuclear-cytoplasmic transport. Inducibility is not influenced by the activation of protein kinases C or A and does not require new protein synthesis.     

Upstream and intronic regulatory sequences interact in the activation of the glutamine synthetase promoter.

Glutamine synthetase (GS) is expressed at high levels in subsets of cells in some tissues and at low levels in all cells of other tissues, suggesting that the GS gene is surrounded by multiple regulatory elements. We searched for such elements in the 2.5-kb upstream region and in the 2.6-kb first intron of the GS gene, using FTO-2B hepatoma and C2/7 muscle cells as representatives of both cell types and transient transfection assays as our tools. In addition to the entire upstream region and entire intron, an upstream enhancer module at -2.5 kb, and 5', middle and 3' modules of the first intron were tested. The main effects of the respective modules and their combinatorial interactions were quantified using the analysis of variance (anova) technique. The upstream enhancer was strongly stimulatory, the middle intron module strongly inhibitory, and the 3'-intron module weakly stimulatory in both hepatoma and muscle cells. The 5'-intron module was strongly stimulatory in muscle cells only. The major new finding was that in both cell types, the upstream enhancer and 5'-intron module needed to be present simultaneously to fully realize their transactivational potencies. This interaction was responsible for a pronounced inhibitory effect of the 5'-intron module in the absence of the upstream enhancer in hepatoma cells, and for a strong synergistic effect of these two modules, when present simultaneously in muscle cells. The main difference between hepatoma and muscle cells therefore appeared to reside in tissue-specific differences in activity of the respective regulatory elements due to interactions rather than in the existence of tissue-specific regulatory elements.