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  • Title: Different ligand responsiveness of human retinoic-acid-receptor beta-gene transcription in tumorigenic and non-tumorigenic cervical-carcinoma-derived cell lines is mediated through a large retinoic-acid-response domain.
    Author: Baust C, Redpath L, Schwarz E.
    Journal: Int J Cancer; 1996 Jul 29; 67(3):409-16. PubMed ID: 8707417.
    Abstract:
    The retinoic-acid-receptor beta gene (RAR-beta) encodes a suspected tumor suppressor for several types of human carcinomas. RAR-beta transcription is induced by retinoic acid (RA) through retinoid receptors which bind as heterodimers of a RA-activated RA receptor (RAR) and a retinoid X receptor to the RA-responsive element in the RAR-beta promoter region (beta RARE). RA inducibility of RAR-beta gene expression is often lost or reduced in human carcinoma cells. As previously shown, the RAR-beta gene is highly RA-inducible in nontumorigenic HeLa x fibroblast hybrid cells, but neither in HeLa cervical carcinoma cells nor in a tumorigenic hybrid segregant line. We report here that severe reduction of RA-induced RAR-beta mRNA levels is a general feature of tumorigenic HeLa x fibroblast segregants. To study the molecular basis of differential RA inducibility, we have performed transient transfection assays in HeLa and nontumorigenic 444 hybrid cells using reporter constructs with different 5' and internal deletions of the RAR-beta transcription-control region. Remarkably, maximal RA inducibility in 444 cells required the integrity of the complete RAR-beta upstream region. In HeLa cells, all reporter constructs showed only low RA inducibility levels. The differential RA inducibility in 444 and HeLa cells could be conferred by the RAR-beta upstream region, but not by subfragments of it, on a heterologous RA-responsive promoter. The data indicate that maximal RA inducibility of RAR-beta gene transcription in nontumorigenic 444 cells depends on the cooperation of the beta RARE with additional upstream elements. All elements together constitute a large RA response domain as the higher-order transcription control unit. The communication between the upstream elements and the beta RARE seems to be disturbed in HeLa cells. Similar defects may be responsible for the loss of RA responsiveness of RAR-beta gene expression in other human tumors.
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