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Mol. Cell. Biol., 07 1995, 3945-3959, Vol 15, No. 7
N Moghal and BG Neel
Retinoic acid (RA) is required for normal airway epithelial cell growth and
differentiation both in vivo and in vitro. One of the earliest events
following the exposure of bronchial epithelial cells to RA is the strong
induction of RA receptor beta (RAR beta) mRNA. Previous work established
that many lung cancer cell lines and primary tumors display abnormal RAR
beta mRNA expression, most often absence or weak expression of the RAR beta
2 isoform, even after RA treatment. Restoration of RAR beta 2 into RAR
beta-negative lung cancer cell lines has been reported to inhibit
tumorigenicity. Since RAR beta 2 inactivation may contribute to lung
cancer, we have investigated the molecular mechanism of defective RAR beta
2 expression. Nuclear run-on assays and transient transfections with RAR
beta 2 promoter constructs indicate the presence of trans-acting
transcriptional defects in most lung cancer cell lines, which map to the RA
response element (RARE). These defects cannot be complemented by
RAR-retinoid X receptor cotransfection and can be separated into two types:
(i) one affecting transcription from direct repeat RAREs, but not
palindromic RAREs, and (ii) another affecting transcription from both types
of RARE. Studies using chimeras between RAR alpha, TR alpha, and other
transcription factors suggest the existence of novel RAR-thyroid hormone
receptor AF- 2-specific cofactors, which are necessary for high levels of
transcription. Furthermore, these factors may be frequently inactivated in
human lung cancer.
Copyright © 1995, American Society for Microbiology
Evidence for impaired retinoic acid receptor-thyroid hormone receptor AF-2 cofactor activity in human lung cancer
Molecular Medicine Unit, Beth Israel Hospital, Boston, Massachusetts, USA.
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