Retinoids and their receptors [retinoic acid receptors (RARs) and retinoid X receptors] play an important role in maintaining the balance between proliferation and apoptosis. Recently, Deng et al. [Science (Washington DC), 274: 2057–2059, 1996] reported a loss of heterozygosity on chromosome 3p24 in breast cancer specimens and the morphologically normal appearing adjacent tissue. The 3p24 locus includes, among other genes, the region coding for RAR-β. This study was designed to determine whether there are abnormalities in the expression of retinoid receptors in surgical specimens of patients with breast cancer.
In 14 patients, transcripts of nuclear retinoid receptors were detected by in situ hybridization in formalin-fixed, paraffin-embedded specimens by means of digoxigenin-labeled riboprobes specific for RAR-α, -β and -γ.
We found RAR-α expressed in all specimens, whereas RAR-γ was expressed in 100% of normal breast tissue but in only 11 of 14 tumorous lesions. RAR-β was found in all cases of normal breast tissue localized distant from the tumor, but in 13 of 14 cases it was completely absent in the tumor and the morphologically normal appearing tissue adjacent to the tumor. One possibility to explain the suppression of RAR-β is a mutation in the promoter region. Sequencing the DNA extracted from paraffin-embedded tumor tissue of the corresponding breast cancer specimens, we were not able to detect any mutation in the retinoic acid-responsive element.
Our results clearly indicate a crucial role of RAR-β in the carcinogenesis of breast cancer.
This work was supported by Jubiläumsfonds der Österreichischen Nationalbank Project 5788 and by a grant from the Fonds zur Förderung der wissenschaftlichen Forschung.