Differential effects of chromosome 3p deletion on the expression of the putative tumor suppressor RAR beta and on retinoid resistance in human squamous carcinoma cells

Retinoids' effects on cell growth and differentiation are mediated by nucle ar retinoid receptors, which are ligand-activated transcription enhancing f actors. Because the expression of the retinoic acid receptor beta (RAR beta ) gene, which is located on chromosome 3p24, is diminished in premalignant and malignant tissues it has been proposed that it acts as a tumor suppress or. To test the hypothesis that RAR beta loss leads to retinoid resistance, we studied several karyotyped head and neck squamous carcinoma (HNSCC) cel l lines (UMSCC-17A, -17B, -22A, -22B, and -38) with deletion of one chromos ome 3p arm. RAR beta mRNA was neither detected nor induced by retinoic acid in these cells, whereas it was expressed and induced by retinoic acid in t wo other HNSCC cell lines (1483 and 183) without 3p deletion. Methylation o f the RAR beta gene promoter was detected in the 17B and 22B cells that fai led to express RAR beta but no methylation was found in 183A cells that did express RAR beta mRNA. Responsiveness of HNSCC cells to several retinoids in assays of growth inhibition and colony formation, was rank ordered as: 2 2B > 1483 > 38 > 183 > 17B. Additionally, retinoid response elements were t ransactivated in 22B more efficiently than in 17B cells. These results indi cate that loss of RAR beta expression does not necessarily lead to loss of growth inhibition by retinoids or to a block of retinoid signaling.