FETAL ISOFORM OF HUMAN RETINOIC ACID RECEPTOR-BETA EXPRESSED IN SMALL-CELL LUNG-CANCER LINES

The retinoic acid receptor type beta (RARbeta) complementary DNA from a small cell tumor line was amplified, sequenced, and found to be homologous to the murine RARbeta1. Seventeen lung tumor lines were analyzed. Five of seven small cell lung carcinoma lines expressed RARbeta1, but only one other line (epidermoid) expressed the isoform, and this was at trace levels. Two other epidermoid lines, as well as three adenocarcinoma, two adenosquamous, and two large cell-derived lines did not express RARbeta1. Nine adult human tissues, including lung, were analyzed, and in contrast to what has been reported for the mouse, undetectable or barely detectable levels were observed. On the other hand, a total of 13 different fetal tissues, at three different developmental stages, all expressed RARbeta1. RARbeta1 may be a master developmental gene in humans, and the remarkably specific association with small cell lung carcinoma suggests a molecular link between this type of cancer and development.