Fetal isoform of human retinoic acid receptor β expressed in small cell lung cancer lines

The retinoic acid receptor type β (RAR β ) complementary DNA from a small cell tumor line was amplified, sequenced, and found to be homologous to the murine RAR β 1. Seventeen lung tumor lines were analyzed. Five of seven small cell lung carcinoma lines expressed RAR β 1, 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 RAR β 1. 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 RAR β 1. RAR β 1 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.