Expression of Retinoic Acid Receptor Alpha mRNA in Human Leukemia Cells

The expression of the newly described human retinoic acid receptor alpha (RARα) in six nonlymphoid and six lymphoid leukemia cell lines and nine freshly obtained samples of leukemia cells from patients with acute nonlymphoid leukemia was assessed by Northern blot analysis, using a full length cDNA clone of RARα as probe. RARa was expressed in all 12 cell lines and in all fresh leukemia samples as two major transcripts of 2.6 and 3.5 kb in size. Levels of RARa expression and transcript sizes in retinoid-sensitive cells (such as HL60 or fresh promyelocytic leukemia cells) were not different from those in other samples. Moreover, expression of RARα was not significantly modulated by exposure to cis-retinoic acid (cisRA) in either cisRA- responsive or unresponsive cells. By using a 3' fragment of the RARα gene as a probe, we confirmed that the transcripts visualized did not represent the homologous RARβ gene. RARα appears to be expressed in most human leukemia cells regardless of the type of biologic response to retinoic acid.