A DIFFERENTIAL SCREEN FOR LIGAND-REGULATED GENES - IDENTIFICATION OF HOXA10 AS A TARGET OF VITAMIN-D-3 INDUCTION IN MYELOID LEUKEMIC-CELLS

1,25-Dihydroxyvitamin D-3 [1,25(OH)(2)D-3], the hormonal ligand for vi tamin D-3, is a potent inducer of myeloid-leukemic-cell differentiatio n. Such cells differentiate exclusively into monocytes/macrophages in response to this ligand, Since 1,25(OH)(2)D-3 transduces its hormone s ignal through the vitamin D, receptor (VDR), a ligand modulated transc ription factor and member of the nuclear hormone receptor superfamily, we sought to identify direct VDR target genes induced during this dif ferentiation process, To do so, we applied a modified differential scr een with a nascent-RNA purification strategy using biases for immediat e-early-response genes induced by 1,25(OH)(2)D-3 in the myelomonocytic cell line U937, Using this screen, we had previously identified p21(W af1/Cip1) as a gene transcriptionally induced by 1,25(OH)(2)D-3 and de monstrated that this induction facilitates the differentiation of U937 cells into monocytes/macrophages (24). Here, we describe in detail ou r differential screen strategy and the identification and isolation of 20 1,25(OH)(2)D-3-inducible genes or unknown cDNAs by means of this s creen, One gene newly identified as a target of VDR regulation in myel oid cells is the homeobox HoxA10 gene, HoxA10 protein may act as a gen eral regulator of cell growth, since overexpression of HoxA10 facilita ted the differentiation of U937 cells into monocytes/macrophages indep endent of 1,25(OH)(2)D-3 and acted to strongly inhibit the growth of t he breast cancer cell line MCF-7 by arresting these cells in G(1).