A novel cDNA clone (VDUP1) has been isolated from a cDNA library constructed from mRNA obtained from HL-60 cells stimulated by 1,25-dihydroxyvitamin D-3. Northern blot analysis showed that VDUP1 cDNA hybridizes to a 2.9 kb mRNA species which is up-regulated in HL-60 cells by 1,25-dihydroxyvitamin D-3 (1,25-(OH)2D3) treatment. In vitro expression of VDUP1 cDNA produced a 46 kDa protein. A search of the GenBank database revealed that the 3' untranslated region of VDUP1 is homologous to a sequence expressed in brain. A detailed time course study showed that the VDUP1 mRNA starts to increase at 6 h after 1,25-dihydroxyvitamin D-3 treatment, reaches a plateau at around 18 h and stays elevated for 24 h. The VDUP1 mRNA is not regulated by phorbol 12-myristate 13-acetate (PMA) in HL-60 cells. Inhibition of protein synthesis by cycloheximide does not prevent the induction of VDUP1 mRNA by 1,25-dihydroxyvitamin D-3. Cycloheximide itself increases VDUP1 mRNA levels. These results suggest that the degradation of VDUP1 mRNA is either translation-dependent or regulated by a labile protein.