Dibutyryl cAMP enhances the effect of 1,25-dihydroxyvitamin D3 on a human promyelocytic leukemia cell, HL-60, at both the receptor and the postreceptor steps.
1,25-Dihydroxyvitamin D3 (1,25-(OH)2D3) induces differentiation of a human promyelocytic leukemia cell line, HL-60, into monocytes/macrophages, and 25-hydroxyvitamin D3- and 1,25-(OH)2D3-24-hydroxylase activities in HL-60 mitochondria via a steroid-hormone receptor mechanism. Dibutyryl cyclic adenosine monophosphate (dbcAMP), a granulocyte inducer, significantly augmented the differentiation-inducing effect of 1,25-(OH)2D3 along the monocyte/macrophage pathway. Furthermore, dbcAMP significantly potentiated the effect of 1,25-(OH)2D3 on HL-60 cells to hydroxylate 1,25-(OH)2[26,27-3H]D3 to form 1,24,25-(OH)3[26,27-3H]D3. DbcAMP seemed to augment the effect of 1,25-(OH)2D3 in part through upregulation of the 1,25-(OH)2D3 receptor, because 10(-7) M dbcAMP increased 1,25-(OH)2D3 receptor levels approximately 2.3-fold, which was similar to a 1.9-fold augmentation by the same concentrations of dbcAMP of 1,25-(OH)2D3-induced cell characteristics to hydroxylate C-24 of 1,25-(OH)2[26,27-3H]D3. However, dbcAMP is also known to enhance HL-60 cell differentiation caused by other differentiation inducers. We have established another HL-60 clone which acquires resistance to 1,25-(OH)2D3 in the induction of cell differentiation by a defect at the postreceptor step, as reflected by resistance to other differentiation inducers, such as retinoic acid and dimethyl sulfoxide. Even in this resistant clone, dbcAMP significantly enhanced the differentiation-inducing effect of 1,25-(OH)2D3. Of interest, this clone showed resistance to dbcAMP in the induction of cell differentiation. Furthermore, we have demonstrated that intracellular cAMP levels were significantly lower in uremic serum-treated cells than in cells treated with normal human serum and that a significant positive correlation was found between intracellular cAMP levels and 1,25-(OH)2D3-induced cell differentiation. These data indicated that the intracellular cAMP level is one of the major determinants of 1,25-(OH)2D3-induced HL-60 cell differentiation and that dbcAMP could enhance the effects of 1,25-(OH)2D3 on HL-60 cells not only by increasing 1,25-(OH)2D3 receptor levels but also at the postreceptor step.
Inaba
M
M
Second Department of Internal Medicine, Osaka City University Medical School, Japan.
Okuno
S
S
Koyama
H
H
Nishizawa
Y
Y
Morii
H
H
D003994:Bucladesine / Q000008:administration & dosage*; D002117:Calcitriol / Q000008:administration & dosage*; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D000242:Cyclic AMP / Q000378:metabolism; D003577:Cytochrome P-450 Enzyme System; D004351:Drug Resistance; D004357:Drug Synergism; D006801:Humans; D066298:In Vitro Techniques; D015473:Leukemia, Promyelocytic, Acute / Q000503:physiopathology*; D018167:Receptors, Calcitriol; D011987:Receptors, Steroid / Q000378:metabolism; D013250:Steroid Hydroxylases / Q000378:metabolism; D014407:Tumor Cells, Cultured; D065668:Vitamin D3 24-Hydroxylase
D018167:Receptors, Calcitriol; D011987:Receptors, Steroid; D003994:Bucladesine; D003577:Cytochrome P-450 Enzyme System; D000242:Cyclic AMP; D013250:Steroid Hydroxylases; D065668:Vitamin D3 24-Hydroxylase; D002117:Calcitriol