1-ALPHA,25-DIHYDROXYVITAMIN D-3-INDUCED UP-REGULATION OF CALCINEURIN DURING LEUKEMIC HL-60 CELL-DIFFERENTIATION

Cyclosporin A and FK506, at concentrations that inhibited phosphatase activity of calcineurin in HL-60 cellular lysates, augmented the proli feration of leukemic HL-60 cells, These immunosuppressants did not aff ect 1 alpha,25-dihydroxyvitamin D-3 [1,25(OH)(2)D-3]-induced monocytic differentiation of HL-60 cells, but did abrogate the 1,25(OH)(2)D-3-i nduced inhibition of HL-60 cell growth. Treatment with 20 nmol/L 1,25( OH)(2)D-3 led to a progressive increase in calcineurin phosphatase act ivity in subcellular fractions from HL-60 cell extracts; the increase in this activity appeared to parallel the phenotypic and functional ch anges of HL-60 cells during monocytic differentiation induced by 1,25( OH)(2)D-3. Immunoblot analysis indicated that increase in calcineurin activity was concordant with the increased expressions of calcineurin catalytic subunit isozymes, calcineurin A alpha(CNA alpha), and calcin eurin A beta(CNA beta), and a regulatory calcineurin B subunit (CNB) p roteins, which were preceded by a coordinate increase in the levels of CNA alpha, CNA beta and CNB mRNAs. The expression of calmodulin remai ned unaltered throughout 1,25(OH)(2)D-3-induced monocytic differentiat ion. These results suggest that calcineurin activation has a net negat ive effect on HL-60 cell proliferation, and that the increased express ion of calcineurin may be involved in 1,25(OH)(2)D-3-induced inhibitio n of HL-60 cell proliferation. (C) 1996 by The American Society of Hem atology.