Differential effects of long-chain (sphingoid) bases on the monocytic differentiation of human leukemia (HL-60) cells induced by phorbol esters, 1 alpha, 25-dihydroxyvitamin D3, or ganglioside GM3.

Conditions were developed to prolong the ability of sphinganine, a potent inhibitor of protein kinase C, to block the phorbol ester-induced adherence of HL-60 cells beyond 24 h. The loss of inhibition after this time seen previously (A.H. Merrill, Jr., A.M. Sereni, V.L. Stevens, Y.A. Hannun, R.M. Bell, and J.M. Kinkade, Jr., J. Biol. Chem., 261: 12610-12615, 1986), which appeared to be due to metabolism of this long-chain base, was overcome by supplying sphinganine daily. After 4 days, phorbol myristate acetate-induced adherence was inhibited approximately 50% by sphinganine. Sphinganine significantly decreased the expression of nonspecific esterase induced by phorbol myristate acetate in the nonadherent cells, indicating that other aspects of maturation besides adherence were blocked. The effects of daily sphinganine treatments on the monocytic differentiation induced by 1 alpha-25-dihydroxyvitamin D3 or ganglioside GM3 were also investigated. The increases in nonspecific esterase expression, nitroblue tetrazolium reduction, and morphological maturation caused by either agent were unaffected by the long-chain base. In addition, the changes in several cell surface antigens caused by 1 alpha,25-dihydroxyvitamin D3 were unaltered by sphinganine. Although phorbol esters, 1 alpha,25-dihydroxyvitamin D3, and ganglioside GM3 all induce the maturation of HL-60 cells along the monocytic lineage, the finding that sphinganine only affected the differentiation initiated by phorbol esters, in which protein kinase C clearly is a major regulator, suggests that this enzyme does not play a major role in these other pathways of differentiation.