Variable Regulation of Sensitivity to Retinoic Acid-induced Differentiation in Wild-type and Retinoic Acid-resistant HL-60 Cells

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Abstract
The initial cell association and metabolic conversion of retinoic acid (RA) by HL-60 cells in serum-free, transferrin/insulin-supplemented, RPMI 1640 medium was ≥ 10-fold greater than in RPMI 1640 medium containing 10% fetal bovine serum (FBS). This was paralleled under the serum-free conditions by 10-fold greater sensitivity to RA-induced differentiation, which was partially reversed by the addition of purified bovine serum albumin to the same concentration present in 10% FBS. In serum-free HL-1 medium, HL-60 cell sensitivity to RA-induced differentiation was 250-fold less than in serum-free RPMI 1640 medium but, in this comparison, there was little difference in RA cell association or metabolism. A >200-fold RA-resistant HL-60 subline had RA cell-association and metabolism rates similar to those of wild-type cells under all culture conditions. No significant qualitative differences in the high performance liquid chromatography elution patterns of polar metabolites were observed under any circumstances. These results indicate that inherent cellular properties, not associated with gross differences in RA uptake or metabolism, primarily determined the relative sensitivity or insensitivity of HL-60 cells to RA-induced differentiation but that RA responsiveness was markedly regulated by extracellular factors, one of which, serum albumin, appeared to act by decreasing the initial cell association and metabolism of RA, whereas other, as yet unidentified exogenous factors, may have acted independently of these functions.

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