Enhanced messenger RNA stability and differentiation of HL 60 cells treated with 1,25-dihydroxyvitamin D3 and cordycepin.

The effect of inhibitors of RNA synthesis on 1,25(OH)2 vitamin D3-induced monocytic differentiation was studied in a well-differentiating clone AB 47 of HL 60 cells. The concentrations of these inhibitors were chosen to permit the maintenance of cell viability for at least 48 hours, and resulted in 40-60% inhibition of total cellular RNA synthesis. No impairment of 1,25(OH)2 vitamin D3-induced monocytic differentiation was observed with all inhibitors tested, and the presence of cordycepin actually enhanced differentiation. The phenotypic evidence of monocytic differentiation correlated with the increased levels of mRNA for c-fos and c-fms measured by hybridization to appropriate nick-translated cDNA probes. In contrast, nuclear run-on experiments showed the expected inhibition of transcription of these genes by the compounds used. The data suggest that interference by external agents with transcription of genes essential for a differentiation program brings into play compensatory mechanisms which permit the program to continue. Thus, differentiation appears to have a high priority among various competing intracellular pathways in 1,25(OH)2 vitamin D3-treated HL 60 cells. Stabilization of messenger RNA levels evident in this study may therefore represent a general cellular mechanism for the correction of unwanted effects of xenobiotics on the cell.