THE ROLE OF A 70-KDA NUCLEAR-PROTEIN IN FETAL HEMOGLOBIN-SYNTHESIS INK562 CELLS

Previously, we reported that a 70 kDa nuclear protein may regulate fet al haemoglobin gene expression in haemin treated K562 cells. To obtain further evidence of the specific role of this 70 kDa nuclear protein, we compared the nuclear fractions isolated from phenylacetate, hydrox yurea and haemin treated K562 cells. Both phenylacetate and hydroxyure a have been used to induce fetal haemoglobin synthesis in K562 cells. Cell growth was measured by biochemical events including DNA, RNA and protein synthesis. Differentiation of K562 cells was determined by bot h [H-3]-leucine incorporation into fetal haemoglobin and scoring benzi dine-stained positive cells. Unlike the haemin treated cells, phenylac etate and hydroxyurea induced growth arrest and increased fetal haemog lobin gene expression in K562 cells. After four days of treatment with phenylacetate and hydroxyurea more than 50% of the cells stained posi tive with benzidine. The SDS-Polyacrylamide gel electrophoretic analys is of nuclear proteins isolated from phenylacetate and hydroxyurea tre ated K562 cells showed that the 70 kDa protein was reduced in nuclear protein extract in both groups similar to haemin treated cells. These results suggest that the loss of the 70 kDa protein from a nuclear pro tein extract is not restricted to only haemin treated cells but also o ccurs in hydroxyurea and phenylacetate treated cells. Our results prov ide further evidence that the 70 kDa nuclear protein may be involved i n regulating fetal haemoglobin expression through a negative control m echanism.