Down-regulation of nucleophosmin/B23 during retinoic acid-induced differentiation of human promyelocytic leukemia HL-60 cells

Abstract

Human promyelocytic leukemia HL-60 cells were induced to undergo granulocytic di erentiation by treatment with retinoic acid (RA, 10 mM, 1 ± 5 days). The steady-state level of nucleophosmin/B23 mRNA decreased during the RA-induced di erentiation. There was also decrease in the level of total cellular nucleophosmin/B23 protein during the RA-induced di erentiation. Stabilization and nuclear run-on assays indicate that the decrease in nucleophosmin/B23 mRNA in RA-treated HL-60 cells was transcriptionally regulated. Unlike c-myc mRNA, there was virtually no decline of nucleophosmin/B23 mRNA during the growth arrest by serum-starvation. The decrease in nucleophosmin/B23 mRNA expression in HL-60 cells subsequent to retinoic acid treatment can thus be attributed to cellular di erentiation rather than the growth arrest induced by RA. Nucleophosmin/B23 antisense oligomer treatment signi®cantly potentiated RA-induced cellular di erentiation. Results of this study suggest that nucleophosmin/ B23 is one of the key elements in the down-regulation of nucleolar function for cellular di erentiation.

Mortalization of human promyelocytic leukemia HL-60 cells to be more susceptible to sodium butyrate-induced apoptosis and inhibition of telomerase activity by down-regulation of nucleophosmin/B23

“…There was signi®cant decrease in mRNA level of nucleophosmin/B23 in the cells treated with nucleophosmin/B23 antisense oligomer as compared to the control untreated cells (previously shown, Hsu and Yung, 1998). Nucleophosmin/B23 antisense oligomer treatment potentiated BuONa-induced (1 mM, 24± 96 h) inhibition of cell growth ( Figure 8a) and induction of apoptosis (Figure 8b,c).…”

“…A decline of telomerase activity in BuONa-treated versus untreated was observed over time (Figure 6 Little changes in nucleophosmin/B23 mRNA expression and telomerase activity after growth arrest without apoptosis HL-60 cells do arrest growth when deprivated of serum from the growth medium. In serum growth-arrested cells, the abundance of nucleophosmin/B23 mRNA (previously shown, Hsu and Yung, 1998) and the telomerase activity did not change ( Figure 7). In contrast to the decrease of c-myc mRNA expression…”

“…The ®gure is a representative of the results obtained in at least three independent experiments. Points, means of triplicates in serum-starved HL-60 cells (Hsu and Yung, 1998) or in previous study in F9 cells (Dean et al, 1986), the decline of the expression of nucleophosmin/B23 mRNA and the down-regulation of telomerase activity are rather related to induced-apoptosis than the growth arrest during the treatment with BuONa/vanadate.…”

“…Down-regulation of telomerase activity (Bestilny et al, 1996) and nucleophosmin/B23 mRNA (Hsu and Yung, 1998) are observed in response to differentiation-inducing agent retinoic acid in HL-60 cells. The aim of our present study is therefore to elucidate the possible correlation between regulation of nucleophosmin/B23 and cell immortalization.…”

“…Our recent ®ndings demonstrate that nucleophosmin/B23 is transcriptionally down-regulated during retinoic acid (RA) induced cellular di erentiation of HL-60 promyelocytic leukemia cells (Hsu and Yung, 1998). The potentiation of RA-induced di erentiation by nucleophosmin/B23 antisense oligomer further implicates that nucleophosmin/B23 plays an important role in the down regulation of nucleolar function for cellular di erentiation.…”