G1 accumulation caused by iron deprivation with deferoxamine does not accompany change of pRB status in ML-1 cells.

We analyzed G1 accumulation induced by the iron chelator deferoxamine B mesylate (DFO) compared it with that caused by etoposide and cytosine arabinoside (AraC). The results showed that p53 protein increased with all three treatments without an increase in p53 mRNA. After treatment for 3 or 6 h, p21 mRNA increased with 10(-4) DFO to 159% or 556% of pretreatment levels, to 509% or 391% with 10(-5) etoposide, and to 263% or 304% with 10(-5) AraC. Induction of p21 protein was not observed with fluorescence activated cell sorting and Western blot analysis after treatment with DFO or AraC. Treatment with DFO did not cause any change in levels of CDK4 mRNA or protein, whereas etoposide or AraC treatment did diminish CDK4 protein. Enzyme linked immunosorbent assay for pRB and its phosphorylation, which reflects CDK4 activity, revealed that treatment with DFO did not change the amount of pRB or the phosphorylation status. Results of this investigation show that the mechanism of G1 accumulation induced by DFO involves a p53-independent pathway and that expression of p21 protein may be regulated posttranscriptionally.