MODULATION OF P53, WAF1 P21 AND BCL-2 EXPRESSION DURING RETINOIC ACID-INDUCED DIFFERENTIATION OF NB4 PROMYELOCYTIC CELLS/

The NB4 cell line, established from a patient with APL, carries the t( 15;17) and undergoes differentiation along the granulocytic pathway wh en exposed to retinoic acid (RA). The NB4 cell line was used as a mode l for exploring the expression of genes and proteins implicated in gro wth regulation, differentiation and apoptosis during treatment with RA . NB4 cells undergo a series of cytological and molecular alterations during RA treatment--Day 1: cell differentiation marked by an increase in CD11b is evident. Day 2: WAF1/p21 mRNA and then protein rise, thou gh they drop 2 days later. Day 3: the percentage of cells in S phase b egins to decrease and G1 arrest begins. Day 4: p53 mRNA level and then protein levels fall. Day 5: CD11b/BCL-2 double staining cells are mar kedly reduced. No signs of apoptosis were observed after up to 8 days of treatment with RA. These results demonstrate that NB4 cells treated with RA rapidly differentiate and arrest at G1 phase concurrent with p53-independent WAF1/p21 induction; in addition, phenotypic differenti ation appears to commence before changes in cell cycle progression. An explanation for the decrease in p53 as well as the lack of apoptosis immediately after BCL-2 downregulation will require further study. (C) 1997 Elsevier Science Ltd.