The putative mechanism of cell cycle exit in APL cells upon the effect of ATRA.

p21^WAF1/CIP1 may function at the upstream differentiation program initiation. Members of the CEBP family, such as CEBP-ε and GADD153 (CHOP), may stabilize the p21^WAF1/CIP1 protein from degradation in the current context. The additional member of this family, CEBP-α, has been reported to be implicated in the differentiation of preadipocytes through posttranscriptional stabilization of the p21^WAF1/CIP1 protein (left). Additionally, activation of the cell cycle exit and apoptosis-resistant pathways appears to be the prerequisite for the initiation of the differentiation program.