CD43 (leukosialin, sialophorin), a cell surface protein on most hematopoietic 
cells, is an important regulator of immune cell function and is involved in 
regulation of cell adhesion and proliferation. Aberrant expression of CD43 is a 
common event observed in human tumors of non-hematopoietic origin suggesting a 
role in tumor development. We have previously shown that overexpression of CD43 
causes activation of the ARF-p53 tumor-suppressor pathway and results in cell 
death. In a non-functional ARF-p53 background, the cells overexpressing CD43 
display an increased cell growth rate due to higher survival. Here we show that 
p53 specifically downregulates the expression of CD43 at the protein and mRNA 
level. Transactivating properties of p53 are necessary to affect the expression 
of exogenous CD43. The downregulation of CD43 mRNA is caused by p53-dependent 
transrepression, at least in part, via a histone deacetylation mechanism. These 
studies establish that under certain conditions there exists a negative feedback 
loop between p53 and CD43: CD43-dependent signaling activates p53, which in turn 
downregulates the expression of CD43.