REPRESSION OF INTERLEUKIN-2 AND INTERLEUKIN-4 PROMOTERS BY TUMOR-SUPPRESSOR PROTEIN P53

Interleukin 2 (IL-2) and interleukin 4 (IL-4) secreted by activated bu t not by resting mature T cells are pleiotropic cytokines affecting gr owth and differentiation of diverse cell types, such as T cells, B cel ls, and mast cells, There is little information about the molecular ba sis for the constitutive repression of IL-2 and IL-4 gene expression i n unstimulated T cells, We investigated the possibility that wild-type (wt) p53, a nuclear tumor suppressor protein, might serve to repress IL-2 and IL-4 gene expression in murine E14 T lymphoma and in human Ju rkat cells, We transiently cotransfected these cells with constitutive simian virus 40 (SV 40) early promoter expression plasmids overproduc ing wt or mutant murine p53 and with appropriate luciferase (luc) repo rter plasmids containing the promoter elements of murine IL-2 and IL-4 genes to evaluate the effect of various p53 species on these promoter s, Murine wt p53 derived from pSG5p53cD strongly repressed the IL-2 an d IL-4 promoters in both cell lines induced by the phorbol ester TPA a nd the Ca2+ ionophore ionomycin but not, however, in uninduced cells, In similar transient transfection experiments with lymphoma cells, ove rexpression of deletion mutant species of murine p53 revealed that the N-terminal and C-terminal domains are crucial for inhibition of both IL-2 and IL-4 gene expression, These parts of p53 comprise the transac tivation domain at the amino terminal side, which has previously also been shown to interact with the TATA-box binding-protein TBP and the c arboxy-terminal oligomerization domain, Additionally, it was shown tha t a previously described inhibitory protein, the high-mobility-group p rotein HMG-I/Y, does not functionally interact with p53, Cotransfectio n of expression plasmids for both p53 and HMG-I/Y did not alter the ex tent of inhibition by the individual proteins, These data suggest that p53 can downmodulate both IL-2 and IL-3 gene expression and that both the transactivation and oligomerization domains of the tumor suppress or protein are essential for this transcriptional repression.