p53 Activates Either Survival or Apoptotic Signaling Responses in Lupulone-Treated Human Colon Adenocarcinoma Cells and Derived Metastatic Cells.

The SW480 cell line is derived from a human colon adenocarcinoma, and SW620 cells are derived from a lymph node metastasis of the same patient. We have previously shown that lupulone induces apoptosis in SW480 cells, through a cross talk between the TRAIL-death receptor pathway and the mitochondrial apoptotic pathway. In SW620 cells, lupulone induced apoptosis only through TRAIL-death receptor activation. Both cell lines exhibit the same p53 mutations. Because p53 plays a central role in the response to cellular stresses by upregulating the transcription of several genes controlling apoptosis, we aimed to study the involvement of p53 on lupulone-triggered apoptosis. Our data show that in SW620 cells, lupulone upregulated p53 gene expression and caused a cloistering of p53 in the nucleus, allowing p53 to play a proapoptotic role by activating the TRAIL-death receptor pathway. In contrast, in lupulone-treated SW480 cells, p53 was translocated to the cytoplasm where it initiated a survival response associated with the up-regulation of antiapoptotic Bcl-2 and Mcl-1 proteins in an attempt to preserve mitochondrial integrity. These prosurvival effects of p53 in lupulone-treated SW480 cells were reversed by pifithrin-α, an inhibitor of p53 function, which caused a blocking of p53 in the nucleus leading to the down-regulation of Bcl-2 and Mcl-1, the up-regulation of proapoptotic Bax protein and TRAIL-death receptors leading to enhanced cell death. Our data support different functions of the same mutated p53 in colon adenocarcinoma and derived metastatic cells in response to the chemopreventive agent lupulone.