Wild-Type Human p53 and a Temperature-Sensitive Mutant Induce Fas/APO-1 Expression

Abstract

Fas/APO-1 is a cell surface protein known to trigger apoptosis upon specific antibody engagement. Because wild-type p53 can activate transcription as well as induce apoptosis, we queried whether p53 might upregulate Fas/APO-1. To explore this possibility, we examined human p53-null (H358 non-small-cell lung adenocarcinoma and K562 erythroleukemia) and wild-type p53-containing (H460 non-small-cell lung adenocarcinoma) cell lines. When H358 or H460 cells were transduced with a replication-deficient adenovirus expression construct containing the human wild-type p53 gene but not with vector alone, a marked upregulation (approximately a three-to fourfold increase) of cell surface Fas/APO-1 was observed by flow cytometry. Similarly, K562, cells stably transfected with a plasmid vector containing the temperature-sensitive human p53 mutant Ala-143 demonstrated a four- to sixfold upregulation of Fas/APO-1 by flow-cytometric analysis at the permissive temperature of 32.5 degrees C. Temperature-sensitive upregulation of Fas/APO-1 in K562 Ala-143 cells was verified by immunoprecipitation and demonstrated to result from enhanced mRNA production by nuclear run-on and Northern (RNA) analyses. Stably transfected K562 cells expressing temperature-insensitive, transcriptionally inactive p53 mutants (His-175, Trp-248, His-273, or Gly-281) failed to upregulate Fas/APO-1 at either 32.5 degrees or 37.5 degrees C. The temperature-sensitive transcription of Fas/APO-1 occurred in the presence of cycloheximide, indicating that de novo protein synthesis was not required and suggested a direct involvement of p53. Collectively, these observations argue that Fas/APO-1 is a target gene for transcriptional activation by p53.

Combination with SGT-53 overcomes tumor resistance to a checkpoint inhibitor

“…Increased FAS expression with SGT-53 treatment could also increase CTL-mediated apoptosis of tumor cells since CTLs use FAS/FAS ligand binding to induce apoptosis of target cells during the CTL-tumor cell interaction. 36,37 These observations recapitulate previous findings, 20,21,38–40 and it is reasonable to believe that elevated expression of these component of immunogenicity would be instrumental in achieving efficient anti-tumor immune responses.…”

Down-regulation of Fas gene expression in colon cancer is not a result of allelic loss or gene rearrangement

“…The p53 protein is generally believed to be responsible for induction of apoptosis in response to DNA damage, however loss of p53 is a comparatively late event in colorectal tumorigenesis (Fearon and Vogelstein, 1990). The molecular targets of p53 that carry out the apoptotic signal are unknown, however p53 can bind to the promoter of the Fas gene and induce its expression (Owen-Schaub et al, 1995). If Fas is a downstream effector of p53, its loss could directly influence cell death in colonic tumours.…”

Protein serine/threonine phosphatase-1 dephosphorylates p53 at Ser-15 and Ser-37 to modulate its transcriptional and apoptotic activities

“…As a master regulator of apoptosis in different cells, p53 regulates apoptosis by two mechanisms. First, it acts as a transcriptional factor to regulate expression of many genes involved in apoptosis (Miyashita et al, 1994;Buckbinder et al, 1995;Miyashita and Reed, 1995;Wen-Schaub et al, 1995;Israeli et al, 1997;Polyak et al, 1997;Wu et al, 1997;El-Deiry, 1998). Second, it can activate Bax in mitochondria to antagonize the antiapoptotic ability of Bcl-2 and Bcl-XL (Mihara et al, 2003;Schuler and Green, 2005).…”