p53 down-regulates human bradykinin B1 receptor gene expression

Area of Science:

• Molecular Biology
• Gene Regulation
• Cancer Biology

Background:

• The tumor suppressor p53 regulates target genes via transcriptional activation or silencing.
• The mechanism by which p53 represses gene expression, particularly regarding DNA binding requirements, remains unclear.

Purpose of the Study:

• To investigate whether the human BKB1R gene is a target of p53-mediated repression.
• To elucidate the mechanism of p53's repressive function on the BKB1R gene.

Main Methods:

• Transient transfection assays using luciferase reporter constructs driven by the BKB1R promoter in SV40-transformed IMR90 cells.
• Dose-dependency studies of p53 expression on reporter activity.
• Analysis of promoter activity following etoposide-induced p53 expression.
• Reporter assays with modified BKB1R promoter constructs lacking putative p53 binding sites and TATA-box.

Main Results:

• p53 expression significantly suppressed BKB1R promoter and minigene activity in a dose-dependent manner.
• p53 reduced both basal and induced BKB1R promoter activity, abolishing inducibility.
• Etoposide-induced p53 also inhibited BKB1R promoter activity and inducibility.
• p53-mediated suppression of BKB1R was observed even when the putative p53 binding site and TATA-box were replaced, indicating independence from these elements.

Conclusions:

• The human BKB1R gene is a novel target gene repressed by p53.
• p53 suppresses BKB1R gene expression through a mechanism independent of direct DNA binding to its consensus sequence or interaction with the TATA-box.
• p53 does not appear to mediate BKB1R repression via interaction with c-Jun.