IADR Abstract Archives
CXCL5 Activation by Mutant p53 in Head and Neck Cancer
Objectives: Oncogenic gain-of-function (GOF) p53 mutants can actively drive tumor progression, resulting in more aggressive growth, angiogenesis and metastatic spread, and a worse prognosis than in cases where wild-type p53 is merely absent. Inflammation is a key factor in tumorigenesis and is driven, at least in part, by chemokines and their receptors that not only serve to recruit inflammatory cells to the tumor but also stimulate tumor cell growth, motility and metastasis. Previous studies from our laboratory have reported elevated levels of chemokines CXCL5 and CXCL8 in head and neck cancer, and that expression of these is promoted by GOF p53 mutants. The purpose of this study was to investigate possible mechanisms leading to deregulated expression of CXCL5 by GOF p53.
Methods: Head and neck cancer cells with low endogenous CXCL5 expression and functionally null for p53 were used as a model cell line. Cells were engineered to express GOF mutant p53 or, alternatively, endogenous protein expression was reduced by RNA interference. CXCL5 expression was determined by quantitative PCR, western blot and ELISA assay. Binding of mutant p53 and p63 to the CXCL5 promoter was determined by chromatin immunoprecipitation and quantitative PCR.
Results: CXCL5 expression was increased significantly in cells expressing GOF mutant p53 compared to control transfected cells. Additionally, siRNA-mediated knockdown of endogenous p63 also led to elevated levels of CXCL5. Co-immunoprecipitation experiments indicated that GOF p53 and p63 physically interacted in these cells. Chromatin immunoprecipitation data revealed nucleation of p63 on the CXCL5 promoter in the absence of GOF p53, but in the presence of GOF p53 no p63 binding was observed. Where GOF p53 was expressed, it was found to bind to the CXCL5 promoter region. Binding of both p63 and GOF p53 occurred upstream of the previously identified FOXM1 binding site in the CXCL5 promoter.
Conclusions: Increased expression of CXCL5 in head and neck cancer cells may be regulated by gain-of-function mutant p53, in part through a trans-dominant repression of p63, which appears to act as a negative regulator of CXCL5.
Methods: Head and neck cancer cells with low endogenous CXCL5 expression and functionally null for p53 were used as a model cell line. Cells were engineered to express GOF mutant p53 or, alternatively, endogenous protein expression was reduced by RNA interference. CXCL5 expression was determined by quantitative PCR, western blot and ELISA assay. Binding of mutant p53 and p63 to the CXCL5 promoter was determined by chromatin immunoprecipitation and quantitative PCR.
Results: CXCL5 expression was increased significantly in cells expressing GOF mutant p53 compared to control transfected cells. Additionally, siRNA-mediated knockdown of endogenous p63 also led to elevated levels of CXCL5. Co-immunoprecipitation experiments indicated that GOF p53 and p63 physically interacted in these cells. Chromatin immunoprecipitation data revealed nucleation of p63 on the CXCL5 promoter in the absence of GOF p53, but in the presence of GOF p53 no p63 binding was observed. Where GOF p53 was expressed, it was found to bind to the CXCL5 promoter region. Binding of both p63 and GOF p53 occurred upstream of the previously identified FOXM1 binding site in the CXCL5 promoter.
Conclusions: Increased expression of CXCL5 in head and neck cancer cells may be regulated by gain-of-function mutant p53, in part through a trans-dominant repression of p63, which appears to act as a negative regulator of CXCL5.