Gain-of-Function Activity of Mutant p53 in Lung Cancer through Up-Regulation of Receptor Protein Tyrosine Kinase Axl

Abstract

Abstractp53 mutations are present in up to 70% of lung cancer. Cancer cells with p53 mutations, in general, grow more aggressively than those with wildtype p53 or no p53. Expression of tumor-derived mutant p53 in cells leads to up-regulated expression of genes that may affect cell growth and oncogenesis. In our study of this aggressive phenotype, we have investigated the receptor protein tyrosine kinase Axl, which is up-regulated by p53 mutants at both RNA and protein levels in H1299 lung cancer cells expressing mutants p53-R175H, -R273H, and -D281G. Knockdown of endogenous mutant p53 levels in human lung cancer cells H1048 (p53-R273C) and H1437 (p53-R267P) led to a reduction in the level of Axl as well. This effect on Axl expression is refractory to the mutations at positions 22 and 23 of p53, suggesting that p53's transactivation domain may not play a critical role in the up-regulation of Axl gene expression. Chromatin immunoprecipitation (ChIP) assays carried out with acetylated histone antibodies demonstrated induced histone acetylation on the Axl promoter region by mutant p53. Direct mutant p53 nucleation on the Axl promoter was demonstrated by ChIP assays using antibodies against p53. The Axl promoter has a p53/p63 binding site, which however is not required for mutant p53-mediated transactivation. Knockdown of Axl by Axl-specific RNAi caused a reduction of gain-of-function (GOF) activities, reducing the cell growth rate and motility rate in lung cancer cells expressing mutant p53. This indicates that for lung cancer cell lines with mutant p53, GOF activities are mediated in part through Axl.

Nondisruptive p53 Mutations Are Associated with Shorter Survival in Patients with Advanced Non–Small Cell Lung Cancer

“…Experimental evidence shows that many nondisruptive mutations, rather than causing simple loss of function of wt p53, induce GOF activities that can be exerted through direct transcriptional regulation or through inactivation of p63/p73 (12). These GOF activities are dominant over the TP53-wt allele and lead to increased tumorigenicity, growth rate, motility, metastasis and invasiveness, and decreased chemosensitivity in cell models (43). However, these phenotypes do not always appear together and different p53 mutants have been demonstrated to have different, complex patterns of GOF.…”

“…Examples of these GOF activities are the downregulation of apoptotic (FAS) and cell-arrest (CDKN1A) genes and the upregulation of immortalizing (TERT), mitogenic (EGR1, MYC), stress-protective (HSPA1A), angiogenic (ANGPT1), or drug resistance (ABCB1, AXL) genes. Overexpression of the Axl tyrosinekinase receptor (43), associated with the epithelial-tomesenchimal transition, leads to resistance to tyrosinekinase inhibitors.…”

Mutant p53 Gain of Function and Chemoresistance: The Role of Mutant p53 in Response to Clinical Chemotherapy

“…For instance, mutp53 binds NF-Y target promoters and recruits p300, leading to histone acetylation and NF-Y target transcription. Likewise, mutp53 recruits p300 to the promoter of receptor protein tyrosine kinase Axl, elevating histone H4 and H3 acetylation to promote Axl expression [37]. Moreover, mutp53 recruits CBP to NF-κB2 promoter regions, promoting histone H4 acetylation to facilitate NF-κB2 expression [15].…”

Nedaplatin sensitization of cisplatin-resistant human non-small cell lung cancer cells

“…Lung cancer cells have been shown to possess a higher p53 mutation rate (70%); the mutation of the gene could result in abnormal expression of the p53 protein (17). The wild-type p53 protein is able to exert a range of anti-proliferative effects, including the induction of apoptosis and causing a marked increase in the sensitivity of these cells to DDP (18,19).…”