Tumor-Derived p53 Mutants Induce NF-κB2 Gene Expression

Abstract

Overexpression of mutant p53 is a common theme in tumors, suggesting a selective pressure for p53 mutation in cancer development and progression. To determine how mutant p53 expression may lead to survival advantage in human cancer cells, we generated stable cell lines expressing p53 mutants p53-R175H, -R273H, and -D281G by use of p53-null human H1299 (lung carcinoma) cells. Compared to vector-transfected cells, H1299 cells expressing mutant p53 showed a survival advantage when treated with etoposide, a common chemotherapeutic agent; however, cells expressing the transactivation-deficient triple mutant p53-D281G (L22Q/W23S) had significantly lower resistance to etoposide. Gene expression profiling of cells expressing transcriptionally active mutant p53 proteins revealed the striking pattern that all three p53 mutants induced expression of approximately 100 genes involved in cell growth, survival, and adhesion. The gene NF-B2 is a prominent member of this group, whose overexpression in H1299 cells also leads to chemoresistance. Treatment of H1299 cells expressing p53-R175H with small interfering RNA specific for NF-B2 made these cells more sensitive to etoposide. We have also observed activation of the NF-B2 pathway in mutant p53-expressing cells. Thus, one possible pathway through which mutants of p53 may induce loss of drug sensitivity is via the NF-B2 pathway.Mutation in the p53 tumor suppressor gene is a common event in human cancer (6,36,40,43,44,65,71,72). Unlike what is seen for other tumor suppressors, in the majority of human carcinomas with p53 mutations, a protein with one amino acid substitution is overexpressed, suggesting the existence of a selection pressure for maintaining expression of the mutant protein (6,36,40,43,44,65,71,72). This also is perhaps indicative of an active role played by p53 mutants in oncogenesis and follows the gain-of-function hypothesis, which predicts not only that mutations in the p53 gene destroy the tumor suppressor function of the wild-type (WT) protein but that the mutant proteins may also gain oncogenic functions. The gain-of-function hypothesis also predicts that tumors with mutant p53 proteins may be more aggressive or that patients with tumors harboring mutant p53 have poorer prognoses than patients with tumors lacking the p53 protein. This has been found to be true for various types of cancers (10,28,29,81,82,88).WT p53 is a sequence-specific transactivator of promoters containing p53-binding sites. Elevated levels of WT p53 in response to cellular stress situations, such as DNA damage, can lead to apoptosis or induce cell cycle arrest (26,53,60,68,84,89,91) by inducing expression of genes involved in various aspects of cellular growth regulation (21,26,27,49,50,53,60,63,68,84,89,91). A mutation in one allele of p53 generates a stable mutant protein with compromised tumor suppressor function. However, there is compelling evidence to suggest that apart from loss of growth suppressor function, p53 mutants can confer oncogenic properties even in the absence of WT p53...

Transcription regulation by mutant p53

“…This gene encodes the p100/p52 subunit of NF-kB. In line with this finding, overexpression of mutp53 was shown to increase NF-kB activity and protect cells against chemotherapy-induced death (Scian et al, 2005). More recently, it was found that mutp53 can also augment and prolong the activation of NF-kB by tumor necrosis factor alpha (TNF-a), in this case acting via the canonical p50-p65 NF-kB complex (L Weisz and A Damalas, unpublished).…”

Mutant p53 gain of function can be at the root of dedifferentiation of human osteosarcoma MG63 cells into 3AB-OS cancer stem cells

“…It is known that TP53 mutations occur in almost every type of cancer and often mutant p53 proteins (mutp53) express gain of function (GOF), which can enhance the ability of cancer cells to invade and metastasize, confer resistance to chemotherapies, promote genomic instability and drive multinucleation [18][19][20][21][22][23][24][25][26][27]. Recently, evidence linking p53 loss to stem-like phenotype in cancer has been reported [28]; however, how p53 contributes to acquisition of "stemness" at the molecular level and whether stem-like cells confer survival advantages to propagate the tumor remains to be resolved.…”

Sarcomas in TP53 germline mutation carriers

“…In addition, some mutations can cause ''gain of function'' whereby mutant p53 protein assumes an oncogenic role and promotes tumor development. [16][17][18] To date, a total of 532 families or individuals with germline TP53 mutations have been reported in the peerreviewed literature. 19 Information on these mutations, on tumor pathologies and localization, and on age of diagnosis in mutation carriers is compiled into the TP53 database maintained at the International Agency for Research on Cancer (IARC).…”