Chaperones and Ubiquitin Ligases Balance Mutant p53 Protein Stability in Esophageal and Other Digestive Cancers

Abstract

The incidence of esophageal adenocarcinoma (EAC) and other gastrointestinal (GI) cancers have risen dramatically, thus defining the oncogenic drivers to develop effective therapies are necessary. Patients with Barrett's Esophagus (BE), have an elevated risk of developing EAC. Around 70%-80% of BE cases that progress to dysplasia and cancer have detectable TP53 mutations. Similarly, in other GI cancers higher rates of TP53 mutation are reported, which provide a significant survival advantage to dysplastic/cancer cells. Targeting molecular chaperones that mediate mutant p53 stability may effectively induce mutant p53 degradation and improve cancer outcomes. Statins can achieve this via disrupting the interaction between mutant p53 and the chaperone DNAJA1, promoting CHIP-mediated degradation of mutant p53, and statins are reported to significantly reduce the risk of BE progression to EAC. However, statins demonstrated sub-optimal efficacy depending on cancer types and TP53 mutation specificity. Besides the well-established role of MDM2 in p53 stability, we reported that individual isoforms of the E3 ubiquitin ligase GRAIL (RNF128) are critical, tissue-specific regulators of mutant p53 stability in BE progression to EAC, and targeting the interaction of mutant p53 with these isoforms may help mitigate EAC development. In this review, we discuss the critical ubiquitin-proteasome and chaperone regulation of mutant p53 stability in EAC and other GI cancers with future insights as to how to affect mutant p53 stability, further noting how the precise p53 mutation may influence the efficacy of treatment strategies and identifying necessary directions for further research in this field.

Keywords: HSP; Heat Shock Protein; RNF128/GRAIL; UPS; Ubiquitin Proteasome System; p53.

Figure 1

Key ubiquitin ligases (E3) and chaperones involved in tilting the balance toward increased stabilization of mutant p53 (p53∗) to promote BE progression to EAC. Critical ligases include MDM2, CHIP, β-TrCP1, WWP1, RNF128, etc, and various HSP family members including Hsp40, Hsp70, and Hsp90 are the chaperones involved those determine the p53∗ protein levels tilting the balance toward increased stability during BE progression.

Figure 2

Common TP53 mutations in BE with frequency data across common GI cancers. (Upper panel) Using our extended progression-related cohort of dysplasia-enriched BE tissues (n = 181) from HGD/EAC resection patients, we present frequencies for the most commonly targeted amino acids across BE dysplasia groups, based on histological assessment: BE tissue with a low-risk of progression based on absence or low levels of dysplasia (<50% of BE tissue as LGD, with regional no evidence of HGD); high proportion LGD (50% or greater, with no evidence of HGD); regions with <50% HGD; regions with more than 50% HGD and EAC. Numbers given on the left represent the number of cases with TP53 mutations, used as a base line for % AA targeted mutations, while numbers of the right show the overall TP53 mutation percentage, with total number of samples for each group (in brackets) used as a baseline. (Lower panel) Comparative mutation rates for common GI cancers, using the International Agency for Research on Cancer (IARC) TP53 database of curated TP53 mutations associated with human cancers either from peer-reviewed literature or curated from other genomic databases. Baseline totals (shown on the left) represent the number of records from each cancer group with p53 mutations reported with designated amino acid localizations. The rightmost columns in the lower section shows the overall percentage of TP53 mutations for each cancer type, drawn from The Cancer Genome Atlas (TCGA)–based cohorts (from cBioportal interface) used in comparable GI cancer–type studies, with the total number of samples for each cancer type (shown in brackets) used as a baseline. Color coding key on the far right is a categorical visual guide to the quoted amino acid specific percentages, with frequencies rare (>2%) to common (10%–20%) shaded from light to dark. NDBE, nondysplastic Barrett’s esophagous; SCC, squamous cell carcinoma.

Figure 3

Mechanisms that regulate the balance between mutant p53 (p53∗) degradation and stabilization. Misfolded/unfolded mutant p53 (p53∗) may be recognized by ubiquitin ligases or molecular chaperones. (Panel A, i-iii) Ubiquitin ligases including CHIP, MDM2 and RNF128 Iso2 are able to efficiently polyubiquitinate p53∗, leading to its subsequent proteasomal degradation. (Panel A, iv) The ubiquitin ligase β-TrCP1 may also indirectly contribute to p53∗ degradation, through promoting degradation of RNF128 Iso1. Molecular chaperones compete with the action of these ubiquitin ligases on p53∗ to instead promote stabilization. (Panel B, i-ii) Molecular chaperone activity drives p53∗ refolding and exhibits a protective effect against the activity of ubiquitin ligases such as CHIP and MDM2. p53∗ may be recognized by the molecular co-chaperone Hsp40, which is known to coordinate with Hsp70. Statins have been shown to disrupt the Hsp40 (DNAJA1)-p53∗ interaction, in turn promoting CHIP-mediated degradation. p53∗ is also observed in complexes with both HSP70 and HSP90 machinery; this may be counteracted by Hsp90 inhibitors. The refolding activity of these chaperones help p53∗ reach a more stable conformation that is less vulnerable to degradation. The ability of p53∗ to reach this stable conformation varies based on the exact mutation and its effect on the protein’s properties and structure. Mutants that are found predominantly folded in the cell reach this final conformation with more ease. The folding intermediates of other p53 mutants, most often found in an unfolded conformation in cells, are more likely to instead participate in aggregation, forming pseudo-aggregates with chaperones and other proteins such as p73 that resist degradation. The addition of MDM2 to these complexes promotes the formation of stable amyloid-like fibrils. (Panel B, iii) Additionally, RNF128 Iso1 promotes p53∗ stability through mitigating RNF128 Iso2-mediated p53∗ ubiquitination.