The presence of ∆133p53 and ∆40p53 in metastatic brain tumours: evidence for further enquiries

Abstract

Metastatic brain tumours are becoming more prevalent as individuals with primary cancers receive improved treatment and live longer. These brain tumours are difficult to treat and are often left undiagnosed. This study looked at determining if tumour protein 53 (p53) isoforms were expressed in brain metastases. An isoform investigated, ∆133p53, has been implicated in promoting tumour migration and in primary brain tumours was associated with treatment resistance and inflammatory characteristics including increased programmed death-ligand 1 (PD-L1) expression. We hypothesised that ∆133p53 was elevated in the metastatic brain tumour cells, coupled with increased PD-L1 expression. Expression of ∆133p53 was determined in tissue sections of brain tumour metastases (n = 24) using RNAscope in situ hybridisation assays. The presence of other p53 isoforms was investigated in brain tumour metastases (n = 21) with an analysis of six isoforms using quantitative real-time PCR. PD-L1 expression was assessed by using immunohistochemistry.

Analysis of RNAscope slides show that ∆133p53 was expressed in tumour cells of brain metastases, we could identify ∆133p53 staining in 14 of the 24 tumours analysed (4 breast, 4 colorectal, 4 lung, and 2 melanoma). All of the brain metastases expressed each of the p53 isoforms measured (∆40p53, ∆133p53, p53α, and p53β). Interestingly, the highest expressed isoforms were ∆40p53 and p53α, and not ∆133p53 and p53β. This was true for all tumour groups, except breast cancer where the expression of ∆40p53, ∆133p53, p53α, and p53β were relatively similar. Pairwise-Spearman’s correlation analyses of relative mRNA expression indicate that ∆40p53α (ρ = 0.9, p < 0.0001) ∆133p53β (ρ = 0.88, p < 0.0001) were the most likely combination of isoforms present. Only 6 of the 25 tumours analysed for PDL1 contained PDL1-positive cells. Results thus far indicate that p53 isoforms are present in brain tumour metastases. The findings in this study provide a basis for future investigations of p53 isoforms in brain metastases. Future work could investigate ∆33p53β in breast metastases in a larger cohort. Other p53 isoforms, such as ∆40p53α should also be investigated to determine the role that p53 isoforms have in brain tumour metastasis.