Induction of APOBEC3-mediated genomic damage in urothelium implicates BK polyomavirus (BKPyV) as a hit-and-run driver for bladder cancer

Simon C Baker,Manikandan Periyasamy,Katie T Skinner,Simak Ali,Andrew S Mason,Andrew Macdonald,Raphael G Slip,Reuben S Harris,Jennifer Southgate,Omar Masood,Tim R Fenton

doi:10.1038/s41388-022-02235-8

Abstract

Limited understanding of bladder cancer aetiopathology hampers progress in reducing incidence. Mutational signatures show the anti-viral apolipoprotein B mRNA editing enzyme catalytic polypeptide (APOBEC) enzymes are responsible for the preponderance of mutations in bladder tumour genomes, but no causative viral agent has been identified. BK polyomavirus (BKPyV) is a common childhood infection that remains latent in the adult kidney, where reactivation leads to viruria. This study provides missing mechanistic evidence linking reactivated BKPyV-infection to bladder cancer risk. We used a mitotically-quiescent, functionally-differentiated model of normal human urothelium to examine BKPyV-infection. BKPyV-infection led to significantly elevated APOBEC3A and APOBEC3B protein, increased deaminase activity and greater numbers of apurinic/apyrimidinic sites in the host urothelial genome. BKPyV Large T antigen (LT-Ag) stimulated re-entry from G0 into the cell cycle through inhibition of retinoblastoma protein and activation of EZH2, E2F1 and FOXM1, with cells arresting in G2. The single-stranded DNA displacement loops formed in urothelial cells during BKPyV-infection interacted with LT-Ag to provide a substrate for APOBEC3-activity. Addition of interferon gamma (IFNγ) to infected urothelium suppressed expression of the viral genome. These results support reactivated BKPyV infections in adults as a risk factor for bladder cancer in immune-insufficient populations.

Highlights

Urothelial cancer has a complex natural history with an indolent, frequently recurrent and unpredictably progressive disease path, which converges with a more aggressive route taken by malignancies that can present at advanced muscleinvasive and even disseminated stages
Studies of bladder tumour genomes have identified mutational signatures associated with the anti-viral apolipoprotein B mRNA editing enzyme catalytic polypeptide (APOBEC) family of cytosine deaminase enzymes in up to 93% of cases [3]
All genes of the BK polyomavirus (BKPyV) genome were expressed at 14 days-post-infection, with Agnoprotein the most and Large T antigen (LT-Ag) the least expressed transcripts (Fig. 2a with genome map as Fig. 2b)

Summary

Introduction

Urothelial (bladder) cancer has a complex natural history with an indolent, frequently recurrent and unpredictably progressive disease path, which converges with a more aggressive route taken by malignancies that can present at advanced muscleinvasive and even disseminated stages. Smoking is a well-established risk factor for bladder cancer (BLCA), the mutational signatures of bladder tumours show only a minor proportion of the G > T transversions characteristic of DNA damage caused directly by smoke-derived carcinogens [1, 2]. PyV are ubiquitous childhood infections, with 70–80% seroprevalence by adulthood [4] They are largely asymptomatic in the immuno-competent, but may remain latent in the adult kidney [5]. The only published study of BLCA risk (n = 3782), found a higher incidence of bladder tumours (15.8%) in the 133 patients with previous urine cytology evidence of BKPyV infection (OR3.4, p < 0.001) [7]

Methods

Results

Conclusion