Sirolimus and other mTOR inhibitors directly activate latent pathogenic human polyomavirus replication

Sirolimus and other mTOR inhibitors directly activate latent pathogenic human polyomavirus replication:

Abstract

Background

Human polyomaviruses can reactivate in transplant patients causing nephropathy, progressive multifocal leukoencephalopathy, Merkel cell carcinoma, pruritic rash or trichodysplasia spinulosa. Sirolimus and related mTOR inhibitors are transplant immunosuppressants. It is unknown if they directly reactivate polyomavirus replication from latency beyond their general effects on immunosuppression.

Methods

In vitro expression and turnover of large T (LT) proteins from BK, JC, Merkel cell, HPyV7 and trichodysplasia spinulosa polyomaviruses after drug treatment were determined by immunoblotting, proximity ligation, replicon DNA replication and whole virus immunofluorescence assays.

Results

mTOR inhibition increased LT protein expression for all 5 pathogenic polyomaviruses tested. This correlated with LT stabilization, decrease in the Skp2 E3 ligase targeting these LT proteins for degradation, as well as increase in virus replication for JCV, MCV, TSV and HPyV7. Treatment with sirolimus, but not the calcineurin inhibitor tacrolimus, at levels routinely achieved in patients, resulted in a dose-dependent increase in viral DNA replication for BKV, MCV and HPyV7.

Conclusions

mTOR inhibitors, at therapeutic levels, directly activate polyomavirus replication through a Skp2-dependent mechanism, revealing a proteostatic latency mechanism common to polyomaviruses. Modifying existing drug regimens for transplant patients with polyomavirus-associated diseases may reduce symptomatic polyomavirus replication while maintaining allograft-sparing immune suppression. immunosuppression.