Sirolimus and Other Mechanistic Target of Rapamycin Inhibitors Directly Activate Latent Pathogenic Human Polyomavirus...

Area of Science:

• Virology
• Immunology
• Pharmacology

Background:

• Human polyomaviruses can cause serious diseases in transplant patients, including nephropathy and progressive multifocal leukoencephalopathy.
• The immunosuppressive drugs sirolimus and mechanistic target of rapamycin (mTOR) inhibitors are commonly used in transplant recipients.
• It remains unclear whether these mTOR inhibitors directly trigger polyomavirus replication beyond their general immunosuppressive effects.

Purpose of the Study:

• To investigate whether mechanistic target of rapamycin (mTOR) inhibitors directly influence the replication of human polyomaviruses.
• To elucidate the molecular mechanisms underlying any observed direct effects of mTOR inhibitors on polyomavirus replication.

Main Methods:

• In vitro assessment of large T (LT) protein expression and turnover for five pathogenic human polyomaviruses (BK virus, JC virus, Merkel cell polyomavirus, HPyV7, TSV) following drug treatment.
• Utilized immunoblotting, proximity ligation assays, replicon DNA replication assays, and whole virus immunofluorescence assays to analyze viral protein activity and replication.

Main Results:

• mTOR inhibition significantly increased LT protein expression across all five tested polyomaviruses.
• This increase correlated with LT protein stabilization, reduced degradation mediated by the Skp2 E3 ligase, and enhanced viral replication for JC virus, MCV, TSV, and HPyV7.
• Sirolimus, at therapeutic concentrations, demonstrated a dose-dependent increase in viral DNA replication for BK virus, MCV, and HPyV7, unlike tacrolimus.

Conclusions:

• mTOR inhibitors directly activate polyomavirus replication at therapeutic levels via a Skp2-dependent mechanism, revealing a common proteostatic latency pathway for polyomaviruses.
• Findings suggest potential for modifying immunosuppressive drug regimens in transplant patients to mitigate symptomatic polyomavirus replication while preserving essential immunosuppression for allograft survival.