Insights into SARS-CoV-2 replication control via targeting the host hijacking function of NSP12.

Nonstructural protein 12 (NSP12), the RNA-dependent RNA polymerase (RdRp) of SARS-CoV-2, serves as the catalytic core of the viral replication-transcription complex and is pivotal for viral RNA synthesis. Given its essential role, SARS-CoV-2 must precisely regulate intracellular NSP12 levels to support efficient viral replication. However, the mechanisms governing its stability remain poorly understood. Here, we reveal a previously unrecognized viral strategy in which NSP12 hijacks the host chaperone Hsc70 to modulate its own stability. Mechanistically, Hsc70 plays a dual role: mediating NSP12 degradation via chaperone-mediated autophagy (CMA) while also promoting its accumulation. The dynamic balance between these opposing functions determines NSP12 fate. NSP12 can evade CMA-mediated degradation by binding Hsc70 with higher affinity. This disrupts the Hsc70-LAMP2a interaction and shifts Hsc70's role toward primarily facilitating NSP12 accumulation, thereby enhancing viral replication. We identified Hlyc41 as a potential antiviral agent that disrupts this hijacking mechanism. Hlyc41 competes with NSP12 for binding to the F428 residue of Hsc70, thereby promoting NSP12 degradation and suppressing viral replication. These findings reveal a novel host hijacking mechanism that regulates NSP12 levels and support a promising therapeutic strategy targeting this process.