Natural cardenolides suppress coronaviral replication by downregulating JAK1 via a Na(+)/K(+)-ATPase independent proteolysis

An unprecedented biological function of natural cardenolides independent of their membrane target Na(+)/K(+)-ATPase is disclosed. Previously, we reported that cardenolides impart anti-transmissible gastroenteritis coronavirus (anti-TGEV) activity through the targeting of Na(+)/K(+)-ATPase and its associated PI3K_PDK1_RSK2 signaling. Swine testis cells with Na(+)/K(+)-ATPase α1 knocked down exhibited decreased susceptibility to TGEV infectivity and attenuated PI3K_PDK1_RSK2 signaling. Herein, we further explored a Na(+)/K(+)-ATPase-independent signaling axis induced by natural cardenolides that also afforded significant anti-coronaviral activity for porcine TGEV and human HCoV-OC43. Using pharmacological inhibition and gene silencing techniques, we found that this anti-TGEV or anti-HCoV-OC43 activity was caused by JAK1 proteolysis and mediated through upstream activation of Ndfip1/2 and its effector NEDD4. This study provides novel insights into the pharmacological effects of natural cardenolides, and is expected to inform their future development as antiviral agents.