JAK1 depletion or downregulation was previously reported to account for coronavirus inhibition. Here, we found that
AG1024, an IR (
insulin receptor) and IGF-1R (
insulin-like growth factor 1 receptor) inhibitor, diminishes JAK1
protein levels and exerts anti-coronaviral activities with EC50 values of 5.2 ± 0.3 μM against transmissible
gastroenteritis coronavirus (TGEV) and 4.3 ± 0.3 μM against
human flu coronavirus OC43. However, although the IR and IGF-1R signaling pathways are activated by
insulin or
IGF-1 in swine testis cells, they are not triggered upon TGEV
infection.
AG1024, therefore, inhibits coronaviral replication and downregulates JAK1
protein levels independently of IR and IGF-1R. Moreover, JAK1 proteolysis caused by
AG1024 was found through activation of upstream Ndfip1/2 and its effector NEDD4-like
E3 ligase Itch. In addition,
ouabain, which was reported to mediate JAK1 proteolysis causing anti-coronaviral activity by activation of Ndfip1/2 and NEDD4
E3 ligase, additively inhibited anti-coronaviral activity and JAK1 diminishment in combination with
AG1024. This study provides novel insights into the pharmacological effects of
AG1024 and Itch
E3 ligase mediated JAK1 proteolysis and identified Ndfip1/2 as a cognate effector for JAK1 proteolysis via the diversified E3
ligases NEDD4 and NEDD4-like Itch. These findings are expected to provide valued information for the future development of anti-viral agents.