Abstract
Tylophorine-based compounds exert broad spectral, potent inhibition of coronaviruses. NF-κB activation is a common pro-inflammatory response of host cells to viral infection. The aims of this study were to (i) find an effective combination treatment for coronaviral infections through targeting of the virus per se and cellular NF-κB activity; and (ii) to study the underling mechanisms. We found that tylophorine-based compounds target the TGEV viral RNA and effectively inhibit TGEV replication. NF-κB inhibition also leads to anti-TGEV replication. NF-κB activation induced by TGEV infection was found to be associated with two convergent pathways, IKK-2_IκBα/p65 and JAK2 mediated p65 phosphorylation, in swine testicular cells. JAK2 inhibition either by CYT387 (a JAK family inhibitor) or by silencing JAK2-expression revealed a dominant JAK2 mediated p65 phosphorylation pathway for NF-κB activation and resulted in NF-κB inhibition, which overrode the IκBα regulation via the IKK-2. Finally, tylophorine-based compounds work cooperatively with CYT387 to impart comprehensive anti-TGEV activities. The combination treatment, wherein a tylophorine compound targets TGEV and a JAK2 inhibitor blocks the alternative dominant NF-κB activation mediated by JAK2, is more effective and comprehensive than either one alone and constitutes a feasible approach for the treatment of SARS-CoV or MERS-CoV.
Highlights
Coronaviruses are animal viruses containing an enveloped, positive-sense, single-stranded RNA genome; and include the common cold human coronavirus (CoV)-229E & CoV-OC43, severe acute respiratory syndrome (SARS) CoV, Middle East respiratory syndrome (MERS) CoV, porcine transmissible gastroenteritis virus (TGEV), and murine hepatitis virus (MHV) etc[1,2,3]
Using 5-ethynyl uridine (EU) labelled newly synthesized RNA, we clearly demonstrated that tylophorine compounds, either tylophorine or DBQ 33b, inhibited the nascent viral RNA synthesis and blocked the colocalization of viral nascent RNA with either N protein (Fig. 1D-a) or RNA-dependent RNA polymerase (RdRP) (Fig. 1D-b) around nuclei
Human coronaviruses constitute a grave threat to public health, a situation exemplified by the outbreaks of SARS-CoV in 2003 and MERS-CoV in 2012
Summary
Coronaviruses are animal viruses containing an enveloped, positive-sense, single-stranded RNA genome; and include the common cold human coronavirus (CoV)-229E & CoV-OC43, severe acute respiratory syndrome (SARS) CoV, Middle East respiratory syndrome (MERS) CoV, porcine transmissible gastroenteritis virus (TGEV), and murine hepatitis virus (MHV) etc[1,2,3]. Many small chemical molecules targeting either viral entry or the intracellular viral life cycle were reported to impart anti-coronavirus activity[2, 9, 10]. Despite these advances, SARS-CoV and MERS-CoV remain untreatable diseases for which novel therapies are sought. Tylophorine based compounds, whether isolated from plants, e.g. Asclepiadaceae and Moraceae or chemically synthesized, exert potent anti-coronaviral activities against a variety of coronaviruses including SARS-CoV, MHV, and TGEV11, 12, but both the underlying mechanism(s) of this inhibitory effect and the target are unknown. We report: (1) tylophorine-based compounds exert potent anti-TGEV replication by directly targeting the viral RNA/ribonucleoprotein (RNP) complex for viral replication/synthesis; (2) NF-κB inhibition leads to anti-TGEV replication; (3) A combination treatment consisting of both a tylophorine compound and an NF-κB inhibitor acts additively or synergically to more effectively and comprehensively inhibit TGEV replication than either (1) or (2) alone
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