Large yellow croaker(Larimichthys crocea)mitofusin 2 inhibits type I IFN responses by degrading MAVS via enhanced K48‑linked ubiquitination

In mammals,mitofusin 2(MFN2)is involved in mitochondrial fusion,and suppresses the virus-induced RIG-I-like receptor(RLR)signaling pathway.However,little is known about the function of MFN2 in non-mammalian species.In the present study,we cloned an MFN2 ortholog(LcMFN2)in large yellow croaker(Larimichthys crocea).Phylogenetic analysis showed that MFN2 emerged after the divergence of amphioxus and vertebrates.The protein sequences of MFN2 were well conserved from fsh to mammals.LcMFN2 was expressed in all the tissues/organs examined at diferent levels,and its expression was upregulated in response to poly(I:C)stimulation.Overexpression of LcMFN2 inhibited MAVS-induced type I interferon(IFN)promoter activation and antiviral gene expression.In contrast,knockdown of endogenous LcMFN2 enhanced poly(I:C)induced production of type I IFNs.Additionally,LcMFN2 enhanced K48-linked polyubiquitination of MAVS,promoting its degradation.Also,overexpression of LcMFN2 impaired the cellular antiviral response,as evidenced by the increased expression of viral genes and more severe cytopathic efects(CPE)in cells infected with spring viremia of carp virus(SVCV).These results indicated that LcMFN2 inhibited type I IFN response by degrading MAVS,suggesting its negative regulatory role in cellular antiviral response.Therefore,our study sheds a new light on the regulatory mechanisms of the cellular antiviral response in teleosts.

High-density lipoprotein regulates angiogenesis by long non-coding RNA HDRACA

Normal high-density lipoprotein(nHDL)can induce angiogenesis in healthy individuals.However,HDL from patients with coronary artery disease undergoes various modifications,becomes dysfunctional(dHDL),and loses its ability to promote angiogenesis.Here,we identified a long non-coding RNA,HDRACA,that is involved in the regulation of angiogenesis by HDL.In this study,we showed that nHDL downregulates the expression of HDRACA in endothelial cells by activating WW domain-containing E3 ubiquitin protein ligase 2,which catalyzes the ubiquitination and subsequent degradation of its transcription factor,Kruppel-like factor 5,via sphingosine 1-phosphate(S1P)receptor 1.In contrast,dHDL with lower levels of S1P than nHDL were much less effective in decreasing the expression of HDRACA.HDRACA was able to bind to Ras-interacting protein 1(RAIN)to hinder the interaction between RAIN and vigilin,which led to an increase in the binding between the vigilin protein and proliferating cell nuclear antigen(PCNA)mRNA,resulting in a decrease in the expression of PCNA and inhibition of angiogenesis.The expression of human HDRACA in a hindlimb ischemia mouse model inhibited the recovery of angiogenesis.Taken together,these findings suggest that HDRACA is involved in the HDL regulation of angiogenesis,which nHDL inhibits the expression of HDRACA to induce angiogenesis,and that dHDL is much less effective in inhibiting HDRACA expression,which provides an explanation for the decreased ability of dHDL to stimulate angiogenesis.