Repression of beta interferon gene expression in virus-infected cells is correlated with a poly(A) tail elongation

cGAS-ISG15-RAGE axis reprogram necroptotic microenvironment and promote lymphatic metastasis in head and neck cancer

BACKGROUND

Cancer cells frequently evolve necroptotic resistance to overcome various survival stress during tumorigenesis. However, we have previously showed that necroptosis is widespread in head and neck squamous cell carcinoma (HNSCC) and contributes to tumor progression and poor survival via DAMPs-induced migration and invasiveness in peri-necroptotic tumor cells. This implicated an alternative strategy that cancers cope with necroptotic stress by reprogramming a pro-invasive necroptotic microenvironment (NME). Here, we aim to decipher how necroptotic cells shape the NME and affect HNSCC progression.

METHODS

Both our pre-established cellular necroptotic model and newly established Dox-induce intratumoral necroptosis model were used to investigate how necroptosis affect HNSCC progression. Transcriptomic alterations in peri-necroptotic tumor cells were analyzed by RNA-seq and validated in the NME in mice and patients' samples. The differential DAMPs compositon among apopotosis. Necrosis, and necroptosis were analyzed by label-free proteomic technique, and the necroptosis-specific DAMPs were then identified and validated. The potential receptor for ISG15 were simulated using molecular docking and further validated by in vitro assays. Then the ISG15-RAGE axis was blocked by either knockdown of necroptotic-ISG15 release and RAGE inhibitor FPS-ZM1, and the impact on tumor progression were tested. Last, we further tested our findings in a HNSCC-patients cohort.

RESULTS

Necroptosis played a crucial role in driving tumor-cell invasiveness and lymphatic metastasis via tumor-type dependent DAMPs-releasing. Mechanistically, necroptotic DAMPs induced peri-necroptotic EMT via NF-κB and STAT3 signaling. Furthermore, intrinsic orchestration between necroptotic and cGAS-STING signaling resulted in producing a group of interferon stimulated genes (ISGs) as HNSCC-dependent necroptotic DAMPs. Among them, ISG15 played an essential role in reprogramming the NME. We then identified RAGE as a novel receptor for extracellular ISG15. Either blockage of ISG15 release or ISG15-RAGE interaction dramatically impeded necroptosis-driven EMT and lymphatic metastasis in HNSCC. Lastly, clinicopathological analysis showed high ISG15 expression in NME. Extensive necroptosis and high tumor-cell RAGE expression correlated with tumor progression and poor survival of HNSCC patients.

CONCLUSIONS

Our data revealed a previously unknown cGAS-ISG15-RAGE dependent reprogramming of the necroptotic microenvironment which converts the necroptotic stress into invasive force to foster HNSCC-cell dissemination. By demonstrating the programmatic production of ISG15 via necroptosis-cGAS orchestration and its downstream signaling through RAGE, we shed light on the unique role of ISG15 in HNSCC progression. Targeting such machineries may hold therapeutic potential for restoring intratumoral survival stress and preventing lymphatic metastasis in HNSCC.

Post-transcriptional control of type I interferon induction by porcine reproductive and respiratory syndrome virus in its natural host cells

Porcine reproductive and respiratory syndrome virus (PRRSV) is not only a poor inducer of type I interferon but also inhibits the efficient induction of type I interferon by porcine transmissible gastroenteritis virus (TGEV) and synthetic dsRNA molecules, Poly I:C. However, the mechanistic basis by which PRRSV interferes with the induction of type I interferon in its natural host cells remains less well defined. The purposes of this review are to summarize the key findings in supporting the post-transcriptional control of type I interferon in its natural host cells and to propose the possible role of translational control in the regulation of type I interferon induction by PRRSV.

The leader proteinase of foot-and-mouth disease virus inhibits the induction of beta interferon mRNA and blocks the host innate immune response

We have previously shown that the leader proteinase (L(pro)) of foot-and-mouth disease virus (FMDV) blocks cap-dependent mRNA translation and that a genetically engineered FMDV lacking the leader proteinase coding region (A12-LLV2) is attenuated in cell culture and susceptible animals. The attenuated phenotype apparently is a consequence of the inability of A12-LLV2 to block the expression of type I interferon (IFN-alpha/beta) protein, resulting in IFN-induced inhibition of FMDV replication. Here we show that in addition to preventing IFN-alpha/beta protein synthesis, L(pro) reduces the level of immediate-early induction of IFN-beta mRNA and IFN-stimulated gene products such as double-stranded RNA-dependent protein kinase R (PKR), 2',5'-oligoadenylate synthetase, and Mx1 mRNAs in swine cells. Down-regulation of cellular PKR by RNA interference did not affect wild-type virus yield but resulted in a higher yield of A12-LLV2, indicating a direct role of PKR in controlling FMDV replication in the natural host. The observation that L(pro) controls the transcription of genes involved in innate immunity reveals a novel role of this protein in antagonizing the cellular response to viral infection.

Vertebrate GLD2 poly(A) polymerases in the germline and the brain

Cytoplasmic polyadenylation is important in the control of mRNA stability and translation, and for early animal development and synaptic plasticity. Here, we focus on vertebrate poly(A) polymerases that are members of the recently described GLD2 family. We identify and characterize two closely related GLD2 proteins in Xenopus oocytes, and show that they possess PAP activity in vivo and in vitro and that they bind known polyadenylation factors and mRNAs known to receive poly(A) during development. We propose that at least two distinct polyadenylation complexes exist in Xenopus oocytes, one of which contains GLD2; the other, maskin and Pumilio. GLD2 protein interacts with the polyadenylation factor, CPEB, in a conserved manner. mRNAs that encode GLD2 in mammals are expressed in many tissues. In the brain, mouse, and human GLD2 mRNAs are abundant in anatomical regions necessary for long-term cognitive and emotional learning. In the hippocampus, mouse GLD2 mRNA colocalizes with CPEB1 and Pumilio1 mRNAs, both of which are likely involved in synaptic plasticity. We suggest that mammalian GLD2 poly(A) polymerases are important in synaptic translation, and in polyadenylation throughout the soma.

Suppression of the induction of alpha, beta, and lambda interferons by the NS1 and NS2 proteins of human respiratory syncytial virus in human epithelial cells and macrophages [corrected]

Wild-type human respiratory syncytial virus (HRSV) is a poor inducer of alpha/beta interferons (IFN-alpha/beta). However, recombinant HRSV lacking the NS1 and NS2 genes (Delta NS1/2) induced high levels of IFN-alpha and -beta in human pulmonary epithelial cells (A549) as well as in macrophages derived from primary human peripheral blood monocytes. Results with NS1 and NS2 single- and double-gene-deletion viruses indicated that the two proteins function independently as well as coordinately to achieve the full inhibitory effect, with NS1 having a greater independent role. The relative contributions of the individual NS proteins were the converse of that recently described for bovine RSV (J. F. Valarcher, J. Furze, S. Wyld, R. Cook, K. K. Conzelmann, and G. Taylor, J. Virol. 77:8426-8439, 2003). This pattern of inhibition by HRSV NS1 and NS2 also extended to the newly described antiviral cytokines IFN-lambda 1, -2 and -3.

Deadenylation of interferon-beta mRNA is mediated by both the AU-rich element in the 3'-untranslated region and an instability sequence in the coding region

Viral infection of fibroblastic and endothelial cells leads to the transient synthesis of interferon-beta (IFN-beta). The down-regulation of IFN-beta synthesis after infection results both from transcriptional repression of the IFN-beta gene and rapid degradation of mRNA. As with many cytokine mRNAs, IFN-beta mRNA contains an AU-rich element (ARE) in its 3'-untranslated region (UTR). AREs are known to mediate mRNA deadenylation and destabilization. Depending on the class of ARE, deadenylation was shown to occur through synchronous or asynchronous mechanisms. In this study, we analysed IFN-beta mRNA deadenylation in natural conditions of IFN-beta synthesis, e.g., after viral infection. We show that human IFN-beta mRNA follows an asynchronous deadenylation pathway typical of a mRNA containing a class II ARE. A deletion analysis of the IFN-beta natural transcript demonstrates that poly(A) shortening can be mediated by the ARE but also by a 32 nucleotide-sequence located in the coding region, that was identified previously as an instability determinant. In fact, these elements are able to act independently as both of them have to be removed to abrogate mRNA deadenylation. Our data also indicate that deadenylation occurs independently of mRNA translation. Moreover, we show that deadenylation of IFN-beta mRNA is not under the control of viral infection as IFN-beta mRNA derived from a constitutively expressed gene cassette is deadenylated in absence of viral infection. Finally, an unidentified nuclear event appears to be a prerequisite for IFN-beta mRNA deadenylation as IFN-beta mRNA introduced directly into the cytoplasm does not undergo deadenylation. In conclusion, our study demonstrates that IFN-beta mRNA poly(A) shortening is under the control of two cis-acting elements recruiting a deadenylating machinery whose activity is independent of translation and viral infection but might require a nuclear event.

The 5'-untranslated region of GM-CSF mRNA suppresses translational repression mediated by the 3' adenosine-uridine-rich element and the poly(A) tail

Granulocyte-macrophage colony stimulating factor (GM-CSF) mRNA levels are controlled post-transcriptionally by the 3'-untranslated region (UTR) adenosine-uridine-rich element (ARE). In untransformed, resting cells, the ARE targets GM-CSF mRNA for rapid degradation, thereby significantly suppressing protein expression. We used a rabbit reticulocyte lysate (RRL) cell-free system to examine translational regulation of GM-CSF expression. We uncoupled decay rates from rates of translation by programming the RRL with an excess of mRNAs. Capped, full-length, polyadenyl-ated human GM-CSF mRNA (full-length 5'-UTR AUUUA+A90) and an ARE-modified version (full-length 5'-UTR AUGUA+A90) produced identical amounts of protein. When the 5'-UTR was replaced with an irrelevant synthetic leader sequence (syn 5'-UTR), translation of syn 5'-UTR AUUUA+A90 mRNA was suppressed by >20-fold. Mutation of the ARE or removal of the poly(A) tail relieved this inhibition. Thus, in the absence of a native 5'-UTR, the ARE and poly(A) tail act in concert to block GM-CSF mRNA translation. Substitutions of different regions of the native 5'-UTR revealed that the entire sequence was essential in maintaining the highest rates of translation. However, shorter 10-12 nt contiguous 5'-UTR regions supported 50-60% of maximum translation. The 5'-UTR is highly conserved, suggesting similar regulation in multiple species and in these studies was the dominant element regulating GM-CSF mRNA translation, overriding the inhibitory effects of the ARE and the poly(A) tail.

Lipopolysaccharide inhibits the expression of the scavenger receptor Cla-1 in human monocytes and macrophages

Human Cla-1 is the likely homologue of the murine scavenger receptor class B type I (SR-BI). SR-BI mediates selective transfer of cholesterol to high-density lipoprotein (HDL) and the efflux of endogenously synthesized and plasma membrane sterols to HDL. HDL protects against atherosclerosis but also reduces endotoxic activity by complexation and neutralization of LPS. We found that Cla-1 is upregulated during phagocytic as well as dendritic differentiation of monocytes, indicating a function of this receptor for cholesterol homeostasis in phagocytes and antigen-presenting cells. Cla-1 expression is suppressed by the proinflammatory stimuli lipopolysaccharide, interferon-gamma, and tumor necrosis factor alpha in monocytes and macrophages. Downregulation of Cla-1 mRNA by LPS is likely due to a modification and subsequent destabilization of the mRNA. We propose that suppression of Cla-1 expression may help to stabilize the lipoprotein status in the blood compartment important for host defense.

Control of translation initiation in animals

Regulation of translation initiation is a central control point in animal cells. We review our current understanding of the mechanisms of regulation, drawing particularly on examples in which the biological consequences of the regulation are clear. Specific mRNAs can be controlled via sequences in their 5' and 3' untranslated regions (UTRs) and by alterations in the translation machinery. The 5'UTR sequence can determine which initiation pathway is used to bring the ribosome to the initiation codon, how efficiently initiation occurs, and which initiation site is selected. 5'UTR-mediated control can also be accomplished via sequence-specific mRNA-binding proteins. Sequences in the 3' untranslated region and the poly(A) tail can have dramatic effects on initiation frequency, with particularly profound effects in oogenesis and early development. The mechanism by which 3'UTRs and poly(A) regulate initiation may involve contacts between proteins bound to these regions and the basal translation apparatus. mRNA localization signals in the 3'UTR can also dramatically influence translational activation and repression. Modulations of the initiation machinery, including phosphorylation of initiation factors and their regulated association with other proteins, can regulate both specific mRNAs and overall translation rates and thereby affect cell growth and phenotype.

The polyadenylation inhibitor cordycepin (3'dA) causes a decline in c-MYC mRNA levels without affecting c-MYC protein levels

Study of the distribution of the poly(A) tail length of c-myc mRNA in several cell lines revealed a distinct, prevailing population with short poly(A) tails, derived through sequential deadenylation. To elucidate the possible in vivo function of this distinct short tailed c-myc mRNA population, the polyadenylation inhibitor cordycepin was used. This resulted in a decline in steady state c-myc mRNA levels with the remaining messenger mostly oligoadenylated. However, c-MYC proteins did not follow the reduction of the c-myc mRNA. On the other hand, in cells exposed to physiological agents known to downregulate c-myc expression, the reduction of mRNA steady state levels, was reflected upon c-MYC protein levels. The dissociation between c-myc mRNA and protein levels caused by cordycepin was not due to the stabilization of the c-MYC proteins and was not an indiscriminate effect since in the presence of cordycepin, c-fos mRNA and protein levels concomitantly declined. Our data indicate that under these conditions, a long poly(A) tail is not instrumental for c-myc mRNA translation and furthermore, the discrepancy in the steady state of c-myc mRNA level: c-MYC protein ratio between control cells and cells treated with cordycepin indicates that c-myc mRNA is subjected to translational control.

Control of the translational efficiency of beta-F1-ATPase mRNA depends on the regulation of a protein that binds the 3' untranslated region of the mRNA

The expression of the nucleus-encoded beta-F1-ATPase gene of oxidative phosphorylation is developmentally regulated in the liver at both the transcriptional and posttranscriptional levels. In this study we have analyzed the potential mechanisms that control the cytoplasmic expression of beta-F1-ATPase mRNA during liver development. Remarkably, a full-length 3' untranslated region (UTR) of the transcript is required for its efficient in vitro translation. When the 3' UTR of beta-F1-ATPase mRNA is placed downstream of a reporter construct, it functions as a translational enhancer. In vitro translation experiments with full-length beta-F1-ATPase mRNA and with a chimeric reporter construct containing the 3' UTR of beta-F1-ATPase mRNA suggested the existence of an inhibitor of beta-F1-ATPase mRNA translation in the fetal liver. Electrophoretic mobility shift assays and UV cross-linking experiments allowed the identification of an acutely regulated protein (3'betaFBP) of the liver that binds at the 3' UTR of beta-F1-ATPase mRNA. The developmental profile of 3'betaFBP parallels the reported changes in the translational efficiency of beta-F1-ATPase mRNA during development. Fractionation of fetal liver extracts revealed that the inhibitory activity of beta-F1-ATPase mRNA translation cofractionates with 3'-UTR band-shifting activity. Compared to other tissues of the adult rat, kidney and spleen extracts showed very high expression levels of 3'betaFBP. Translation of beta-F1-ATPase mRNA in the presence of kidney and spleen extracts further supported a translational inhibitory role for 3'betaFBP. Mapping experiments and a deletion mutant of the 3' UTR revealed that the cis-acting element for binding 3'betaFBP is located within a highly conserved region of the 3' UTR of mammalian beta-F1-ATPase mRNAs. Overall, we have identified a mechanism of translational control that regulates the rapid postnatal differentiation of liver mitochondria.