Control of eukaryotic protein synthesis by upstream open reading frames in the 5'-untranslated region of an mRNA.

Control of gene expression is achieved at various levels. Translational control becomes crucial in the absence of transcription, such as occurs in early developmental stages. One of the initiating events in translation is that the 40 S subunit of the ribosome binds the mRNA at the 5'-cap structure and scans the 5'-untranslated region (5'-UTR) for AUG initiation codons. AUG codons upstream of the main open reading frame can induce formation of a translation-competent ribosome that may translate and (i) terminate and re-initiate, (ii) terminate and leave the mRNA, resulting in down-regulation of translation of the main open reading frame, or (iii) synthesize an N-terminally extended protein. In the present review we discuss how upstream AUGs can control the expression of the main open reading frame, and a comparison is made with other elements in the 5'-UTR that control mRNA translation, such as hairpins and internal ribosome entry sites. Recent data indicate the flexibility of controlling translation initiation, and how the mode of ribosome entry on the mRNA as well as the elements in the 5'-UTR can accurately regulate the amount of protein synthesized from a specific mRNA

Dendritic Cells Preferentially Transfer CXCR4-Using Human Immunodeficiency Virus Type 1 Variants to CD4+ T Lymphocytes in trans▿

Human immunodeficiency virus type 1 (HIV-1) preferentially utilizes the CCR5 coreceptor for target cell entry in the acute phase of infection, while later in disease progression the virus switches to the CXCR4 coreceptor in approximately 50% of patients. In response to HIV-1 the adaptive immune response is triggered, and antibody (Ab) production is elicited to block HIV-1 entry. We recently determined that dendritic cells (DCs) can efficiently capture Ab-neutralized HIV-1, restore infectivity, and transmit infectious virus to target cells. Here, we tested the effect of Abs on trans transmission of CCR5 or CXCR4 HIV-1 variants. We observed that transmission of HIV-1 by immature as well as mature DCs was significantly higher for CXCR4- than CCR5-tropic viral strains. Additionally, neutralizing Abs directed against either the gp41 or gp120 region of the envelope such as 2F5, 4E10, and V3-directed Abs inhibited transmission of CCR5-tropic HIV-1, whereas Ab-treated CXCR4-tropic virus demonstrated unaltered or increased transmission. To further study the effects of coreceptor usage we tested molecularly cloned HIV-1 variants with modifications in the envelope that were based on longitudinal gp120 V1 and V3 variable loop sequences from a patient progressing to AIDS. We observed that DCs preferentially facilitated infection of CD4+ T lymphocytes of viral strains with an envelope phenotype found late in disease. Taken together, our results illustrate that DCs transmit CXCR4-tropic HIV-1 much more efficiently than CCR5 strains; we hypothesize that this discrimination could contribute to the in vivo coreceptor switch after seroconversion and could be responsible for the increase in viral load

Reactivation of Neutralized HIV-1 by Dendritic Cells Is Dependent on the Epitope Bound by the Antibody

Ab-neutralized HIV-1 can be captured by dendritic cells (DCs), which subsequently transfer infectious HIV-1 to susceptible CD4(+) T cells. In this study, we examined the capacity of early Abs, as well as recently identified broadly neutralizing Abs (bNAbs) targeting different envelope glycoprotein (Env) epitopes, to block HIV-1 transmission by immature and mature DCs to HIV-1-sensitive cells. Three bNAbs directed against the gp41 membrane proximal region of Env (2F5, 4E10, and 10E8) and three gp120 bNAbs targeting the CD4 binding site (b12, VRC01, and NIH45-46) were examined. In addition, eight glycan-dependent bNAbs targeting the V1V2 apex (PG9, PG16, and PGT145), the V3 loop (2G12, PGT121, and PGT128), and the gp120-gp41 interface of Env (PGT151 and 35O22) were tested. bNAbs that bound specific glycans showed, depending on the immature or mature state of the DC, diverse efficiencies in HIV-1 trans-infection. All bNAbs that bound the CD4 binding site blocked trans-infection, whereas all bNAbs directed against the membrane proximal region lost neutralizing activity after DC-mediated HIV-1 transmission. To understand how preneutralized HIV-1 can be transferred as infectious virus by DCs, we followed the processing of 2F5-treated HIV-1 by DCs with confocal microscopy. Inhibition of DC-internalization pathways could not reverse the dissociation of 2F5 from HIV-1, suggesting that Ab dissociation occurs directly at the plasma membrane. Collectively, these findings imply that the location of the epitope and the neutralization capacity of these Abs determine the efficiency of DC-mediated HIV-1 transfer

Reactivation of Neutralized HIV-1 by Dendritic Cells Is Dependent on the Epitope Bound by the Antibody

Ab-neutralized HIV-1 can be captured by dendritic cells (DCs), which subsequently transfer infectious HIV-1 to susceptible CD4(+) T cells. In this study, we examined the capacity of early Abs, as well as recently identified broadly neutralizing Abs (bNAbs) targeting different envelope glycoprotein (Env) epitopes, to block HIV-1 transmission by immature and mature DCs to HIV-1-sensitive cells. Three bNAbs directed against the gp41 membrane proximal region of Env (2F5, 4E10, and 10E8) and three gp120 bNAbs targeting the CD4 binding site (b12, VRC01, and NIH45-46) were examined. In addition, eight glycan-dependent bNAbs targeting the V1V2 apex (PG9, PG16, and PGT145), the V3 loop (2G12, PGT121, and PGT128), and the gp120-gp41 interface of Env (PGT151 and 35O22) were tested. bNAbs that bound specific glycans showed, depending on the immature or mature state of the DC, diverse efficiencies in HIV-1 trans-infection. All bNAbs that bound the CD4 binding site blocked trans-infection, whereas all bNAbs directed against the membrane proximal region lost neutralizing activity after DC-mediated HIV-1 transmission. To understand how preneutralized HIV-1 can be transferred as infectious virus by DCs, we followed the processing of 2F5-treated HIV-1 by DCs with confocal microscopy. Inhibition of DC-internalization pathways could not reverse the dissociation of 2F5 from HIV-1, suggesting that Ab dissociation occurs directly at the plasma membrane. Collectively, these findings imply that the location of the epitope and the neutralization capacity of these Abs determine the efficiency of DC-mediated HIV-1 transfer

Vanishing white matter: deregulated integrated stress response as therapy target

Objective: Vanishing white matter (VWM) is a fatal, stress-sensitive leukodystrophy that mainly affects children and is currently without treatment. VWM is caused by recessive mutations in eukaryotic initiation factor 2B (eIF2B) that is crucial for initiation of mRNA translation and its regulation during the integrated stress response (ISR). Mutations reduce eIF2B activity. VWM pathomechanisms remain unclear. In contrast with the housekeeping function of eIF2B, astrocytes are selectively affected in VWM. One study objective was to test our hypothesis that in the brain translation of specific mRNAs is altered by eIF2B mutations, impacting primarily astrocytes. The second objective was to investigate whether modulation of eIF2B activity could ameliorate this altered translation and improve the disease. Methods: Mice with biallelic missense mutations in eIF2B that recapitulate human VWM were used to screen for mRNAs with altered translation in brain using polysomal profiling. Findings were verified in brain tissue from VWM patients using qPCR and immunohistochemistry. The compound ISRIB (for “ISR inhibitor”) was administered to VWM mice to increase eIF2B activity. Its effect on translation, neuropathology, and clinical signs was assessed. Results: In brains of VWM compared to wild-type mice we observed the most prominent changes in translation concerning ISR mRNAs; their expression levels correlated with disease severity. We substantiated these findings in VWM patients’ brains. ISRIB normalized expression of mRNA markers, ameliorated brain white matter pathology and improved motor skills in VWM mice. Interpretation: The present findings show that ISR deregulation is central in VWM pathomechanisms and a viable target for therapy