Mitochondrial Haemoglobin Is Upregulated with Hypoxia in Skeletal Muscle and Has a Conserved Interaction with ATP Synthase and Inhibitory Factor 1.

The globin protein superfamily has diverse functions. Haemoglobin has been found in non-erythroid locations, including within the mitochondria. Using co-immunoprecipitation and in silico methods, we investigated the interaction of mitochondrial haemoglobin with ATP synthase and its associated proteins, including inhibitory factor 1 (IF1). We measured the expression of mitochondrial haemoglobin in response to hypoxia. In vitro and in silico evidence of interactions between mitochondrial haemoglobin and ATP synthase were found, and we report upregulated mitochondrial haemoglobin expression in response to hypoxia within skeletal muscle tissue. Our observations indicate that mitochondrial pH and ATP synthase activity are implicated in the mitochondrial haemoglobin response to hypoxia.

Proteomic analysis of the ATP synthase interactome in notothenioids highlights a pathway that inhibits ceruloplasmin production.

Antarctic notothenioids have unique adaptations that allow them to thrive in subzero Antarctic waters. Within the suborder Notothenioidei, species of the family Channichthyidae (icefish) lack hemoglobin and in some instances myoglobin too. In studies of mitochondrial function of notothenioids, few have focused specifically on ATP synthase. In this study, we find that the icefish Champsocephalus gunnari has a significantly higher level of ATP synthase subunit α expression than the red-blooded Notothenia rossii, but a much smaller interactome than the other species. We characterize the interactome of ATP synthase subunit α in two red-blooded species Trematomus bernacchii, N. rossii, and in the icefish Chionodraco rastrospinosus and C. gunnari and find that, in comparison with the other species, reactome enrichment for C. gunnari lacks chaperonin-mediated protein folding, and fewer oxidative-stress-associated proteins are present in the identified interactome of C. gunnari. Reactome enrichment analysis also identifies a transcript-specific translational silencing pathway for the iron oxidase protein ceruloplasmin, which has previously been reported in studies of icefish as distinct from other red-blooded fish and vertebrates in its activity and RNA transcript expression. Ceruloplasmin protein expression is detected by Western blot in the liver of T. bernacchii, but not in N. rossii, C. rastrospinosus, and C. gunnari. We suggest that the translation of ceruloplasmin transcripts is silenced by the identified pathway in icefish notothenioids, which is indicative of altered iron metabolism and Fe(II) detoxification.

Enhanced Cross-Reactive and Polyfunctional Effector-Memory T Cell Responses by ICVAX-a Human PD1-Based Bivalent HIV-1 Gag-p41 Mosaic DNA Vaccine.

Vaccine-induced protective T cell immunity is necessary for HIV-1 functional cure. We previously reported that rhesus PD1-Gag-based DNA vaccination sustained simian-human immunodeficiency virus (SHIV) suppression by inducing effector-memory CD8+ T cells. Here, we investigated a human PD1-Gag-based DNA vaccine, namely, ICVAX, for clinical translation. PD1-based dendritic cell targeting and mosaic antigenic designs were combined to generate the ICVAX by fusing the human soluble PD1 domain with a bivalent HIV-1 Gag-p41 mosaic antigen. The mosaic antigen was cross-reactive with patients infected with B, CRF07/08_BC, and CRF01_AE variants. In mice, ICVAX elicited stronger, broader, and more polyfunctional T cell responses than mosaic Gag-p41 alone, and suppressed EcoHIV infection more efficiently. In macaques, ICVAX elicited polyfunctional effector-memory T cell responses that targeted multiple nonoverlapping epitopes of the Gag-p41 antigen. Furthermore, ICVAX manufactured following good manufacturing practices proved potent immunogenicity in macaques after biannual homologous vaccination, warranting clinical evaluation of ICVAX as an immunotherapy against HIV-1. IMPORTANCE This study presents that ICVAX, a PD1-based DNA vaccine against HIV-1, could induce broad and polyfunctional T cell responses against different HIV-1 subtypes. ICVAX encodes a recombinant antigen consisting of the human soluble PD1 domain fused with two mosaic Gag-p41 antigens. The mosaic antigens cover more than 500 HIV-1 strains circulating in China including the subtypes B/B', CRF01_AE, and CRF07/08_BC. In mice, ICVAX elicited stronger, broader, and more polyfunctional T cell responses, with better EcoHIV suppression than the nontargeting mosaic Gag-p41 DNA vaccine. Moreover, both lab-generated and GMP-grade ICVAX also elicited strong polyfunctional effector-memory T cell responses in rhesus macaques with good immunogenicity against multiple nonoverlapping epitopes of the Gag-p41 antigen. This study therefore highlights the great potential to translate the PD1-based DNA vaccine approach into clinical use, and opens up new avenues for alternative HIV-1 vaccine design for HIV-1 preventive and functional cure.

BRD2 inhibition blocks SARS-CoV-2 infection by reducing transcription of the host cell receptor ACE2.

SARS-CoV-2 infection of human cells is initiated by the binding of the viral Spike protein to its cell-surface receptor ACE2. We conducted a targeted CRISPRi screen to uncover druggable pathways controlling Spike protein binding to human cells. Here we show that the protein BRD2 is required for ACE2 transcription in human lung epithelial cells and cardiomyocytes, and BRD2 inhibitors currently evaluated in clinical trials potently block endogenous ACE2 expression and SARS-CoV-2 infection of human cells, including those of human nasal epithelia. Moreover, pharmacological BRD2 inhibition with the drug ABBV-744 inhibited SARS-CoV-2 replication in Syrian hamsters. We also found that BRD2 controls transcription of several other genes induced upon SARS-CoV-2 infection, including the interferon response, which in turn regulates the antiviral response. Together, our results pinpoint BRD2 as a potent and essential regulator of the host response to SARS-CoV-2 infection and highlight the potential of BRD2 as a therapeutic target for COVID-19.

Low CCR5 expression protects HIV-specific CD4+ T cells of elite controllers from viral entry.

HIV elite controllers maintain a population of CD4 + T cells endowed with high avidity for Gag antigens and potent effector functions. How these HIV-specific cells avoid infection and depletion upon encounter with the virus remains incompletely understood. Ex vivo characterization of single Gag-specific CD4 + T cells reveals an advanced Th1 differentiation pattern in controllers, except for the CCR5 marker, which is downregulated compared to specific cells of treated patients. Accordingly, controller specific CD4 + T cells show decreased susceptibility to CCR5-dependent HIV entry. Two controllers carried biallelic mutations impairing CCR5 surface expression, indicating that in rare cases CCR5 downregulation can have a direct genetic cause. Increased expression of ß-chemokine ligands upon high-avidity antigen/TCR interactions contributes to autocrine CCR5 downregulation in controllers without CCR5 mutations. These findings suggest that genetic and functional regulation of the primary HIV coreceptor CCR5 play a key role in promoting natural HIV control.

Exercising D. melanogaster Modulates the Mitochondrial Proteome and Physiology. The Effect on Lifespan Depends upon Age and Sex.

Ageing is a major risk factor for many of the most prevalent diseases, including neurodegenerative diseases, cancer, and heart disease. As the global population continues to age, behavioural interventions that can promote healthy ageing will improve quality of life and relieve the socioeconomic burden that comes with an aged society. Exercise is recognised as an effective intervention against many diseases of ageing, but we do not know the stage in an individual's lifetime at which exercise is most effective at promoting healthy ageing, and whether or not it has a direct effect on lifespan. We exercised w1118 Drosophila melanogaster, investigating the effects of sex and group size at different stages of their lifetime, and recorded their lifespan. Climbing scores at 30 days were measured to record differences in fitness in response to exercise. We also assessed the mitochondrial proteome of w1118 Drosophila that had been exercised for one week, alongside mitochondrial respiration measured using high-resolution respirometry, to determine changes in mitochondrial physiology in response to exercise. We found that age-targeted exercise interventions improved the lifespan of both male and female Drosophila, and grouped males exercised in late life had improved climbing scores when compared with those exercised throughout their entire lifespan. The proteins of the electron transport chain were significantly upregulated in expression after one week of exercise, and complex-II-linked respiration was significantly increased in exercised Drosophila. Taken together, our findings provide a basis to test specific proteins, and complex II of the respiratory chain, as important effectors of exercise-induced healthy ageing.

Low-Power Sonication Can Alter Extracellular Vesicle Size and Properties.

Low-power sonication is widely used to disaggregate extracellular vesicles (EVs) after isolation, however, the effects of sonication on EV samples beyond dispersion are unclear. The present study analysed the characteristics of EVs collected from mesenchymal stem cells (MSCs) after sonication, using a combination of transmission electron microscopy, direct stochastic optical reconstruction microscopy, and flow cytometry techniques. Results showed that beyond the intended disaggregation effect, sonication using the lowest power setting available was enough to alter the size distribution, membrane integrity, and uptake of EVs in cultured cells. These results point to the need for a more systematic analysis of sonication procedures to improve reproducibility in EV-based cellular experiments.

SARS-CoV-2 infection induces the dedifferentiation of multiciliated cells and impairs mucociliary clearance.

Understanding how SARS-CoV-2 spreads within the respiratory tract is important to define the parameters controlling the severity of COVID-19. Here we examine the functional and structural consequences of SARS-CoV-2 infection in a reconstructed human bronchial epithelium model. SARS-CoV-2 replication causes a transient decrease in epithelial barrier function and disruption of tight junctions, though viral particle crossing remains limited. Rather, SARS-CoV-2 replication leads to a rapid loss of the ciliary layer, characterized at the ultrastructural level by axoneme loss and misorientation of remaining basal bodies. Downregulation of the master regulator of ciliogenesis Foxj1 occurs prior to extensive cilia loss, implicating this transcription factor in the dedifferentiation of ciliated cells. Motile cilia function is compromised by SARS-CoV-2 infection, as measured in a mucociliary clearance assay. Epithelial defense mechanisms, including basal cell mobilization and interferon-lambda induction, ramp up only after the initiation of cilia damage. Analysis of SARS-CoV-2 infection in Syrian hamsters further demonstrates the loss of motile cilia in vivo. This study identifies cilia damage as a pathogenic mechanism that could facilitate SARS-CoV-2 spread to the deeper lung parenchyma.

New Approaches to Tay-Sachs Disease Therapy.

Tay-Sachs disease belongs to the group of autosomal-recessive lysosomal storage metabolic disorders. This disease is caused by ß-hexosaminidase A (HexA) enzyme deficiency due to various mutations in α-subunit gene of this enzyme, resulting in GM2 ganglioside accumulation predominantly in lysosomes of nerve cells. Tay-Sachs disease is characterized by acute neurodegeneration preceded by activated microglia expansion, macrophage and astrocyte activation along with inflammatory mediator production. In most cases, the disease manifests itself during infancy, the "infantile form," which characterizes the most severe disorders of the nervous system. The juvenile form, the symptoms of which appear in adolescence, and the most rare form with late onset of symptoms in adulthood are also described. The typical features of Tay-Sachs disease are muscle weakness, ataxia, speech, and mental disorders. Clinical symptom severity depends on residual HexA enzymatic activity associated with some mutations. Currently, Tay-Sachs disease treatment is based on symptom relief and, in case of the late-onset form, on the delay of progression. There are also clinical reports of substrate reduction therapy using miglustat and bone marrow or hematopoietic stem cell transplantation. At the development stage there are methods of Tay-Sachs disease gene therapy using adeno- or adeno-associated viruses as vectors for the delivery of cDNA encoding α and ß HexA subunit genes. Effectiveness of this approach is evaluated in α or ß HexA subunit defective model mice or Jacob sheep, in which Tay-Sachs disease arises spontaneously and is characterized by the same pathological features as in humans. This review discusses the possibilities of new therapeutic strategies in Tay-Sachs disease therapy aimed at preventing neurodegeneration and neuroinflammation.

Rapid and accurate analysis of stem cell-derived extracellular vesicles with super resolution microscopy and live imaging.

Extracellular vesicles (EVs) have prevalent roles in cancer biology and regenerative medicine. Conventional techniques for characterising EVs including electron microscopy (EM), nanoparticle tracking analysis (NTA) and tuneable resistive pulse sensing (TRPS), have been reported to produce high variability in particle count (EM) and poor sensitivity in detecting EVs below 50 nm in size (NTA and TRPS), making accurate and unbiased EV analysis technically challenging. This study introduces direct stochastic optical reconstruction microscopy (d-STORM) as an efficient and reliable characterisation approach for stem cell-derived EVs. Using a photo-switchable lipid dye, d-STORM imaging enabled rapid detection of EVs down to 20-30 nm in size with higher sensitivity and lower variability compared to EM, NTA and TRPS techniques. Imaging of EV uptake by live stem cells in culture further confirmed the potential of this approach for downstream cell biology applications and for the analysis of vesicle-based cell-cell communication.

CCR5 Revisited: How Mechanisms of HIV Entry Govern AIDS Pathogenesis.

The chemokine receptor CCR5 has been the focus of intensive studies since its role as a coreceptor for HIV entry was discovered in 1996. These studies lead to the development of small molecular drugs targeting CCR5, with maraviroc becoming in 2007 the first clinically approved chemokine receptor inhibitor. More recently, the apparent HIV cure in a patient transplanted with hematopoietic stem cells devoid of functional CCR5 rekindled the interest for inactivating CCR5 through gene therapy and pharmacological approaches. Fundamental research on CCR5 has also been boosted by key advances in the field of G-protein coupled receptor research, with the realization that CCR5 adopts a variety of conformations, and that only a subset of these conformations may be targeted by chemokine ligands. In addition, recent genetic and pathogenesis studies have emphasized the central role of CCR5 expression levels in determining the risk of HIV and SIV acquisition and disease progression. In this article, we propose to review the key properties of CCR5 that account for its central role in HIV pathogenesis, with a focus on mechanisms that regulate CCR5 expression, conformation, and interaction with HIV envelope glycoproteins.

DNA Vaccination by Electroporation Amplifies Broadly Cross-Restricted Public TCR Clonotypes Shared with HIV Controllers.

Rare patients who spontaneously control HIV replication provide a useful model to inform HIV vaccine development. HIV controllers develop particularly efficient antiviral CD4+ T cell responses mediated by shared high-affinity TCRs. To determine whether the candidate DNA vaccine ADVAX could induce similar responses, we analyzed Gag-specific primary CD4+ T cells from healthy volunteers who received ADVAX DNA by electroporation. Vaccinated volunteers had an immunodominant response to the Gag293 epitope with a functional avidity intermediate between that of controllers and treated patients. The TCR repertoire of Gag293-specific CD4+ T cells proved highly biased, with a predominant usage of the TCRß variable gene 2 (TRBV2) in vaccinees as well as controllers. TCRα variable gene (TRAV) gene usage was more diverse, with the dominance of TRAV29 over TRAV24 genes in vaccinees, whereas TRAV24 predominated in controllers. Sequence analysis revealed an unexpected degree of overlap between the specific repertoires of vaccinees and controllers, with the sharing of TRAV24 and TRBV2 public motifs (>30%) and of public clonotypes characteristic of high-affinity TCRs. MHC class II tetramer binding revealed a broad HLA-DR cross-restriction, explaining how Gag293-specific public clonotypes could be selected in individuals with diverse genetic backgrounds. TRAV29 clonotypes also proved cross-restricted, but conferred responses of lower functional avidity upon TCR transfer. In conclusion, DNA vaccination by electroporation primed for TCR clonotypes that were associated with HIV control, highlighting the potential of this vaccine delivery method. To our knowledge, this study provides the first proof-of-concept that clonotypic analysis may be used as a tool to monitor the quality of vaccine-induced responses and modulate these toward "controller-like" responses.

MHC Class II Tetramer Labeling of Human Primary CD4+ T Cells from HIV Infected Patients.

Major Histocompatibility Complex (MHC) tetramers have been used for two decades to detect, isolate and characterize T cells specific for various pathogens and tumor antigens. In the context of Human Immunodeficiency Virus (HIV) infection, antigen-specific CD8+ T cells have been extensively studied ex vivo, as they can be readily detected by HIV peptide-loaded MHC class I tetramers. In contrast, the detection of HIV-specific CD4+ T cells has proven more challenging, due to the intrinsically lower clonal expansion rates of CD4+ T cells, and to the preferential depletion of HIV-specific CD4+ T cells in the course of HIV infection. In the following protocol, we describe a simple method that facilitates the identification of CD4+ T cells specific for an HIV-1 capsid epitope using peptide-loaded MHC class II tetramers. Tetramer labeled CD4+ T cells can be analyzed for their cell surface phenotype and/or FACS-sorted for further downstream applications. A key point for successful detection of specific CD4+ T cells ex vivo is the choice of a peptide/MHC II combination that results in high-affinity T Cell Receptor (TCR) binding ( Benati et al., 2016 ). A second key point for reliable detection of MHC II tetramer-positive cells is the systematic use of a control tetramer loaded with an irrelevant peptide, with the sample and control tubes being processed in identical conditions.

Mitochondrial proteomic profiling reveals increased carbonic anhydrase II in aging and neurodegeneration.

Carbonic anhydrase inhibitors are used to treat glaucoma and cancers. Carbonic anhydrases perform a crucial role in the conversion of carbon dioxide and water into bicarbonate and protons. However, there is little information about carbonic anhydrase isoforms during the process of ageing. Mitochondrial dysfunction is implicit in ageing brain and muscle. We have interrogated isolated mitochondrial fractions from young adult and middle aged mouse brain and skeletal muscle. We find an increase of tissue specific carbonic anhydrases in mitochondria from middle-aged brain and skeletal muscle. Mitochondrial carbonic anhydrase II was measured in the Purkinje cell degeneration (pcd5J) mouse model. In pcd5J we find mitochondrial carbonic anhydrase II is also elevated in brain from young adults undergoing a process of neurodegeneration. We show C.elegans exposed to carbonic anhydrase II have a dose related shorter lifespan suggesting that high CAII levels are in themselves life limiting. We show for the first time that the mitochondrial content of brain and skeletal tissue are exposed to significantly higher levels of active carbonic anhydrases as early as in middle-age. Carbonic anhydrases associated with mitochondria could be targeted to specifically modulate age related impairments and disease.

Biomarkers of CD4+ T-cell activation as risk factors for tuberculosis-associated immune reconstitution inflammatory syndrome.

OBJECTIVE: Patients coinfected with HIV and Mycobacterium tuberculosis frequently experience a paradoxical worsening of tuberculosis (TB) symptoms early after the initiation of combination antiretroviral therapy (cART). This immune reconstitution inflammatory syndrome (TB-IRIS) can lead to significant morbidity and needs to be distinguished from TB recurrence due to ineffective treatment. We investigated whether plasma biomarkers could predict the occurrence of TB-IRIS. DESIGN: ANRS 129 BKVIR is a single-arm multicentre trial that enrolled 69 cART-naïve HIV-1-infected patients treated for TB. The patients received once-daily tenofovir/emtricitabine/efavirenz first-line regimen. TB-IRIS cases (IRIS+) were validated by an Event Review Committee. METHODS: A panel of 26 plasma biomarkers was monitored longitudinally for 24 weeks from cART initiation onward, using multiplexed assays and high-sensitivity ELISA. Statistical analyses of biomarkers were adjusted for test multiplicity. RESULTS: One-third of patients (n=23) experienced TB-IRIS. The inflammatory cytokines and chemokines interleukin (IL)-6, IL-8, interferon-gamma-induced protein 10 (IP-10), and tumour necrosis factor-alpha (TNF-α) showed increased plasma levels at week 4 in IRIS-positive (IRIS+) patients (P<0.05 for each biomarker). The soluble IL-2 receptor sCD25, which is released upon CD4 T-cell activation, was significantly increased at week 0 in IRIS+ patients (P<0.05), and remained elevated throughout follow-up. IL-7, a key homeostatic cytokine for CD4 T-cells, showed a trend for higher values in the TB-IRIS group. Both sCD25 and IL-7 baseline levels were independently associated with a shorter time to TB-IRIS occurrence (P=0.005 and P=0.02, respectively). CONCLUSION: These findings support a role for CD4 T-cell activation prior to massive inflammation in the development of TB-IRIS.

HIV controllers maintain a population of highly efficient Th1 effector cells in contrast to patients treated in the long term.

HIV controllers are rare individuals who spontaneously control HIV replication in the absence of antiretroviral therapy. To identify parameters of the CD4 response that may contribute to viral control rather than merely reflect a persistently low viremia, we compared the T helper profiles in two groups of patients with more than 10 years of viral suppression: HIV controllers from the Agence Nationale de Recherche sur le SIDA et les Hépatites Virales (ANRS) CO18 cohort (n = 26) and efficiently treated patients (n = 16). Cells specific for immunodominant Gag and cytomegalovirus (CMV) peptides were evaluated for the production of 10 cytokines and cytotoxicity markers and were also directly quantified ex vivo by major histocompatibility complex (MHC) class II tetramer staining. HIV controller CD4(+) T cells were characterized by a higher frequency of gamma interferon (IFN-γ) production, perforin(+)/CD107a(+) expression, and polyfunctionality in response to Gag peptides. While interleukin 4 (IL-4), IL-17, and IL-21 production did not differ between groups, the cells of treated patients produced more IL-10 in response to Gag and CMV peptides, pointing to persistent negative immunoregulation after long-term antiretroviral therapy. Gag293 tetramer-positive cells were detected at a high frequency (0.12%) and correlated positively with IFN-γ-producing CD4(+) T cells in the controller group (R = 0.73; P = 0.003). Tetramer-positive cells were fewer in the highly active antiretroviral therapy (HAART) group (0.04%) and did not correlate with IFN-γ production, supporting the notion of a persistent immune dysfunction in HIV-specific CD4(+) T cells of treated patients. In conclusion, HIV controllers maintained a population of highly efficient Th1 effectors directed against Gag in spite of a persistently low antigenemia, while patients treated in the long term showed a loss of CD4 effector functions.

HIV controllers: a multifactorial phenotype of spontaneous viral suppression.

A small minority of HIV-infected individuals, known as HIV controllers, is able to exert long-term control over HIV replication in the absence of treatment. Increasing evidence suggests that the adaptive immune system plays a critical role in this control but also that a combination of several host and/or viral factors, rather than a single cause, leads to this rare phenotype. Here, we review recent advances in the study of these remarkable individuals. We summarize the epidemiology and clinical characteristics of HIV controllers, and subsequently describe contributing roles of host genetic factors, innate and adaptive immune responses, and viral factors to this phenotype. We emphasize distinctive characteristics of HIV-specific CD4 T cell responses and of CD4 T cell subpopulations that are frequently found in HIV controllers. We discuss major controversies in the field and the relevance of the study of HIV controllers for the development of novel therapeutic strategies and vaccines.

HIV controller CD4+ T cells respond to minimal amounts of Gag antigen due to high TCR avidity.

HIV controllers are rare individuals who spontaneously control HIV replication in the absence of antiretroviral treatment. Emerging evidence indicates that HIV control is mediated through very active cellular immune responses, though how such responses can persist over time without immune exhaustion is not yet understood. To investigate the nature of memory CD4+ T cells responsible for long-term anti-HIV responses, we characterized the growth kinetics, Vbeta repertoire, and avidity for antigen of patient-derived primary CD4+ T cell lines. Specific cell lines were obtained at a high rate for both HIV controllers (16/17) and efficiently treated patients (19/20) in response to the immunodominant Gag293 peptide. However, lines from controllers showed faster growth kinetics than those of treated patients. After normalizing for growth rates, IFN-gamma responses directed against the immunodominant Gag293 peptide showed higher functional avidity in HIV controllers, indicating differentiation into highly efficient effector cells. In contrast, responses to Gag161, Gag263, or CMV peptides did not differ between groups. Gag293-specific CD4+ T cells were characterized by a diverse Vbeta repertoire, suggesting that multiple clones contributed to the high avidity CD4+ T cell population in controllers. The high functional avidity of the Gag293-specific response could be explained by a high avidity interaction between the TCR and the peptide-MHC complex, as demonstrated by MHC class II tetramer binding. Thus, HIV controllers harbor a pool of memory CD4+ T cells with the intrinsic ability to recognize minimal amounts of Gag antigen, which may explain how they maintain an active antiviral response in the face of very low viremia.

Interaction of HIV-1 integrase with DNA repair protein hRad18.

We have previously shown that human immunodeficiency virus-1 (HIV-1) integrase is an unstable protein and a substrate for the N-end rule degradation pathway. This degradation pathway shares its ubiquitin-conjugating enzyme, Rad6, with the post-replication/translesion DNA repair pathway. Because DNA repair is thought to play an essential role in HIV-1 integration, we investigated whether other molecules of this DNA repair pathway could interact with integrase. We observed that co-expression of human Rad18 induced the accumulation of an otherwise unstable form of HIV-1 integrase. This accumulation occurred even though hRAD18 possesses a RING finger domain, a structure that is generally associated with E3 ubiquitin ligase function and protein degradation. Evidence for an interaction between integrase and hRad18 was obtained through reciprocal co-immunoprecipitation. Moreover we found that a 162-residue region of hRad18 (amino acids 65-226) was sufficient for both integrase stabilization and interaction. Finally, we observed that HIV-1 integrase co-localized with hRad18 in nuclear structures in a subpopulation of co-transfected cells. Taken together, these findings identify hRad18 as a novel interacting partner of HIV-1 integrase and suggest a role for post-replication/translesion DNA repair in the retroviral integration process.