Maja Ilić Tomaš

Murine Cytomegalovirus Perturbs Endosomal Trafficking of Major Histocompatibility Complex Class I Molecules in the Early Phase of Infection

ABSTRACT Murine cytomegalovirus (MCMV) functions interfere with protein trafficking in the secretory pathway. In this report we used Δm138-MCMV, a recombinant virus with a deleted viral Fc receptor, to demonstrate that MCMV also perturbs endosomal trafficking in the early phase of infection. This perturbation had a striking impact on cell surface-resident major histocompatibility complex class I (MHC-I) molecules due to the complementary effect of MCMV immunoevasins, which block their egress from the secretory pathway. In infected cells, constitutively endocytosed cell surface-resident MHC-I molecules were arrested and retained in early endosomal antigen 1 (EEA1)-positive and lysobisphosphatidic acid (LBPA)-negative perinuclear endosomes together with clathrin-dependent cargo (transferrin receptor, Lamp1, and epidermal growth factor receptor). Their progression from these endosomes into recycling and degradative routes was inhibited. This arrest was associated with a reduction of the intracellular content of Rab7 and Rab11, small GTPases that are essential for the maturation of recycling and endolysosomal domains of early endosomes. The reduced recycling of MHC-I in Δm138-MCMV-infected cells was accompanied by their accelerated loss from the cell surface. The MCMV function that affects cell surface-resident MHC-I was activated in later stages of the early phase of viral replication, after the expression of known immunoevasins. MCMV without the three immunoevasins (the m04, m06, and m152 proteins) encoded a function that affects endosomal trafficking. This function, however, was not sufficient to reduce the cell surface expression of MHC-I in the absence of the transport block in the secretory pathway.

Cytomegalovirus immune evasion by perturbation of endosomal trafficking

Cytomegaloviruses (CMVs), members of the herpesvirus family, have evolved a variety of mechanisms to evade the immune response to survive in infected hosts and to establish latent infection. They effectively hide infected cells from the effector mechanisms of adaptive immunity by eliminating cellular proteins (major histocompatibility Class I and Class II molecules) from the cell surface that display viral antigens to CD8 and CD4 T lymphocytes. CMVs also successfully escape recognition and elimination of infected cells by natural killer (NK) cells, effector cells of innate immunity, either by mimicking NK cell inhibitory ligands or by downregulating NK cell-activating ligands. To accomplish these immunoevasion functions, CMVs encode several proteins that function in the biosynthetic pathway by inhibiting the assembly and trafficking of cellular proteins that participate in immune recognition and thereby, block their appearance at the cell surface. However, elimination of these proteins from the cell surface can also be achieved by perturbation of their endosomal route and subsequent relocation from the cell surface into intracellular compartments. Namely, the physiological route of every cellular protein, including immune recognition molecules, is characterized by specific features that determine its residence time at the cell surface. In this review, we summarize the current understanding of endocytic trafficking of immune recognition molecules and perturbations of the endosomal system during infection with CMVs and other members of the herpesvirus family that contribute to their immune evasion mechanisms.

Early endosomal rerouting of major histocompatibility class I conformers

Major histocompatibility class I (MHC‐I) molecules are present at the cell surface both as fully conformed trimolecular complexes composed of heavy chain (HC), beta‐2‐microglobulin (β2m) and peptide, and various open forms, devoid of peptide and/or β2m (open MHC‐I conformers). Fully conformed MHC‐I complexes and open MHC‐I conformers can be distinguished by well characterized monoclonal antibody reagents that recognize their conformational difference in the extracellular domain. In the present study, we used these tools in order to test whether conformational difference in the extracellular domain determines endocytic and endosomal route of plasma membrane (PM) proteins. We analyzed PM localization, internalization, endosomal trafficking, and recycling of human and murine MHC‐I proteins on various cell lines. We have shown that fully conformed MHC‐I and open MHC‐I conformers segregate at the PM and during endosomal trafficking resulting in the exclusion of open MHC‐I conformers from the recycling route. This segregation is associated with their partitioning into the membranes of different compositions. As a result, the open MHC‐I conformers internalized with higher rate than fully conformed counterparts. Thus, our data suggest the existence of conformation‐based protein sorting mechanism in the endosomal system. J. Cell. Physiol. 227: 2953–2964, 2012.

Endosomal trafficking of open Major Histocompatibility Class I conformers - Implications for presentation of endocytosed antigens

Major Histocompatibility Class I (MHC-I) molecules are present at the cell surface either as fully conformed trimolecular complexes composed of heavy chain, beta-2-microglobulin (β2m) and antigenic peptide or as various open forms, devoid of the peptide and/or β2m. While the role of fully conformed MHC-I is well studied, the physiological role of open conformers is neglected. We have shown that fully conformed MHC-I and open MHC-I conformers segregate at the PM and during endosomal trafficking resulting in the exclusion of open MHC-I from the early endosomal/juxtanuclear recycling route. As a result, open MHC-I conformers are internalized with a higher rate than fully conformed counterparts. Although the majority of internalized open MHC-I is directed into the acidic late endosomal (LE) compartments, only a fraction of them is degraded. Namely, a significant fraction of open MHC-I is present in a subset of LEs with the capacity of recycling and/or exocytosis. Therefore, it should be examined whether exogenous peptide loading may occur during traveling of MHC-I proteins through LE compartments, especially in a subset of less acidic LEs that detach from the core of perinuclear acidic LEs and migrate toward the cell periphery. Given that the acidic LE environment is not favorable for peptide loading, an endosomal compartment with the recycling capacity and less acidic environment that allows stabilization of newly formed trimolecular complexes is proper site for exogenous peptide loading. We propose that a LE compartment which collect and retain open MHC-I conformers should be taken into consideration as a site of exogenous peptide loading.

How activity of inflammatory bowel disease influences bone loss.

Bone loss is a common problem for individuals with inflammatory bowel disease (IBD). The aim of our study was to assess bone mineral density (BMD) in patients with IBD and to investigate the role of corticosteroid (CS) use and duration and activity of disease on BMD. Ninety-two patients (56 men and 36 women) with IBD, of whom 32 had ulcerative colitis (UC) and 60 had Crohns disease (CD), underwent clinical assessment. Lumbar and femoral neck BMDs were measured by dual-energy X-ray absorptiometry. Osteopenia was observed in 14 patients (43%) with UC and in 24 patients (40%) with CD (p=0.187). Four patients (12%) with UC and 7 patients (11%) with CD had osteoporosis (p=0.308). Femoral BMD decreased in patients with long duration of CS use and correlated inversely with disease activity. Multiple regression analysis of BMD showed that statistically significant risk factors were duration of active disease and body mass index as well. Based on our results, it is necessary to take into account the risk of decreased BMD in patients with IBD. It is most important to achieve disease remission as soon as possible in addition to nutritional support.

Comparative study of frequency of different lymphocytes subpopulation in peripheral blood of patients with prostate cancer and benign prostatic hyperplasia

ZusammenfassungZIEL: Benigne Prostatahyperplasie (BPH) und Prostatakrebs (PC) sind die häufigsten urologischen Erkrankungen bei Männern über fünfzig und sie wurden vor kurzem für das Ergebnis einer gestörten Immunantwort gehalten. Trotz vieler Studien zur auf T-Zellen basierten Anti-Tumor-Immunität, kann die Rolle der angeborenen Immunzellen bei BPH und PC noch immer schlecht verstanden werden. In dieser Studie wurde die Frequenz von verschiedenen Leukozytensubpopulationen im peripheren Blut von sowohl BPH- und PC-Patienten als auch von gesunden Probanden analysiert und gegenseitig verglichen. METHODEN: 60 Probanden wurden in eine Querschnittsstudie eingeschlossen (20 Patienten mit BPH, 20 Patienten mit PC und 20 gesunde Probanden). Mononukleäre Zellen des peripheren Blutes (PBMC) wurden isoliert und sowohl der Prozentsatz von T-Lymphozyten, natürlichen Killerzellen (NK) und natürlichen Killer-T-Zellen (NKT) als auch der Prozentsatz von Subsets der T-Lymphozyten [CD3+CD56–CD4+, TReg (CD4+CD25+FoxP3+) und CD3+CD56–CD8+] und der NK-Zellen (CD3–CD56+dim und CD3–CD56+bright) wurden mit Durchflusszytometrie analysiert. Auch der intrazelluläre Inhalt von Interleukin-4 (IL-4) und Gamma-Interferon (IFN-γ) wurde in T-Lymphozyten, NK- und NKT-Zellen gefunden. ERGEBNISSE: Das Prozent von T-Lymphozyten und deren Subsets in Lymphozyten des peripheren Blutes unterschied sich nicht unter den untersuchten Gruppen, während die Frequenz der regulatorischen T-Zellen (TReg) die höchste bei der PC-Patienten war. Höherer Anteil der B-Lymphozyten und NKT-Zellen wurde in Lymphozyten des peripheren Blutes von BPH-Patienten beobachtet. Der Anteil der NK-Zellen und deren Subsets unterschied sich nicht unter den untersuchten Gruppen. Eine negative Korrelation zwischen dem PSA-Wert und dem Prozentsatz der T-Lymphozyten und NK-Zellen wurde nur bei PC-Patienten bemerkt. Sehr positive Korrelation zwischen dem PSA-Wert und dem Prozentsatz der regulatorischen T-Zellen (TReg) stellte man bei PC-Patienten fest. SCHLUSSFOLGERUNG: Unterschiedliche Frequenz der verschiedenen Lymphozytensubpopulationen im peripheren Blut von gesunden Männern und BPH- und PC-Patienten könnte für das Auftreten und Fortschreiten der Prostatahyperplasie oder des Tumors verantwortlich sein. Aufgrund der Tumorfähigkeit, T-Zell-Immunantwort zu unterdrücken, könnten die Zellen der angeborenen Immunität (NKT-Zellen und regulatorische T-Zellen) die zentrale Rolle in der Immunpathogenese von PC und BPH spielen.SummaryPURPOSE: Benign prostatic hyperplasia (BPH) and prostate cancer (PC) are the most common urologic diseases among men over fifty and, until recently, they were considered to be caused by the impaired immune response. Despite many studies designed to investigate T-cell-based antitumor immunity, the role of innate immune cells in BPH and PC is still poorly understood. In this study the frequency of different leukocytes subpopulation in peripheral blood of BPH, PC patients and in healthy volunteers was analysed and compared. METHODS: In a cross-sectional study 60 subjects were enrolled (20 patients with BPH or with PC and 20 healthy volunteers). Peripheral blood mononuclear cells (PBMC) were isolated and the percentage of T lymphocytes, natural killer (NK) and NKT cells, as well as subsets of T lymphocytes [CD3+CD56–CD4+, Tregs (CD4+CD25+FoxP3+) and CD3+CD56–CD8+] and NK cells (CD3–CD56+dim and CD3–CD56+bright) were analysed by flow cytometry. Intracellular content of interleukin-4 (IL-4) and interferon gamma (IFNγ in T lymphocytes, NK and NKT cells were also detected. RESULTS: The percentage of T lymphocytes and their subsets in peripheral blood lymphocytes did not differ among investigated groups, while the frequency of Tregs was the highest in PC patients. The percentage of NK cell and their subsets did not differ among investigated groups. Negative correlation between PSA value, percentage of T lymphocytes and NK cells was observed only in PC patients. Highly positive correlation between the PSA value and the percentage of Tregs was found in PC patients. CONCLUSION: Different frequencies in distinctly lymphocyte subpopulation in peripheral blood of healthy men, BPH and PC patients could be responsible for occurrence and progression of prostatic hyperplasia or tumour. Due to the ability of tumours to suppress the cognate T cell immune response, the cells of innate immunity (NKT and Tregs) may be playing a key role in the immunopathogenesis of PC and BPH.

Different Perforin Expression in Peripheral Blood and Prostate Tissue in Patients with Benign Prostatic Hyperplasia and Prostate Cancer

Perforin (P) is a prototypical cytotoxic molecule involved in cell‐mediated immunity against various pathogens, alloantigens and particularly different tumours. The purpose of this study was to determine P expression in different lymphocyte subpopulations isolated from peripheral blood and prostate tissue of patients with benign prostatic hyperplasia (BPH) and prostate cancer (PCa) and compare it with the P expression found in the control group. Twenty subjects were recruited in each of the groups. Prostate mononuclear cells of the BPH and PCa tissues were isolated by enzymatic digestion and gradient density centrifugation, whereas peripheral blood mononuclear cells were isolated by gradient density centrifugation alone. Cells and tissue samples were labelled using monoclonal antibodies against P and different surface antigens (CD3, CD4, CD8 and CD56) and analysed by immunofluorescence and flow cytometry. Total P expression in peripheral blood lymphocytes did not differ significantly between BPH/PCa patients and control group, although the BPH and PCa tissue showed lower P expression level. A negative correlation between prostate‐specific antigen levels and the overall percentage of P+, CD3+CD56−P+, and CD3−CD56+P+ cells in the prostate tissue was observed only in patients with PCa. Our findings indicate that the low frequency of P+ lymphocytes, including T, NKT and NK cells, in the prostate tissue of patients with BPH and, particularly, PCa could be the consequence of local tissue microenvironment and one of the mechanisms involved in the pathogenesis of prostate hyperplasia following malignant alteration.

Landmarks of endosomal remodeling in the early phase of cytomegalovirus infection

Cytomegaloviruses (CMVs) extensively rearrange the cellular membrane system to develop assembly compartment (AC), but the earliest events in this process are poorly characterized. Here, we demonstrate that murine CMV (MCMV) infection restrains endosomal trafficking of cargo molecules that travel along the recycling (TfR and MHC-I) and the late endosomal (EGFR, M6PR, Lamp1) circuit. Internalized cargo accumulates in Arf6-, Rab5-, Rab22A-, and Rab11-positive and Rab35-, Rab8-, and Rab10-negative juxtanuclear endosomes, suggesting the disruption of Arf/Rab regulatory cascade at the stage of sorting endosomes and the endosomal recycling compartment. Rearrangement of the endosomal system is initiated by an MCMV-encoded function very early in the infection. Our study, thus, establishes a set of landmarks of endosomal remodeling in the early phase of MCMV-infection which coincide with the Golgi rearrangement, suggesting that these perturbations are the earliest membrane reorganizations that may represent an initial step in the biogenesis of the AC.