Germinal Center B-Cell-Associated Nuclear Protein (GANP) Involved in RNA Metabolism for B Cell Maturation

Arginine Methylation in Brain Tumors: Tumor Biology and Therapeutic Strategies

Protein arginine methylation is a common post-translational modification that plays a pivotal role in cellular regulation. Protein arginine methyltransferases (PRMTs) catalyze the modification of target proteins by adding methyl groups to the guanidino nitrogen atoms of arginine residues. Protein arginine methylation takes part in epigenetic and cellular regulation and has been linked to neurodegenerative diseases, metabolic diseases, and tumor progression. Aberrant expression of PRMTs is associated with the development of brain tumors such as glioblastoma and medulloblastoma. Identifying PRMTs as plausible contributors to tumorigenesis has led to preclinical and clinical investigations of PRMT inhibitors for glioblastoma and medulloblastoma therapy. In this review, we discuss the role of arginine methylation in cancer biology and provide an update on the use of small molecule inhibitors of PRMTs to treat glioblastoma, medulloblastoma, and other cancers.

Bioinformatic profiling of prognosis-related genes in the breast cancer immune microenvironment

In the microenvironment of breast cancer, immune cell infiltration is associated with an improved prognosis. To identify immune-related prognostic markers and therapeutic targets, we determined the lymphocyte-specific kinase (LCK) metagene scores of samples from breast cancer patients in The Cancer Genome Atlas. The LCK metagene score correlated highly with other immune-related scores, as well as with the clinical stage, prognosis and tumor suppressor gene mutation status (BRCA2, TP53, PTEN) of patients in the four breast cancer subtypes. A weighted gene co-expression network analysis was performed to detect representative genes from LCK metagene-related gene modules. In two of these modules, the levels of the co-expressed genes correlated highly with LCK metagene levels, so we conducted an enrichment analysis to discover their functions. We also identified differentially expressed genes in samples with high and low LCK metagene scores. By examining the overlapping results from these analyses, we obtained 115 genes, and found that 22 of them were independent predictors of overall survival in breast cancer patients. These genes were validated for their prognostic and diagnostic value with external data sets and paired tumor and non-tumor tissues. The genes identified herein could serve as diagnostic/prognostic markers and immune-related therapeutic targets in breast cancer.

Recalling the Future: Immunological Memory Toward Unpredictable Influenza Viruses

Persistent and durable immunological memory forms the basis of any successful vaccination protocol. Generation of pre-existing memory B cell and T cell pools is thus the key for maintaining protective immunity to seasonal, pandemic and avian influenza viruses. Long-lived antibody secreting cells (ASCs) are responsible for maintaining antibody levels in peripheral blood. Generated with CD4⁺ T help after naïve B cell precursors encounter their cognate antigen, the linked processes of differentiation (including Ig class switching) and proliferation also give rise to memory B cells, which then can change rapidly to ASC status after subsequent influenza encounters. Given that influenza viruses evolve rapidly as a consequence of antibody-driven mutational change (antigenic drift), the current influenza vaccines need to be reformulated frequently and annual vaccination is recommended. Without that process of regular renewal, they provide little protection against “drifted” (particularly H3N2) variants and are mainly ineffective when a novel pandemic (2009 A/H1N1 “swine” flu) strain suddenly emerges. Such limitation of antibody-mediated protection might be circumvented, at least in part, by adding a novel vaccine component that promotes cross-reactive CD8⁺ T cells specific for conserved viral peptides, presented by widely distributed HLA types. Such “memory” cytotoxic T lymphocytes (CTLs) can rapidly be recalled to CTL effector status. Here, we review how B cells and follicular T cells are elicited following influenza vaccination and how they survive into a long-term memory. We describe how CD8⁺ CTL memory is established following influenza virus infection, and how a robust CTL recall response can lead to more rapid virus elimination by destroying virus-infected cells, and recovery. Exploiting long-term, cross-reactive CTL against the continuously evolving and unpredictable influenza viruses provides a possible mechanism for preventing a disastrous pandemic comparable to the 1918-1919 H1N1 “Spanish flu,” which killed more than 50 million people worldwide.

Immunological responses against hepatitis B virus in human peripheral blood mononuclear cell-engrafted mice

It is well known that immune-mediated virus elimination is necessary for the treatment of HBV infection. Reconstitution of human immune cells in liver chimeric mice is warranted to understand the immunopathogenesis of HBV infection. Here, we report a new immunologically humanized mouse model with a human immune system via reconstitution of immunodeficient NOG-Iaβ/β2 m double KO mice, which are NOG mice that are deficient in both MHC class I and II (DKO-NOG mice), with human HLA-A2-positive peripheral blood mononuclear cells (PBMCs). After injection of PBMCs, the xenogeneic graft-versus-host disease observed in PBMC-engrafted NOG mice was prevented in PBMC-engrafted DKO-NOG mice. Liver damage was reduced, and the survival time was prolonged in human PBMC-engrafted DKO-NOG mice compared to those in the NOG mice. The expression levels of PD-1 and Tim-3 on human T cells from PBMC-engrafted DKO-NOG mice were lower than those from NOG mice. By induction of HBV-specific T cell responses, such as vaccination with HBc-derived, peptide-pulsed DCs, hydrodynamic injection of HBV vector and intrasplenic injection of HepG2.2.15, the number of HBc-derived, peptide-specific CTLs increased in PBMC-engrafted DKO-NOG mice. Moreover, the recombinant HBV vaccine resulted in the production of hepatitis B surface antibody in 50% of the vaccinated mice. The induction of HBV-specific immune responses could be established in the immunologically humanized mice.

Integrity of immunoglobulin variable regions is supported by GANP during AID-induced somatic hypermutation in germinal center B cells

Immunoglobulin affinity maturation depends on somatic hypermutation (SHM) in immunoglobulin variable (IgV) regions initiated by activation-induced cytidine deaminase (AID). AID induces transition mutations by C→U deamination on both strands, causing C:G→T:A. Error-prone repairs of U by base excision and mismatch repairs (MMRs) create transversion mutations at C/G and mutations at A/T sites. In Neuberger’s model, it remained to be clarified how transition/transversion repair is regulated. We investigate the role of AID-interacting GANP (germinal center-associated nuclear protein) in the IgV SHM profile. GANP enhances transition mutation of the non-transcribed strand G and reduces mutation at A, restricted to GYW of the AID hotspot motif. It reduces DNA polymerase η hotspot mutations associated with MMRs followed by uracil-DNA glycosylase. Mutation comparison between IgV complementary and framework regions (FWRs) by Bayesian statistical estimation demonstrates that GANP supports the preservation of IgV FWR genomic sequences. GANP works to maintain antibody structure by reducing drastic changes in the IgV FWR in affinity maturation.