The RAC2-PI3K axis regulates human NK cell maturation and function

Identification of a Prognostic Model Based on NK Cell-Related Genes in Multiple Myeloma Using Single-Cell and Transcriptomic Data Analysis

Background

Multiple myeloma (MM), an incurable plasma cell malignancy. The significance of the relationship between natural killer (NK) cell-related genes and clinical factors in MM remains unclear.

Methods

Initially, we extracted NK cell-related genes from peripheral blood mononuclear cells (PBMC) of healthy donors and MM samples by employing single-cell transcriptome data analysis in TISCH2. Subsequently, we screened NK cell-related genes with prognostic significance through univariate Cox regression analysis and protein-protein interaction (PPI) network analysis. Following the initial analyses, we developed potential subtypes and prognostic models for MM using consensus clustering and lasso regression analysis. Additionally, we conducted a correlation analysis to explore the relationship between clinical features and risk scores. Finally, we constructed a weighted gene co-expression network analysis (WGCNA) and identified differentially expressed genes (DEGs) within the MM cohort.

Results

We discovered that 153 NK cell-related genes were significantly associated with the prognosisof MM patients (P <0.05). Patients in NK cluster A exhibited poorer survival outcomes compared to those in cluster B. Furthermore, our NK cell-related genes risk model revealed that patients with a high risk score had significantly worse prognoses (P <0.05). Patients with a high risk score were more likely to exhibit adverse clinical markers. Additionally, the nomogram based on NK cell-related genes demonstrated strong prognostic performance. The enrichment analysis indicated that immune-related pathways were significantly correlated with both the NK subtypes and the NK cell-related genes risk model. Ultimately, through the combined use of WGCNA and DEGs analysis, and by employing Venn diagrams, we determined that ITM2C is an independent prognostic marker for MM patients.

Conclusion

In this study, we developed a novel model based on NK cell-related genes to stratify the prognosis of MM patients. Notably, higher expression levels of ITM2C were associated with more favorable survival outcomes in these patients.

Prophylactic treatment with Bacteroides uniformis and Bifidobacterium bifidum counteracts hepatic NK cell immune tolerance in nonalcoholic steatohepatitis induced by high fat diet

Hepatic immunity is one of the driving forces for the development of nonalcoholic steatohepatitis (NASH), and targeting gut microbiota is believed to affect the hepatic immune constitution. Here, we aimed to investigate the hepatic immunological state in NASH, with a specific emphasis on natural killer (NK) cells. In addition, we aimed to identify the contributing species that target hepatic immunity to provide new directions and support the feasibility of immunotherapy for NASH. A possible NASH population was determined by combination of long-term severe fatty liver, metabolic disorders and increased serum CK18 to detect serum immune factors and gut microbiota. NASH was induced in mice fed a high-fat diet to verify the prophylactic effect of the functional species on the immunopathology and development of NASH. Hepatic immunologic state was examined, and the effector functions of NK cells were detected. Hepatic transcriptome, proteomic, and fecal metagenome were performed. We observed a statistical increase in serum IL-10 (p < 0.001) and non-statistical decrease in interferon-γ and IL-6 in NASH population, hinting at the possibility of immune tolerance. Fecal Bacteroides uniformis and Bifidobacterium bifidum were abundant in healthy population but depleted in NASH patients. In NASH mice, hepatic CD8+T cells, macrophages, and dendritic cells were increased (p < 0.01), and NK cells were inhibited, which were identified with decreased granzyme B (p < 0.05). Bacteroides uniformis and Bifidobacterium bifidum improved hepatic pathological and metabolic cues, increased hepatic NK cells and reduced macrophages (p < 0.05). Bacteroides uniformis also restored hepatic NK cell function, which was identified as increased CD107a (p < 0.05). Transcriptional and translational profiling revealed that the functional species might restore the function of hepatic NK cells through multiple pathways, such as reduction of inhibitory molecules in NK cells. Bacteroides uniformis and Bifidobacterium bifidum are novel prophylactics for NASH that restore the impaired function of hepatic NK cells.

Pancancer Analysis Revealed the Value of RAC2 in Immunotherapy and Cancer Stem Cell

Objective

To investigate the oncogenic effect and clinical significance of RAC2 in pancarcinoma from the perspective of tumor immunity and cancer stem cell.

Methods

After in-depth mining of TCGA, GEO, UCSC, and other databases, basic information of the RAC2 gene and its expression in tumor tissues as well as the relationship between RAC2 and tumor were analyzed based on survival, mutation, immune microenvironment, tumor stemness, and enrichment analysis on related pathways.

Results

RAC2 mRNA expression was increased in most tumor tissues and was associated with their prognosis. Compared to normal tissues, the RAC2 mutation rate was higher in patients with skin melanoma, uterine sarcoma, and endometrial cancer. RAC2 had a strong relation with immune cell infiltration, immunomodulators, immunotherapy markers, cancer stem cell of THYM, and immune-related pathways.

Conclusions

This study explored the potential importance of RAC2 in the prognosis, immunotherapy, and cancer stem cell of 33 cancers, laying the foundation for mechanistic experiments and its future application in clinical practice. However, the results using bioinformatics methods could be affected by the differences in patients across databases. Thus, the present results were preliminary and required further experimental validation.

CARD11 dominant negative mutation leads to altered human Natural Killer cell homeostasis

Dominant negative mutations in CARD11 have been reported in patients with immune dysregulation, severe atopic features, and variable T cell alterations. Data on Natural killer (NK) cells from affected patients are lacking. We report on a 12-year-old boy with severe atopic dermatitis, food induced anaphylaxis and hypogammaglobulinemia harbouring a novel de novo heterozygous variant c.169G > A; p.Glu57Lys in CARD11. The dominant negative effect of this mutation was confirmed on both CD4+ and CD8+. CTLA4+Foxp3+CD4+ Tregs were severely reduced. Patient's NK cells showed reduced expression of NKp46, NKG2D and CD69. Patient's CD56bright NK cells showed in vitro impaired production of IFN-γ. Steady state pS6 levels on patient's NK cells were increased and remained elevated upon IL2 + IL12 + IL18 overnight stimulation. Overall, the effect of CARD11 mutation on mTORC1 differs between T and NK cells. These findings may explain the increased susceptibility to viral infections and the reduced immune surveillance in affected patients.

The Dual Function of RhoGDI2 in Immunity and Cancer

RhoGDI2 is a guanine nucleotide dissociation inhibitor (GDI) specific for the Rho family of small GTPases. It is highly expressed in hematopoietic cells but is also present in a large array of other cell types. RhoGDI2 has been implicated in multiple human cancers and immunity regulation, where it can display a dual role. Despite its involvement in various biological processes, we still do not have a clear understanding of its mechanistic functions. This review sheds a light on the dual opposite role of RhoGDI2 in cancer, highlights its underappreciated role in immunity and proposes ways to explain its intricate regulatory functions.

A Novel RAC2 Mutation Causing Combined Immunodeficiency

PURPOSE

Ras-related C3 botulinum toxin substrate 2 (RAC2) acts as a molecular switch and has crucial roles in cell signaling and actin dynamics. A broad spectrum of genetic RAC2 mutations can cause various types of primary immunodeficiency, with complete penetrance. Here, we report a novel heterozygous missense mutation in RAC2 with incomplete penetrance, and the associated phenotypes, in a Chinese family.

METHODS

Immunological phenotype was detected by flow cytometry. T cell receptor excision circles (TRECs) and K-deleting recombination excision circles (KRECs) were assessed by real-time quantitative PCR. Gene mutations were detected by whole-exome sequencing (WES) and confirmed by Sanger sequencing.

RESULTS

The proband was an 11-year-old girl who presented with recurrent respiratory infections, bronchiectasis, persistent Epstein-Barr virus viremia, infectious mononucleosis, encephalitis, and cutaneous human papillomavirus infections. Laboratory analyses revealed increased serum IgG and decreased IgM levels, reduced naïve CD4⁺ and CD8⁺ T cells, an inverted CD4⁺/CD8⁺ ratio, and low TREC and KREC numbers. The mutation resulted in increased production of reactive oxygen species, while impaired actin polarization in neutrophils; diminished proliferative responses, increased cytokine production and a dysregulated phenotype in T lymphocytes; as well as accelerated apoptosis and hyperactivity of AKT in HL-60 human leukemia cells. WES identified a c.44G > A mutation in RAC2 resulting in a p.G15D substitution. Despite sharing the same mutation as the proband, her father suffered from recurrent respiratory infections and bronchiectasis, and had similar immunological defects, whereas her sister was apparently healthy, other than cutaneous human papillomavirus infections, and only mild immunological defects were detected preliminarily.

CONCLUSIONS

Our findings broaden the clinical and genetic spectra of RAC2 mutations and underline the importance of RAC2 gain-of-function mutations with complete or incomplete penetrance.

Combined Immunodeficiency Caused by a Novel De Novo Gain-of-Function RAC2 Mutation

Ras-related C3 botulinum toxin substrate 2 (RAC2) is a GTPase exclusively expressed in hematopoietic cells that acts as a pivotal regulator of several aspects of cell behavior via various cellular processes. RAC2 undergoes a tightly regulated GTP-binding/GTP-hydrolysis cycle, enabling it to function as a molecular switch. Mutations in RAC2 have been identified in 18 patients with different forms of primary immunodeficiency, ranging from phagocyte defects caused by dominant negative mutations to common variable immunodeficiency resulting from autosomal recessive loss-of-function mutations, or severe combined immunodeficiency due to dominant activating gain-of-function mutations. Here, we describe an 11-year-old girl with combined immunodeficiency presenting with recurrent respiratory infections and bronchiectasis. Immunological investigations revealed low T-cell receptor excision circle/K-deleting recombination excision circles numbers, lymphopenia, and low serum immunoglobulin G. Targeted next-generation sequencing identified a novel heterozygous mutation in RAC2, c.86C > G (p.P29R), located in the highly conserved Switch I domain. The mutation resulted in enhanced reactive oxygen species production, elevated F-actin content, and increased RAC2 protein expression in neutrophils, as well as increased cytokine production and a dysregulated phenotype in T lymphocytes. Furthermore, the dominant activating RAC2 mutation led to accelerated apoptosis with augmented intracellular active caspase 3, impaired actin polarization in lymphocytes and neutrophils, and diminished RAC2 polarization in neutrophils. We present a novel RAC2 gain-of-function mutation with implications for immunodeficiency and linked to functional dysregulation, including abnormal apoptosis and cell polarization arising from altered RAC2 expression. Thus, our findings broaden the spectrum of known RAC2 mutations and their underlying mechanisms.

α-Pinene Enhances the Anticancer Activity of Natural Killer Cells via ERK/AKT Pathway

Natural killer (NK) cells are lymphocytes that can directly destroy cancer cells. When NK cells are activated, CD56 and CD107a markers are able to recognize cancer cells and release perforin and granzyme B proteins that induce apoptosis in the targeted cells. In this study, we focused on the role of phytoncides in activating NK cells and promoting anticancer effects. We tested the effects of several phytoncide compounds on NK-92mi cells and demonstrated that α-pinene treatment exhibited higher anticancer effects, as observed by the increased levels of perforin, granzyme B, CD56 and CD107a. Furthermore, α-pinene treatment in NK-92mi cells increased NK cell cytotoxicity in two different cell lines, and immunoblot assays revealed that the ERK/AKT pathway is involved in NK cell cytotoxicity in response to phytoncides. Furthermore, CT-26 colon cancer cells were allografted subcutaneously into BALB/c mice, and α-pinene treatment then inhibited allografted tumor growth. Our findings demonstrate that α-pinene activates NK cells and increases NK cell cytotoxicity, suggesting it is a potential compound for cancer immunotherapy.

Higher Incidence of B Cell Malignancies in Primary Immunodeficiencies: A Combination of Intrinsic Genomic Instability and Exocytosis Defects at the Immunological Synapse

Congenital defects of the immune system called primary immunodeficiency disorders (PID) describe a group of diseases characterized by a decrease, an absence, or a malfunction of at least one part of the immune system. As a result, PID patients are more prone to develop life-threatening complications, including cancer. PID currently include over 400 different disorders, however, the variety of PID-related cancers is narrow. We discuss here reasons for this clinical phenotype. Namely, PID can lead to cell intrinsic failure to control cell transformation, failure to activate tumor surveillance by cytotoxic cells or both. As the most frequent tumors seen among PID patients stem from faulty lymphocyte development leading to leukemia and lymphoma, we focus on the extensive genomic alterations needed to create the vast diversity of B and T lymphocytes with potential to recognize any pathogen and why defects in these processes lead to malignancies in the immunodeficient environment of PID patients. In the second part of the review, we discuss PID affecting tumor surveillance and especially membrane trafficking defects caused by altered exocytosis and regulation of the actin cytoskeleton. As an impairment of these membrane trafficking pathways often results in dysfunctional effector immune cells, tumor cell immune evasion is elevated in PID. By considering new anti-cancer treatment concepts, such as transfer of genetically engineered immune cells, restoration of anti-tumor immunity in PID patients could be an approach to complement standard therapies.

RAC2 and primary human immune deficiencies

RAC2 is a GTPase that is exclusively expressed in hematopoietic cells. Animal models have suggested important roles for RAC2 in the biology of different cell types, such as neutrophils and lymphocytes. Primary immunodeficiencies represent "experimentum naturae" and offer priceless insight on the function of the human immune system. Mutations in RAC2 have been identified in a small number of patients giving rise to different forms of primary immunodeficiencies ranging from granulocyte defects caused by dominant negative mutations to combined immunodeficiency due to dominant activating mutations. This review will focus on the clinical and immunologic phenotype of patients with germline mutations in RAC2.