A novel splice variant of FR4 predominantly expressed in CD4+CD25+ regulatory T cells

Emerging roles for folate receptor FOLR1 in signaling and cancer

Folates are B vitamins that function in one-carbon metabolism. Folate receptors are one of three major types of folate transporters. The folate receptors FOLR1 and FOLR2 are overexpressed in multiple cancers. The overexpression of FOLR1 is often associated with increased cancer progression and poor patient prognosis. There is emerging evidence that FOLR1 is involved in signaling pathways that are independent of one-carbon metabolism. Recent publications implicate a direct role of FOLR1 in three signaling pathways: JAK-STAT3, ERK1/2, and as a transcription factor. Six other signaling pathways have been proposed to include FOLR1, but these currently lack sufficient data to infer a direct signaling role for FOLR1. We discuss the data that support noncanonical roles for FOLR1, and its limitations.

A Role for Folate in Microbiome-Linked Control of Autoimmunity

The microbiome exerts considerable control over immune homeostasis and influences susceptibility to autoimmune and autoinflammatory disease (AD/AID) such as inflammatory bowel disease (IBD), multiple sclerosis (MS), type 1 diabetes (T1D), psoriasis, and uveitis. In part, this is due to direct effects of the microbiome on gastrointestinal (GI) physiology and nutrient transport, but also to indirect effects on immunoregulatory controls, including induction and stabilization of T regulatory cells (T _reg). Secreted bacterial metabolites such as short-chain fatty acids (SCFA) are under intense investigation as mediators of these effects. In contrast, folate (vitamin B9), an essential micronutrient, has attracted less attention, possibly because it exerts global physiological effects which are difficult to differentiate from specific effects on the immune system. Here, we review the role of folate in AD/AID with some emphasis on sight-threatening autoimmune uveitis. Since folate is required for the generation and maintenance of T _{reg ,} we propose that one mechanism for microbiome-based control of AD/AID is via folate-dependent induction of GI tract T _{reg ,} particularly colonic T _reg, via anergic T cells (T _an). Hence, folate supplementation has potential prophylactic and/or therapeutic benefit in AID/AD.

Regulatory T Cells in Tumor Microenvironment and Approach for Anticancer Immunotherapy

Tregs have a role in immunological tolerance and immune homeostasis by suppressing immune reactions, and its therapeutic potential is critical in autoimmune diseases and cancers. There have been multiple studies conducted on Tregs because of their roles in immune suppression and therapeutic potential. In tumor immunity, Tregs can promote the development and progression of tumors by preventing effective anti-tumor immune responses in tumor-bearing hosts. High infiltration of Tregs into tumor tissue results in poor survival in various types of cancer patients. Identifying factors specifically expressed in Tregs that affect the maintenance of stability and function of Tregs is important for understanding cancer pathogenesis and identifying therapeutic targets. Thus, manipulation of Tregs is a promising anticancer strategy, but finding markers for Treg-specific depletion and controlling these cells require fine-tuning and further research. Here, we discuss the role of Tregs in cancer and the development of Treg-targeted therapies to promote cancer immunotherapy.

Growth arrest specific 1 (Gas1) and glial cell line-derived neurotrophic factor receptor α1 (Gfrα1), two mouse oocyte glycosylphosphatidylinositol-anchored proteins, are involved in fertilisation

Recently, Juno, the oocyte receptor for Izumo1, a male immunoglobulin, was discovered. Juno is an essential glycosylphosphatidylinositol (GIP)-anchored protein. This result did not exclude the participation of other GIP-anchored proteins in this process. After bibliographic and database searches we selected five GIP-anchored proteins (Cpm, Ephrin-A4, Gas1, Gfra1 and Rgmb) as potential oocyte candidates participating in fertilisation. Western blot and immunofluorescence analyses showed that only three were present on the mouse ovulated oocyte membrane and, of these, only two were clearly involved in the fertilisation process, namely growth arrest specific 1 (Gas1) and glial cell line-derived neurotrophic factor receptor α1 (Gfrα1). This was demonstrated by evaluating oocyte fertilisability after treatment of oocytes with antibodies against the selected proteins, with their respective short interference RNA or both. Gfrα1 and Gas1 seem to be neither redundant nor synergistic. In conclusion, oocyte Gas1 and Gfrα1 are both clearly involved in fertilisation.

Location and expression of Juno in mice oocytes during maturation

Objective

Oocyte-sperm interaction is the essential step in fertilization. Juno, which has been known as Folate receptor 4, is the Izumo1 receptor expressed on the oocyte membrane. This study aims to investigate the location and expression of Juno in mice oocytes during maturation.

Methods

To confirm the stage at which Juno expression begins in the mice oocytes and its location pattern, we performed immunostaining methods. Next, we evaluated Juno mRNA expression by a half quantitative RT-PCR. Juno knockdown oocytes were generated by microinjecting siRNA into the germinal vesicle (GV) stage oocytes, and analyzed the maturation rate.

Results

Our results showed that Juno was expressed on the surface of the oocyte cytoplasmic membrane at the GV stage and it continues to be expressed at similar levels in the metaphase II (MII) stages of oocytes maturation. Interestingly, Juno is also expressed on the first polar body membrane at the MII stage. Fluorescence showing Juno expression was decreased in the oolemma of siRNA injected oocytes, but it was not completely disappearing in knock down oocytes. MII stage-rates of siRNA injected oocytes were not significantly different from sham controls.

Conclusion

Juno was expressed in oocytes at the GV stage and it continues to be expressed at similar levels in later stages of oocytes maturation. Juno accumulation in oolemma during oocyte maturation is essential for fertilization, such as membrane recognition of both gametes.

Sperm Meets Egg: The Genetics of Mammalian Fertilization

Fertilization is the culminating event of sexual reproduction, which involves the union of the sperm and egg to form a single, genetically distinct organism. Despite the fundamental role of fertilization, the basic mechanisms involved have remained poorly understood. However, these mechanisms must involve an ordered schedule of cellular recognition events between the sperm and egg to ensure successful fusion. In this article, we review recent progress in our molecular understanding of mammalian fertilization, highlighting the areas in which genetic approaches have been particularly informative and focusing especially on the roles of secreted and cell surface proteins, expressed in a sex-specific manner, that mediate sperm-egg interactions. We discuss how the sperm interacts with the female reproductive tract, zona pellucida, and the oolemma. Finally, we review recent progress made in elucidating the mechanisms that reduce polyspermy and ensure that eggs normally fuse with only a single sperm.

Imbalance of different types of CD4(+)Foxp3(+) T cells in renal transplant recipients

AIMS

To determine the number of CD4(+)CD25(-)Foxp3(+), CD4(+)CD25(+)Foxp3(+) and CD4(+)CXCR5(+)Foxp3(+) T cells in renal transplant recipients that are transplanted stable (TS), or experiencing accelerated rejection (ALR), or acute rejection (AR).

METHODS

Renal transplantation was conducted in 28 patients with end-stage renal failure (ESRF). The number of peripheral CD4(+)CD25(-)Foxp3(+), CD4(+)CD25(+)Foxp3(+), or CD4(+)CXCR5(+)Foxp3(+) T cells and the serum levels of interleukin-10 (IL-10) were measured in pre- and post-transplant patients and these results were compared to 10 healthy controls (HC). Correlation between CD4(+)CD25(+)Foxp3(+) and estimated glomerular filtration rate (eGFR), CD4(+)CD25(-)Foxp3(+) and serum creatinine (Cr) levels, or Cr and IL-10 levels in TS patients was also determined.

RESULTS

The number of CD4(+)CD25(-)Foxp3(+) T cells was significantly increased in patients with ESRF, as compared to HC. Stratification analysis demonstrated that TS patients contained greater numbers of CD4(+)CD25(+)Foxp3(+) and CD4(+)CXCR5(+)Foxp3(+) T cells, higher levels of serum IL-10, and fewer numbers of CD4(+)CD25(-)Foxp3(+) T cells than ESRF patients. In contrast, ALR and AR patients contained fewer numbers of CD4(+)CD25(+)Foxp3(+) and CD4(+)CXCR5(+)Foxp3(+) T cells, greater numbers of CD4(+)CD25(-)Foxp3(+) T cells, and lower levels of serum IL-10 than ESRF patients. In TS patients, the numbers of CD4(+)CD25(+)Foxp3(+) and CD4(+)CD25(-)Foxp3(+) T cells were positively correlated with eGFR and serum Cr levels, respectively.

CONCLUSION

An imbalance of different types of CD4(+)Foxp3(+) T cells might be involved in renal transplant rejection.

Juno is the egg Izumo receptor and is essential for mammalian fertilization

Fertilization occurs when sperm and egg recognize each other and fuse to form a new, genetically distinct organism. The molecular basis of sperm-egg recognition is unknown, but is likely to require interactions between receptor proteins displayed on their surface. Izumo1 is an essential sperm cell-surface protein, but its receptor on the egg has not been described. Here we identify folate receptor 4 (Folr4) as the receptor for Izumo1 on the mouse egg, and propose to rename it Juno. We show that the Izumo1-Juno interaction is conserved within several mammalian species, including humans. Female mice lacking Juno are infertile and Juno-deficient eggs do not fuse with normal sperm. Rapid shedding of Juno from the oolemma after fertilization suggests a mechanism for the membrane block to polyspermy, ensuring eggs normally fuse with just a single sperm. Our discovery of an essential receptor pair at the nexus of conception provides opportunities for the rational development of new fertility treatments and contraceptives.

Control of alternative splicing in immune responses: many regulators, many predictions, much still to learn

Most mammalian pre-mRNAs are alternatively spliced in a manner that alters the resulting open reading frame. Consequently, alternative pre-mRNA splicing provides an important RNA-based layer of protein regulation and cellular function. The ubiquitous nature of alternative splicing coupled with the advent of technologies that allow global interrogation of the transcriptome have led to an increasing awareness of the possibility that widespread changes in splicing patterns contribute to lymphocyte function during an immune response. Indeed, a few notable examples of alternative splicing have clearly been demonstrated to regulate T-cell responses to antigen. Moreover, several proteins key to the regulation of splicing in T cells have recently been identified. However, much remains to be done to truly identify the spectrum of genes that are regulated at the level of splicing in immune cells and to determine how many of these are controlled by currently known factors and pathways versus unknown mechanisms. Here, we describe the proteins, pathways, and mechanisms that have been shown to regulate alternative splicing in human T cells and discuss what is and is not known about the genes regulated by such factors. Finally, we highlight unifying themes with regards to the mechanisms and consequences of alternative splicing in the adaptive immune system and give our view of important directions for future studies.

A novel splice variant of folate receptor 4 predominantly expressed in regulatory T cells

BACKGROUND

Regulatory T cells (Tregs) are required for proper maintenance of immunological self-tolerance and immune homeostasis. Folate receptor 4 (FR4) is expressed at high levels in transforming growth factor-beta (TGF-β)-induced Tregs and natural Tregs. Moreover, antibody-mediated targeting of FR4 is sufficient to mediate Treg depletion.

RESULTS

In this study, we describe a novel FR4 transcript variant, FR4D3, in which exon 3 is deleted. The mRNA of FR4D3 encodes a FR4 variant truncated by 189 bp. FR4D3 was found to be predominantly expressed in CD4(+)CD25(+) Treg cells. Overexpression of FR4D3 in CD4(+)CD25(+) Treg cells in vitro stimulated proliferation, which may modulate the ability of these cells to bind and incorporate folic acid.

CONCLUSIONS

Our results suggested that high levels of FR4D3 may be critical to support the substantial proliferative capacity of Treg cells.

A pivotal role of vitamin B9 in the maintenance of regulatory T cells in vitro and in vivo

Dietary factors regulate immunological function, but the underlying mechanisms remain elusive. Here we show that vitamin B9 is a survival factor for regulatory T (Treg) cells expressing high levels of vitamin B9 receptor (folate receptor 4). In vitamin B9-reduced condition in vitro, Treg cells could be differentiated from naïve T cells but failed to survive. The impaired survival of Treg cells was associated with decreased expression of anti-apoptotic Bcl2 and independent of IL-2. In vivo depletion of dietary vitamin B9 resulted in the reduction of Treg cells in the small intestine, a site for the absorption of dietary vitamin B9. These findings provide a new link between diet and the immune system, which could maintain the immunological homeostasis in the intestine.

Targeting regulatory T cells

Cancers express tumor-associated antigens that should elicit immune response to antagonize the tumor growth, but spontaneous immune rejection of established cancer is rare, suggesting an immunosuppressive environment hindering host antitumor immunity. Among the specific and active tumor-mediated mechanisms, CD4(+)CD25(high) T regulatory cells (Treg) are important mediators of active immune evasion in cancer. In this review, we will discuss Treg subpopulations and the mechanisms of their suppressive functions. Treg depletion improves endogenous antitumor immunity and the efficacy of active immunotherapy in animal models for cancer, suggesting that inhibiting Treg function could also improve the limited successes of human cancer immunotherapy. We will also discuss specific strategies for devising effective cancer immunotherapy targeting Treg.