Regeneration and tolerance factor is expressed during T-lymphocyte activation and plays a role in apoptosis

The Vacuolar ATPase a2-subunit regulates Notch signaling in triple-negative breast cancer cells

Triple Negative Breast Cancer (TNBC) is a subtype of breast cancer with poor prognosis for which no targeted therapies are currently available. Notch signaling has been implicated in breast cancer but the factors that control Notch in TNBC are unknown. Because the Vacuolar ATPase has been shown to be important in breast cancer invasiveness, we investigated the role of a2-subunit isoform of Vacuolar ATPase (a2V) in regulating Notch signaling in TNBC. Confocal microscopy revealed that among all the ‘a’ subunit isoforms, a2V was uniquely expressed on the plasma membrane of breast cancer cells. Both a2V and NOTCH1 were elevated in TNBC tumors tissues and cell lines. a2V knockdown by siRNA as well as V-ATPase inhibition by Bafilomycin A1 (Baf A1) in TNBC cell lines enhanced Notch signaling by increasing the expression of Notch1 intracellular Domain (N1ICD). V-ATPase inhibition blocked NICD degradation by disrupting autophagy and lysosomal acidification as demonstrated by accumulation of LC3B and diminished expression of LAMP1 respectively. Importantly, treatment with Baf A1 or anti-a2V, a novel-neutralizing antibody against a2V hindered cell migration of TNBC cells. Our findings indicate that a2V regulates Notch signaling through its role in endolysosomal acidification and emerges as a potential target for TNBC.

Male fertility and apoptosis in normal spermatogenesis are regulated by vacuolar-ATPase isoform a2

The a2 isoform of vacuolar-ATPase (ATP6V0A2, referred to as a2V) is required for normal spermatogenesis and maturation of sperm. Treatment of male mice with anti-a2V disturbs the testicular cytokine/chemokine balance and leads to severe deficiencies of spermatogenesis. The aim of the present study was to investigate the role of a2V in male fertility and in the regulation of apoptotic pathways required for normal spermatogenesis in mice. To study the role of a2V single dose of anti-a2V monoclonal antibody or mouse IgG isotype (3μg/animal) was injected i.p. into males on alternate days for 10 days. The expression of sperm maturation-related molecules and pro-apoptotic molecules was measured by real-time PCR or immunohistochemistry in control and anti-a2V-treated testes. The caspase levels and their activity were measured by western blot and fluorometry. We found that the expression of the sperm maturation-related molecules SPAM1, ADAM1, and ADAM2 was significantly decreased in testes from anti-a2V-treated males. The expression of pro-apoptotic molecules (Bax, p53, and p21) and molecules involved in the intrinsic pathway of apoptosis (caspase-9, caspase-3, and PARP), which are crucial for normal spermatogenesis was significantly reduced in testes from anti-a2V-treated males compared with the control. The total ATP level was significantly lower in anti-a2V-treated testes. The data provide novel evidence showing that a2V can regulate the apoptotic pathways, an essential testicular feature, and is necessary for efficient spermatogenesis.

T CD3+CD8+ lymphocytes are more susceptible for apoptosis in the first trimester of normal human pregnancy

Aims. Normal human pregnancy is a complex process of many immunoregulatory mechanisms which protect fetus from the activation of the maternal immune system. The aim of the study was to investigate the apoptosis of lymphocytes in peripheral blood of normal pregnant patients and healthy nonpregnant women. Methods. Sixty pregnant women and 17 nonpregnant women were included in the study. Lymphocytes were isolated and labeled with anti-CD3, anti-CD4, and anti-CD8 monoclonal antibodies. Apoptosis was detected by CMXRos staining and analyzed using the flow cytometric method. Results. We found significantly higher apoptosis of total lymphocytes in peripheral blood of pregnant patients when compared to healthy nonpregnant women. The percentage of apoptotic T CD3⁺CD8⁺ cells in the first trimester was significantly higher when compared to the third trimester of normal pregnancy. The ratio of T CD3⁺CD4⁺ : T CD3⁺CD8⁺ apoptotic lymphocytes was significantly lower in the first trimester when compared to other trimesters of pregnancy and to both of the phases of the menstrual cycle. Conclusions. The higher apoptosis of T CD3⁺CD8⁺ lymphocytes and the lower ratio of T CD3⁺CD4⁺ : T CD3⁺CD8⁺ apoptotic cells in the first trimester of normal pregnancy may suggest a higher susceptibility of T CD3⁺CD8⁺ cells for apoptosis as a protective mechanism at the early stage of pregnancy.

Regulation of apoptosis and innate immune stimuli in inflammation-induced preterm labor

An innate immune response is required for successful implantation and placentation. This is regulated, in part, by the a2 isoform of V-ATPase (a2V) and the concurrent infiltration of M1 (inflammatory) and M2 (anti-inflammatory) macrophages to the uterus and placenta. The objective of the present study was to identify the role of a2V during inflammation-induced preterm labor in mice and its relationship to the regulation of apoptosis and innate immune responses. Using a mouse model of infection-induced preterm delivery, gestational tissues were collected 8 h after intrauterine inoculation on day 14.5 of pregnancy with either saline or peptidoglycan (PGN; a TLR 2 agonist) and polyinosinic-polycytidylic acid [poly(I:C); a TLR3 agonist], modeling Gram-positive bacterial and viral infections, respectively. Expression of a2V decreased significantly in the placenta, uterus, and fetal membranes during PGN+poly(I:C)-induced preterm labor. Expression of inducible NO synthase was significantly upregulated in PGN+poly(I:C)-treated placenta and uterus. PGN+poly(I:C) treatment disturbed adherens junction proteins and increased apoptotic cell death via an extrinsic pathway of apoptosis among uterine decidual cells and spongiotrophoblasts. F4/80(+) macrophages were increased and polarization was skewed in PGN+poly(I:C)-treated uterus toward double-positive CD11c(+) (M1) and CD206(+) (M2) cells, which are critical for the clearance of dying cells and rapid resolution of inflammation. Expression of Nlrp3 and activation of caspase-1 were increased in PGN+poly(I:C)-treated uterus, which could induce pyroptosis. These results suggest that the double hit of PGN+poly(I:C) induces preterm labor via reduction of a2V expression and simultaneous activation of apoptosis and inflammatory processes.

Abortion-prone mating influences alteration of systemic a2 vacuolar ATPase expression in spleen and blood immune cells

PROBLEM

a2 isoform of vacuolar ATPase (Atp6v0a2) is important for maintaining the delicate immunological balance required for successful pregnancy. The objective of this investigation is to study the dynamic changes in spleen and blood that appear during spontaneous abortion in mice.

METHOD OF STUDY

Atp6v0a2 was measured in multiple immune cell populations from spleen and blood recovered from non-abortion-prone and abortion-prone mating combinations.

RESULTS

Atp6v0a2 expression was significantly lower (P ≤ 0.01) in the spleen recovered from abortion-prone ♀CBA × ♂DBA mating on days 12 and 16 of pregnancy when compared to non-abortion-prone ♀BALB/c × ♂BALB/c and ♀CBA × ♂BALB/c matings. Flow cytometric studies showed that significantly decreased expression of Atp6v0a2 in splenic CD4(+), CD8(+), CD19(+), and CD14(+) cells directly correlated with the high percentages of fetal resorption observed in abortion-prone mating on days 12 and 16 of pregnancy. In blood, CD4(+), CD8(+), and CD19(+) cells had a significantly reduced expression of Atp6v0a2 in abortion-prone mating compared to the non-abortion-prone mating combinations only on day 12.

CONCLUSION

This deceased expression of Atp6v0a2 in the various immune cell populations of the spleen and blood suggests that the maternal environment is not supportive to fetus and leads to poor pregnancy outcome in the abortion-prone mating model.

Novel role for the N-terminus domain of the a2 isoform of vacuolar ATPase in interleukin-1beta production

Interleukin-1beta (IL-1beta) is a mediator cytokine that is released by macrophages and epithelial cells in pregnancy and tumorigenesis before antigen recognition. a2V-ATPase is a protein expressed during pregnancy and tumorigenesis and has a novel role in immune regulation. It is expressed as a 70 kDa molecule in intracellular vesicles. Upon cell stimulation it migrates to the surface followed by the cleavage of a 20 kDa portion (a2 N-terminus domain, a2NTD). This study aimed to determine whether a2NTD could induce IL-1beta production in immune cells. Peripheral blood mononuclear cells (PMBC) were stimulated with a2NTD and analyzed for cytokine gene expression by gene arrays. Supernatants were analyzed for IL-1beta by enzyme-linked immunosorbent assay, and cells were analyzed for intracellular expression of IL-1alpha, IL-1beta, and TNF-alpha by flow cytometry. When PBMC were cultured with a2NTD, there was a 2.5-fold increase in IL1A and IL1B gene expression and no induction of TNF gene expression. There was a 72-fold increase in IL-1beta in supernatants of PBMC cultured with a2NTD. Finally, there was a 204-fold increase in intracellular expression of IL-1beta in monocytes incubated with a2NTD. These results indicate a regulatory role for a2NTD in IL-1 cytokine production and suggest a unique role for this molecule in inflammation.

The role of P2X₇ in pain and inflammation

The P2X₇ purinoceptor is unique amongst the P2X receptor family in that its activation is able to stimulate the release of mature, biologically active interleukin-1β (IL-1β), as well as a variety of other proinflammatory cytokines. Coupled with the predominate localisation of this receptor to immunocytes of haemopoetic origin, this receptor is an obvious candidate to play a major and pivotal role in processes of pain and inflammation. Using genetically modified animals that lack the P2X₇ receptor, several investigators have shown that these mice do indeed demonstrate a blunted inflammatory response, and fail to develop pain following both inflammatory and neuropathic insult. These animals also show altered cytokine production in response to inflammatory stimulus, which is far broader than merely modulation of IL-1β release. In this short article, we review the role of the P2X₇ receptor in modulating the release of cytokines and other mediators, and discuss the findings made from P2X₇ receptor-deficient animals. As well as highlighting outstanding questions regarding this intriguing receptor, we also speculate as to the potential therapeutic benefit of P2X₇ receptor modulation.

Regeneration and tolerance factor prevents bystander T-cell death associated with human immunodeficiency virus infection

Human immunodeficiency virus (HIV) infection is characterized by a depletion of T cells. This depletion is caused both by the virus-induced death of infected T cells and by the death of uninfected cells (bystander depletion) by a mechanism which is largely uncharacterized. Regeneration and tolerance factor (RTF) is a subunit of the vacuolar ATPase and a protein that is involved with activation and apoptosis. Anti-RTF antibodies mediate apoptosis in T lymphocytes. When anti-RTF was added to lymphocytes from an HIV-positive individual, they underwent larger amounts of apoptosis than cells taken from healthy controls. When lymphocytes were examined by Western blotting, those from HIV-positive individuals exhibited increased levels of expression of the 50-kDa protein (P < 0.001). A 70-kDa protein was the predominant form of RTF in uninfected control lymphocytes, being expressed in 100% of individuals studied. The expression of the 50-kDa protein in HIV-positive individuals correlated with decreased absolute CD4 counts with a sensitivity of 92% and a positive predictive value of 86%. When uninfected lymphocytes were stimulated with anti-CD3 and anti-CD28, no RTF was detected during early stimulation but a 50-kDa protein was expressed during late stimulation. When the susceptibilities of the lymphocytes to anti-RTF-induced apoptosis were measured, they correlated with the size of the RTF protein expressed. The cells were not susceptible to apoptosis when the 70-kDa RTF was present but were susceptible when the 50-kDa RTF was present. We propose that the increase in the levels of the 50-kDa RTF on cells from HIV-positive individuals is important in preventing the cell from undergoing apoptosis.

Regeneration and tolerance factor modulates the effect of adenosine triphosphate-induced interleukin 1 beta secretion in human macrophages

These studies characterize a molecule known as regeneration and tolerance factor (RTF), which controls inflammation by regulating interleukin 1 beta (IL-1 beta) secretion. Recently, it has been demonstrated that the interaction of adenosine triphosphate (ATP) with the P2X7 purinoceptor induces the secretion of IL-1 beta and initiates the inflammatory response. In these experiments, that the addition of ATP to macrophages was found to induce P2X7 activation and secretion of IL-1 beta. This secretion is enhanced with anti-RTF antibody in combination with exogenous ATP (p< 0.005). RTF is also revealed to be able to influence surface ATPase activity and, increase PI incorporation, which is an indicator of P2X7 activation. We demonstrate that RTF has a role in controlling IL-1 beta secretion by regulating P2X7 activity.

The Placental Immunomodulatory Cytokine Regeneration and Tolerance Factor is also Expressed by Both Human Cycling and Early Pregnant Endometrium

PROBLEM

Regeneration and tolerance factor (RTF) has been recently suggested to contribute to the control of fetal-ablating immunity at the maternal-fetal interface through the induction of T helper 2 (Th2)-dominated response. The protein consists of a membrane-associated domain and an extracellular portion which is proteolitically cleaved to yield a soluble peptide. In humans, it has been shown to be expressed by invading cytotrophoblasts and decidual lymphoid cells, to be increased on peripheral blood B lymphocytes during a normal gestation and on circulating natural killer cells during unsuccessful pregnancies. However, the expression of RTF in other cell types and, specifically, in non-hematopoietic maternal cells of the human uterus has not been characterized in detail. Thus, we have specifically studied the expression and modulation of the cytokine in human endometrium obtained in different phases of the cycle and in early pregnancy.

METHODS

The 20 kDa extracellular domain of RTF has been localized by immunohistochemical method and Western blot analysis. Levels of RTF messenger RNA (mRNA) in basal and stimulated conditions have been evaluated by semiquantitative reverse transcription-polymerase chain reaction.

RESULTS

The extracellular domain of RTF could be detected in both the glandular epithelium and stroma with diffuse distribution in both cycling endometrium and first trimester decidua. Both cycling and pregnant endometrium expressed the gene for RTF but mRNA levels resulted significantly increased in secretory phase-endometrial stromal cells when compared to proliferative phase samples. Inflammatory cytokines, interleukin-1beta and tumour necrosis factor alpha were able to directly increase endometrial RTF mRNA expression.

CONCLUSION

These results indicate that RTF is constitutively expressed at endometrial and decidual level and its up-regulation during the secretory phase of the cycle may be relevant in mediating some immune-related aspects of uterine physiology.