Loss of STAT3 in murine NK cells enhances NK cell-dependent tumor surveillance.

The members of the signal transducer and activator of transcription (STAT) family of transcription factors modulate the development and function of natural killer (NK) cells. NK cell-mediated tumor surveillance is particularly important in the body's defense against hematological malignancies such as leukemia. STAT3 inhibitors are currently being developed, although their potential effects on NK cells are not clear. We have investigated the function of STAT3 in NK cells with Stat3(Δ/Δ)Ncr1-iCreTg mice, whose NK cells lack STAT3. In the absence of STAT3, NK cells develop normally and in normal numbers, but display alterations in the kinetics of interferon-γ (IFN-γ) production. We report that STAT3 directly binds the IFN-γ promoter. In various in vivo models of hematological diseases, loss of STAT3 in NK cells enhances tumor surveillance. The reduced tumor burden is paralleled by increased expression of the activating receptor DNAM-1 and the lytic enzymes perforin and granzyme B. Our findings imply that STAT3 inhibitors will stimulate the cytolytic activity of NK cells against leukemia, thereby providing an additional therapeutic benefit.

Genetics of the human placenta: implications for toxicokinetics.

Exposure to chemicals and environmental pollutants among them cadmium, lead, and mercury can harm reproduction. The metals cross the placenta, accumulate in placental tissue, and pass onto fetal blood and fetal organs to variable amounts. Still, the mechanisms underlying their transplacental passage are largely unknown and the human placenta is the most poorly understood organ in terms of reproduction toxicology. The genetic factors modulating placental toxicokinetics remain unclear just as well. From a genetic perspective, three aspects, which influence capacities of the human placenta to metabolize and transport toxicants, need to be considered. These are 1/presence and interplay of two genotypes, 2/chromosomal aberrations including aneuploidies and sequence variations, and 3/epigenetics and genetic imprinting. In this review, we summarize the current state of knowledge on how genetics and epigenetics affect placental (patho)physiology and thus fetal development and health.

Elevated metallothionein expression in long-lived species mediates the influence of cadmium accumulation on aging.

Cadmium (Cd) accumulates with aging and is elevated in long-lived species. Metallothioneins (MTs), small cysteine-rich proteins involved in metal homeostasis and Cd detoxification, are known to be related to longevity. However, the relationship between Cd accumulation, the role of MTs, and aging is currently unclear. Specifically, we do not know if long-lived species evolved an efficient metal stress response by upregulating their MT levels to reduce the toxic effects of environmental pollutants, such as Cd, that accumulate over their longer life span. It is also unknown if the number of MT genes, their expression, or both protect the organisms from potentially damaging effects during aging. To address these questions, we reanalyzed several cross-species studies and obtained data on MT expression and Cd accumulation in long-lived mouse models. We confirmed a relationship between species maximum life span in captive mammals and their Cd content in liver and kidney. We found that although the number of MT genes does not affect longevity, gene expression and protein amount of specific MT paralogs are strongly related to life span in mammals. MT expression rather than gene number may influence the high Cd levels and longevity of some species. In support of this, we found that overexpression of MT-1 accelerated Cd accumulation in mice and that tissue Cd was higher in long-lived mouse strains with high MT expression. We conclude that long-lived species have evolved a more efficient stress response by upregulating the expression of MT genes in presence of Cd, which contributes to elevated tissue Cd levels.

Don't trust an(t)ybody - Pitfalls during investigation of candidate proteins for methylmercury transport at the placental interface.

While investigating placental mercury transport, we validated specificity of commercial antibodies against four candidate transporters (Large neutral amino acids transporter (LAT)1, LAT2, 4F2 cell-surface antigen heavy chain (4F2hc), and multidrug resistance-associated protein (MRP)2) by immunoblotting and small interfering RNA (siRNA)-mediated protein knockdown. An anti-4F2hc- and one anti-LAT1-antibody were specific. Another anti-LAT1-antibody reacted with LAT2. Two anti-LAT2-antibodies detected mainly albumin in placental lysates. A specific anti-MRP2-antibody hardly detected MRP2 in human placentas, contradicting published data. We recommend testing any unknown antibody by western blotting for 1/specificity for the protein of interest using e.g. siRNA knockdown and 2/cross-reactivity with albumin.

Mercury toxicokinetics of the healthy human term placenta involve amino acid transporters and ABC transporters.

BACKGROUND: The capacity of the human placenta to handle exogenous stressors is poorly understood. The heavy metal mercury is well-known to pass the placenta and to affect brain development. An active transport across the placenta has been assumed. The underlying mechanisms however are virtually unknown. OBJECTIVES: Uptake and efflux transporters (17 candidate proteins) assumed to play a key role in placental mercury transfer were examined for expression, localization and function in human primary trophoblast cells and the trophoblast-derived choriocarcinoma cell line BeWo. METHODS: To prove involvement of the transporters, we used small interfering RNA (siRNA) and exposed cells to methylmercury (MeHg). Total mercury contents of cells were analyzed by Cold vapor-atomic fluorescence spectrometry (CV-AFS). Localization of the proteins in human term placenta sections was determined via immunofluorescence microscopy. RESULTS: We found the amino acid transporter subunits L-type amino acid transporter (LAT)1 and rBAT (related to b(0,+) type amino acid transporter) as well as the efflux transporter multidrug resistance associated protein (MRP)1 to be involved in mercury kinetics of trophoblast cells (t-test P<0.05). CONCLUSION: The amino acid transporters located at the apical side of the syncytiotrophoblast (STB) manage uptake of MeHg. Mercury conjugated to glutathione (GSH) is effluxed via MRP1 localized to the basal side of the STB. The findings can well explain why mercury is transported primarily towards the fetal side.

STAT5 Is a Key Regulator in NK Cells and Acts as a Molecular Switch from Tumor Surveillance to Tumor Promotion.

UNLABELLED: Natural killer (NK) cells are tightly regulated by the JAK-STAT signaling pathway and cannot survive in the absence of STAT5. We now report that STAT5-deficient NK cells can be rescued by overexpression of BCL2. Our experiments define STAT5 as a master regulator of NK-cell proliferation and lytic functions. Although NK cells are generally responsible for killing tumor cells, the rescued STAT5-deficient NK cells promote tumor formation by producing enhanced levels of the angiogenic factor VEGFA. The importance of VEGFA produced by NK cells was verified by experiments with a conditional knockout of VEGFA in NK cells. We show that STAT5 normally represses the transcription of VEGFA in NK cells, in both mice and humans. These findings reveal that STAT5-directed therapies may have negative effects: In addition to impairing NK-cell-mediated tumor surveillance, they may even promote tumor growth by enhancing angiogenesis. SIGNIFICANCE: The importance of the immune system in effective cancer treatment is widely recognized. We show that the new signal interceptors targeting the JAK-STAT5 pathway may have dangerous side effects that must be taken into account in clinical trials: inhibiting JAK-STAT5 has the potential to promote tumor growth by enhancing NK-cell-mediated angiogenesis.

CDK8-mediated STAT1-S727 phosphorylation restrains NK cell cytotoxicity and tumor surveillance.

The transcription factor STAT1 is important in natural killer (NK) cells, which provide immediate defense against tumor and virally infected cells. We show that mutation of a single phosphorylation site (Stat1-S727A) enhances NK cell cytotoxicity against a range of tumor cells, accompanied by increased expression of perforin and granzyme B. Stat1-S727A mice display significantly delayed disease onset in NK cell-surveilled tumor models including melanoma, leukemia, and metastasizing breast cancer. Constitutive phosphorylation of S727 depends on cyclin-dependent kinase 8 (CDK8). Inhibition of CDK8-mediated STAT1-S727 phosphorylation may thus represent a therapeutic strategy for stimulating NK cell-mediated tumor surveillance.