The Lysosomal Calcium Channel TRPML1 Maintains Mitochondrial Fitness in NK Cells through Interorganelle Cross-Talk

Cytotoxic lymphocytes eliminate cancer cells through the release of lytic granules, a specialized form of secretory lysosomes. This compartment is part of the pleomorphic endolysosomal system and is distinguished by its highly dynamic Ca2+ signaling machinery. Several transient receptor potential (TRP) calcium channels play essential roles in endolysosomal Ca2+ signaling and ensure the proper function of these organelles. In this study, we examined the role of TRPML1 (TRP cation channel, mucolipin subfamily, member 1) in regulating the homeostasis of secretory lysosomes and their cross-talk with mitochondria in human NK cells. We found that genetic deletion of TRPML1, which localizes to lysosomes in NK cells, led to mitochondrial fragmentation with evidence of collapsed mitochondrial cristae. Consequently, TRPML1-/- NK92 (NK92ML1-/-) displayed loss of mitochondrial membrane potential, increased reactive oxygen species stress, reduced ATP production, and compromised respiratory capacity. Using sensitive organelle-specific probes, we observed that mitochondria in NK92ML1-/- cells exhibited evidence of Ca2+ overload. Moreover, pharmacological activation of the TRPML1 channel in primary NK cells resulted in upregulation of LC3-II, whereas genetic deletion impeded autophagic flux and increased accumulation of dysfunctional mitochondria. Thus, TRPML1 impacts autophagy and clearance of damaged mitochondria. Taken together, these results suggest that an intimate interorganelle communication in NK cells is orchestrated by the lysosomal Ca2+ channel TRPML1.

Mapping the chemotactic landscape in NK cells reveals subset-specific synergistic migratory responses to dual chemokine receptor ligation

BACKGROUND

Natural killer (NK) cells have a unique capability of spontaneous cytotoxicity against malignant cells and hold promise for off-the-shelf cell therapy against cancer. One of the key challenges in the field is to improve NK cell homing to solid tumors.

METHODS

To gain a deeper understanding of the cellular mechanisms regulating trafficking of NK cells into the tumor, we used high-dimensional flow cytometry, mass cytometry, and single-cell RNA-sequencing combined with functional assays, creating a comprehensive map of human NK cell migration phenotypes.

FINDINGS

We found that the chemokine receptor repertoire of peripheral blood NK cells changes in a coordinated manner becoming progressively more diversified during NK cell differentiation and correlating tightly with the migratory response of the distinct NK cell subsets. Simultaneous ligation of CXCR1/2 and CX3CR1, synergistically potentiated the migratory response of NK cells. Analysis of 9471 solid cancers from publicly available TCGA/TARGET repositories revealed dominant chemokine patterns that varied across tumor types but with no tumor group expressing ligands for more than one chemokine receptor present on mature NK cells.

INTERPRETATION

The finding that chemokine stimulation can elicit a synergistic migratory response in NK cells combined with the identified lack of naturally occurring pairs of chemokines-chemokine receptors in human cancers may explain the systematic exclusion of NK cells from the tumor microenvironment and provides a basis for engineering next-generation NK cell therapies against malignancies.

FUNDING

The Polish Ministry of Science and Higher Education, the National Science Centre, Poland, The Norwegian Cancer Society, the Norwegian Research Council, the South-Eastern Norway Regional Health Authority, The Swedish Cancer Society, the Swedish Children's Cancer Foundation, The Swedish Research Council, The Center of Excellence: Precision Immunotherapy Alliance, Knut and Alice Wallenberg Foundation and National Cancer Institute.

Adaptive single-KIR+NKG2C+ NK cells expanded from select superdonors show potent missing-self reactivity and efficiently control HLA-mismatched acute myeloid leukemia

BACKGROUND

Natural killer (NK) cells hold great promise as a source for allogeneic cell therapy against hematological malignancies, including acute myeloid leukemia (AML). Current treatments are hampered by variability in NK cell subset responses, a limitation which could be circumvented by specific expansion of highly potent single killer immunoglobulin-like receptor (KIR)⁺NKG2C⁺ adaptive NK cells to maximize missing-self reactivity.

METHODS

We developed a GMP-compliant protocol to expand adaptive NK cells from cryopreserved cells derived from select third-party superdonors, that is, donors harboring large adaptive NK cell subsets with desired KIR specificities at baseline. We studied the adaptive state of the cell product (ADAPT-NK) by flow cytometry and mass cytometry as well as cellular indexing of transcriptomes and epitopes by sequencing (CITE-Seq). We investigated the functional responses of ADAPT-NK cells against a wide range of tumor target cell lines and primary AML samples using flow cytometry and IncuCyte as well as in a mouse model of AML.

RESULTS

ADAPT-NK cells were >90% pure with a homogeneous expression of a single self-HLA specific KIR and expanded a median of 470-fold. The ADAPT-NK cells largely retained their adaptive transcriptional signature with activation of effector programs without signs of exhaustion. ADAPT-NK cells showed high degranulation capacity and efficient killing of HLA-C/KIR mismatched tumor cell lines as well as primary leukemic blasts from AML patients. Finally, the expanded adaptive NK cells had preserved robust antibody-dependent cellular cytotoxicity potential and combination of ADAPT-NK cells with an anti-CD16/IL-15/anti-CD33 tri-specific engager led to near-complete killing of resistant CD45^dim blast subtypes.

CONCLUSIONS

These preclinical data demonstrate the feasibility of off-the-shelf therapy with a non-engineered, yet highly specific, NK cell population with full missing-self recognition capability.

Remodeling of secretory lysosomes during education tunes functional potential in NK cells

Inhibitory signaling during natural killer (NK) cell education translates into increased responsiveness to activation; however, the intracellular mechanism for functional tuning by inhibitory receptors remains unclear. Secretory lysosomes are part of the acidic lysosomal compartment that mediates intracellular signalling in several cell types. Here we show that educated NK cells expressing self-MHC specific inhibitory killer cell immunoglobulin-like receptors (KIR) accumulate granzyme B in dense-core secretory lysosomes that converge close to the centrosome. This discrete morphological phenotype is independent of transcriptional programs that regulate effector function, metabolism and lysosomal biogenesis. Meanwhile, interference of signaling from acidic Ca²⁺ stores in primary NK cells reduces target-specific Ca²⁺-flux, degranulation and cytokine production. Furthermore, inhibition of PI(3,5)P₂ synthesis, or genetic silencing of the PI(3,5)P₂-regulated lysosomal Ca²⁺-channel TRPML1, leads to increased granzyme B and enhanced functional potential, thereby mimicking the educated state. These results indicate an intrinsic role for lysosomal remodeling in NK cell education.

Induction of the BIM Short Splice Variant Sensitizes Proliferating NK Cells to IL-15 Withdrawal

Adoptive transfer of allogeneic NK cells holds great promise for cancer immunotherapy. There is a variety of protocols to expand NK cells in vitro, most of which are based on stimulation with cytokines alone or in combination with feeder cells. Although IL-15 is essential for NK cell homeostasis in vivo, it is commonly used at supraphysiological levels to induce NK cell proliferation in vitro. As a result, adoptive transfer of such IL-15-addicted NK cells is associated with cellular stress because of sudden cytokine withdrawal. In this article, we describe a dose-dependent addiction to IL-15 during in vitro expansion of human NK cells, leading to caspase-3 activation and profound cell death upon IL-15 withdrawal. NK cell addiction to IL-15 was tightly linked to the BCL-2/BIM ratio, which rapidly dropped during IL-15 withdrawal. Furthermore, we observed a proliferation-dependent induction of BIM short, a highly proapoptotic splice variant of BIM in IL-15-activated NK cells. These findings shed new light on the molecular mechanisms involved in NK cell apoptosis following cytokine withdrawal and may guide future NK cell priming strategies in a cell therapy setting.

Induction of Tissue Factor Synthesis in Human Umbilical Vein Endothelial Cells Involves Protein Kinase C

Incubation of human umbilical vein endothelial cells with one of the following compounds: endotoxin, recombinant interleukin-1β, recombinant tumor necrosis factor α, allogenic lymphocyte subpopulations or phorbol ester resulted in significant induction of tissue factor synthesis. Diacylglycerol had the same effect and also enhanced synergistically the induction caused by endotoxin and interleukin-1β. Two different inhibitors of protein kinase C, H7 and sphingosine, inhibited tissue factor synthesis at concentrations which did not depress protein synthesis in general, suggesting that protein kinase C is involved in the processes leading to tissue factor synthesis. Cells down-regulated for the tissue factor response to TPA responded essentially normally to endotoxin and interleukin-1 with regard to tissue factor synthesis.

Cellular Consequences of the Initiation of Blood Coagulation

This paper reviews some of the cell biological aspects of the consequences of blood clotting initiation. These intracellular events occur in cells carrying tissue factor (TF) when its ligand, factor VIIa, is bound to the receptor-like TF surface molecules. The intracellular signaling generated by this ligand/receptor binding and some of its consequences are described and parallel experiments with factor Xa are discussed.

The role of TF as a major player in the initiation of blood coagulation has been known since the last century1,2 and is now characterized in molecular detail. Research on TF, for a long period and for obvious reasons, concentrated on its essential role as a cofactor in this process. Its importance in the development of clinical thrombosis, be it venous or arterial, has been appreciated since it was discovered that monocytes and macrophages3 and endothelial cells,4 under certain conditions, could be induced to synthesize TF. This contributed to answering the previously unresolved question about how TF got into contact with the flowing blood in the absence of any trauma. We later demonstrated that the TF induction process, in many cases, is subject to down-regulation by cAMP5,6 and that Ca2+ influx can induce the synthesis,5,6 along with a large number of other compounds.7 We also showed that protein kinase C was a mediator in at least some of these inducing pathways.8

The purification of TF in 19739 showed that TF was an integral membrane protein. By 1977 it was clear that TF likely participated in functions other than blood clotting.10 The cloning of the gene for TF11-14 suggested that, structurally, TF was a member of the Class II cytokine receptor family.15 To fulfil the criteria for being a true receptor, it also needed a specific and high-affinity ligand, which it has in factor VII. Also, to be classified as a true receptor, ligand binding should generate an intracellular signal. In 1992, we presented the first report of such a signal in the form of Ca2+ peaks. These peaks were triggered by the addition of factor VIIa to endothelial cells carrying TF on their surface as a result of exposure to interleukin 1β. These signals were characterized further16,17 and were thought to render final proof for the function of the TF receptor.

This review discusses our findings with respect to TF/factor VIIa-induced intracellular Ca2+-signaling and concludes that there is likely a two-component receptor. The more consequential question—whether this intracellular signaling leads to altered gene expression and to other phenotypic changes—is also raised. The establishment of knockout mice18–20 and efforts to solve the three-dimensional structure of this complex by x-ray diffraction21–24 are not reviewed extensively.

A novel gene mutation in the 60s loop of human coagulation factor VII – inhibition of interdomain crosstalk

A novel mutation in the factor VII gene resulting in procoagulant activity of 7.5% and antigen levels of 23% is presented. Single-stranded conformational polymorphism and DNA sequencing analysis revealed heterozygous shifts, and mutations were detected in exons 5, 7 and 8. The mutant L204P in exon 7 was novel, while the common polymorphisms, H115H and R353Q, were located in exons 5 and 8, respectively.The molecular effect of the L204P mutation was characterized using recombinant mammalian expression in Chinese hamster ovary cells. Low levels (4 ng/ml) of secreted mutant protein were found in transiently transfected cells compared to wild-type factor VII (83 ng/ml). Metabolic labeling demonstrated that the rate of mutant protein synthesis was similar to that of wild-type FVII, and the mutant protein accumulated intracellularly with no signs of increased degradation during a four-hour chase. No interaction between secreted P204 protein and immobilized soluble tissue factor was detected using surface plasmon resonance. The activation rate of recombinant mutant FVII protein was strongly reduced compared to wild-type FVII. A 9-fold reduction in the rate of FX activation was detected whereas Km was nearly the same for wild-type and the mutant. This slow rate was caused by a correspondingly lowered rate of P204 activation. A synthetic peptide sequence comprising amino acids 177−206 blocked binding of FVIIa to the TF-chip, and the subsequent factor X activation with an IC50 value of 0.5 μM in a chromogenic factor Xa assay. Additionally, evaluation of the peptide by surface plasmon resonance analysis resulted in inhibition of complex formation with an apparent Ki of 7 μM.

The epidermal growth factor receptor (EGFR) and proline rich tyrosine kinase 2 (PYK2) are involved in tissue factor dependent factor VIIa signalling in HaCaT cells

Binding of the coagulation protease factor VIIa to its receptor Tissue Factor (TF) induces intracellular signals in several cell types including HaCaT keratinocytes. TF belongs to the cytokine receptor family, but is most likely not alone in transferring the complete TF/FVIIa signal over the plasma membrane. The protease activated receptor PAR2 is involved in factor VIIa and factor Xa signal transduction. Our results indicate that the epidermal growth factor receptor (EGFR) and the proline rich tyrosine kinase 2 (PYK2) participate in TF/FVIIa signalling as formation of the TF/FVIIa complex increased the phosphorylation of these proteins. Both FVIIa protease activity and available TF were necessary for generation of the signal. Increased tyrosine phosphorylation of the EGFR was observed following TF/FVIIa complex formation on the cell surface. The EGFR kinase inhibitor tyrphostin AG1478 abrogated the TF/FVIIa-complex induced MAP kinase activation and mRNA increase of egr-1, heparin-binding EGF, and interleukin-8 following FVIIa addition. Using specific antibodies, increased phosphorylation of PYK2 tyrosine residues 402 and 580 was observed.The first site is the major autophosphorylation site and the docking site for Src family kinases. The second site is important for the kinase activity.The Src family kinase Yes and the tyrosine phosphatase SHP-2 were detected in immunoprecipitates using either antiPYK2 or anti-EGFR antibodies.Their coprecipitation with EGFR increased in the presence of FVIIa. Moreover, the coprecipitation of EGFR and PYK2 increased with FVIIa stimulation. Together, these data suggest that EGFR, PYK2, Yes, and SHP-2 are involved in transduction of the TF/FVIIa signal possibly via transactivation of the EGF receptor.

The MOC31PE immunotoxin reduces cell migration and induces gene expression and cell death in ovarian cancer cells

Background

The standard treatment of ovarian cancer with chemotherapy often leads to drug resistance and relapse of the disease, and the need for development of novel therapy alternatives is obvious. The MOC31PE immunotoxin binds to the cell surface antigen EpCAM, which is expressed by the majority of epithelial cancers including ovarian carcinomas, and we studied the cytotoxic effects of MOC31PE in ovarian cancer cells.

Methods

Investigation of the effects of MOC31PE treatment on protein synthesis, cell viability, proliferation and gene expression of the ovarian cancer cell lines B76 and HOC7.

Results

MOC31PE treatment for 24 h caused a dose-dependent reduction of protein synthesis with ID₅₀ values of less than 10 ng/ml, followed by reduced cell viability. In a gene expression array monitoring the expression of 84 key genes in cancer pathways, 13 of the genes were differentially expressed by MOC31PE treatment in comparison to untreated cells. By combining MOC31PE and the immune suppressor cyclosporin A (CsA) the MOC31PE effect on protein synthesis inhibition and cell viability increased tenfold. Cell migration was also reduced, both in the individual MOC31PE and CsA treatment, but even more when combining MOC31PE and CsA. In tumor metastasis PCR arrays, 23 of 84 genes were differentially expressed comparing CsA versus MOC31PE + CsA treatment. Increased expression of the tumor suppressor KISS1 and the nuclear receptor NR4A3 was observed, and the differential candidate gene expression was confirmed in complementary qPCR analyses. For NR4A3 this was not accompanied by increased protein expression. However, a subcellular fractionation assay revealed increased mitochondrial NR4A3 in MOC31PE treated cells, suggesting a role for this protein in MOC31PE-induced apoptotic cell death.

Conclusion

The present study demonstrates that MOC31PE may become a new targeted therapy for ovarian cancer and that the MOC31PE anti-cancer effect is potentiated by CsA.

Cellular Effects of Initiation of the Extrinsic Pathway of Blood Coagulation

In the initial phase of scientific research into blood clotting around 50 years ago, most studies focused on investigating blood samples to find out what took place in the flowing blood. With the purification and cloning of Tissue Factor (TF) it was realized that TF was an integral membrane protein sitting in the cell surface membrane. This shifted the emphasis to investigations of what happened on the cell surface, and later to the cell biology of TF and its inducibility in monocytes/macrophages and endothelial cells. During the last 8 years, researchers have become increasingly interested in studying the processes going on inside the cells that carry TF when coagulation is initiated on their surface. Cells carrying TF have been incriminated in tumorigenesis, metastasis, angiogenesis, and a number of other cellular phenotypes. That binding of the plasma clotting Factor VIIa upregulates a number of genes involved in regulation of growth, transcription, and cellular motility, as well as cytokines, makes it possible to suggest a link between the formation of the TF/Factor VIIa complex and these cellular processes.

Effects of binding of ligand (FVIIa) to induced tissue factor in human endothelial cells

The tissue factor protein is structurally related to the cytokine receptors and ligand binding (factor VIIa) has been reported to give an intracellular calcium signal, thus indicating that tissue factor is a true receptor. In view of the attempts to use recombinant factor VIIa as a therapeutic agent in hemophilia, its binding effects may be of clinical interest. We have studied the effect of ligand binding to human endothelial cells that were stimulated with interleukin-1 to express tissue factor. Human umbilical cord vein endothelial cells produce and release a wide variety of proteins that participate in coagulation and fibrinolysis, and we have investigated whether binding of recombinant factor VIIa to tissue factor altered the release of some of these compounds. Three main findings are reported. (1) After an initial increase, the measurable tissue factor activity in endothelial cells decreased more rapidly in the presence of factor VIIa (half-life 3.7+/-0.7 hours) than in its absence (half-life 7.4+/-1.5 hours). This difference was not seen when tissue factor antigen was measured, indicating that ligand binding did not increase the degradation of the protein. (2) Tissue factor pathway inhibitor was detected on the cell surface, in cell homogenates, and in cell medium. When recombinant factor VIIa was added to the cells there was a significant decrease in the release of tissue factor pathway inhibitor to the medium. Four hours after recombinant factor VIIa was added, the levels were 7.5-fold higher in the medium of untreated cells compared to the medium of cells treated with recombinant factor VIIa. (3) We observed increased release of von Willebrand factor (vWF). After 1 and 6 hours with recombinant FVIIa the release was significantly greater than in controls without FVIIa. We did not detect significant differences in the release of tissue plasminogen activator or tissue factor pathway inhibitor.

Induction of tissue factor synthesis in human umbilical vein endothelial cells involves protein kinase C

Incubation of human umbilical vein endothelial cells with one of the following compounds: endotoxin, recombinant interleukin-1 beta, recombinant tumor necrosis factor alpha, allogenic lymphocyte subpopulations or phorbol ester resulted in significant induction of tissue factor synthesis. Diacylglycerol had the same effect and also enhanced synergistically the induction caused by endotoxin and interleukin-1 beta. Two different inhibitors of protein kinase C, H7 and sphingosine, inhibited tissue factor synthesis at concentrations which did not depress protein synthesis in general, suggesting that protein kinase C is involved in the processes leading to tissue factor synthesis. Cells down-regulated for the tissue factor response to TPA responded essentially normally to endotoxin and interleukin-1 with regard to tissue factor synthesis.