cIAP1/2 antagonism eliminates MHC class I-negative tumors through T cell-dependent reprogramming of mononuclear phagocytes.

Loss of major histocompatibility complex (MHC) class I and interferon-γ (IFN-γ) sensing are major causes of primary and acquired resistance to checkpoint blockade immunotherapy. Thus, additional treatment options are needed for tumors that lose expression of MHC class I. The cellular inhibitor of apoptosis proteins 1 and 2 (cIAP1/2) regulate classical and alternative nuclear factor κB (NF-κB) signaling. Induction of noncanonical NF-κB signaling with cIAP1/2 antagonists mimics costimulatory signaling, augmenting antitumor immunity. We show that induction of noncanonical NF-κB signaling induces T cell-dependent immune responses, even in ß2-microglobulin (ß2M)-deficient tumors, demonstrating that direct CD8 T cell recognition of tumor cell-expressed MHC class I is not required. Instead, T cell-produced lymphotoxin reprograms both mouse and human macrophages to be tumoricidal. In wild-type mice, but not mice incapable of antigen-specific T cell responses, cIAP1/2 antagonism reduces tumor burden by increasing phagocytosis of live tumor cells. Efficacy is augmented by combination with CD47 blockade. Thus, activation of noncanonical NF-κB stimulates a T cell-macrophage axis that curtails growth of tumors that are resistant to checkpoint blockade because of loss of MHC class I or IFN-γ sensing. These findings provide a potential mechanism for controlling checkpoint blockade refractory tumors.

ATG7 is essential for secretion of iron from ameloblasts and normal growth of murine incisors during aging.

The incisors of rodents comprise an iron-rich enamel and grow throughout adult life, making them unique models of iron metabolism and tissue homeostasis during aging. Here, we deleted Atg7 (autophagy related 7) in murine ameloblasts, i.e. the epithelial cells that produce enamel. The absence of ATG7 blocked the transport of iron from ameloblasts into the maturing enamel, leading to a white instead of yellow surface of maxillary incisors. In aging mice, lack of ATG7 was associated with the growth of ectopic incisors inside severely deformed primordial incisors. These results suggest that 2 characteristic features of rodent incisors, i.e. deposition of iron on the enamel surface and stable growth during aging, depend on autophagic activity in ameloblasts. Abbreviations: ATG5: autophagy related 5; ATG7: autophagy related 7; CMV: cytomegalovirus; Cre: Cre recombinase; CT: computed tomography; FTH1: ferritin heavy polypeptide 1; GFP: green fluorescent protein; KRT5: keratin 5; KRT14: keratin 14; LGALS3: lectin, galactose binding, soluble 3; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; NCOA4: nuclear receptor coactivator 4; NRF2: nuclear factor, erythroid 2 like 2; SQSTM1: sequestosome 1.

NCOA4-Mediated Ferritinophagy: A Potential Link to Neurodegeneration.

NCOA4 (Nuclear receptor coactivator 4) mediates the selective autophagic degradation of ferritin, the cellular cytosolic iron storage complex, thereby playing a critical role in intracellular and systemic iron homeostasis. Disruptions in iron homeostasis and autophagy are observed in several neurodegenerative disorders raising the possibility that NCOA4-mediated ferritinophagy links these two observations and may underlie, in part, the pathophysiology of neurodegeneration. Here, we review the available evidence detailing the molecular mechanisms of NCOA4-mediated ferritinophagy and recent studies examining its role in systemic iron homeostasis and erythropoiesis. We propose additional studies to examine the potential role of NCOA4 in the brain in the context of neurodegenerative diseases.

NCOA4 maintains murine erythropoiesis via cell autonomous and non-autonomous mechanisms.

Ncoa4 mediates autophagic degradation of ferritin, the cytosolic iron storage complex, to maintain intracellular iron homeostasis. Recent evidence also supports a role for Ncoa4 in systemic iron homeostasis and erythropoiesis. However, the specific contribution and temporal importance of Ncoa4-mediated ferritinophagy in regulating systemic iron homeostasis and erythropoiesis is unclear. Here, we show that Ncoa4 has a critical role in basal systemic iron homeostasis and both cell autonomous and non-autonomous roles in murine erythropoiesis. Using an inducible murine model of Ncoa4 knockout, acute systemic disruption of Ncoa4 impaired systemic iron homeostasis leading to tissue ferritin and iron accumulation, a decrease in serum iron, and anemia. Mice acutely depleted of Ncoa4 engaged the Hif2a-erythropoietin system to compensate for anemia. Mice with targeted deletion of Ncoa4 specifically in the erythroid compartment developed a pronounced anemia in the immediate postnatal stage, a mild hypochromic microcytic anemia at adult stages, and were more sensitive to hemolysis with higher requirements for the Hif2a-erythropoietin axis and extramedullary erythropoiesis during recovery. These studies demonstrate the importance of Ncoa4-mediated ferritinophagy as a regulator of systemic iron homeostasis and define the relative cell autonomous and non-autonomous contributions of Ncoa4 in supporting erythropoiesis in vivo.

Compensatory metabolic networks in pancreatic cancers upon perturbation of glutamine metabolism.

Pancreatic ductal adenocarcinoma is a notoriously difficult-to-treat cancer and patients are in need of novel therapies. We have shown previously that these tumours have altered metabolic requirements, making them highly reliant on a number of adaptations including a non-canonical glutamine (Gln) metabolic pathway and that inhibition of downstream components of Gln metabolism leads to a decrease in tumour growth. Here we test whether recently developed inhibitors of glutaminase (GLS), which mediates an early step in Gln metabolism, represent a viable therapeutic strategy. We show that despite marked early effects on in vitro proliferation caused by GLS inhibition, pancreatic cancer cells have adaptive metabolic networks that sustain proliferation in vitro and in vivo. We use an integrated metabolomic and proteomic platform to understand this adaptive response and thereby design rational combinatorial approaches. We demonstrate that pancreatic cancer metabolism is adaptive and that targeting Gln metabolism in combination with these adaptive responses may yield clinical benefits for patients.

Differential effects of inhibitors of the PI3K/mTOR pathway on the expansion and functionality of regulatory T cells.

The PI3K/mTOR pathway is commonly deregulated in cancer. mTOR inhibitors are registered for the treatment of several solid tumors and novel inhibitors are explored clinically. Notably, this pathway also plays an important role in immunoregulation. While mTOR inhibitors block cell cycle progression of conventional T cells (Tconv), they also result in the expansion of CD4(+)CD25(hi)FOXP3(+) regulatory T cells (Tregs), and this likely limits their clinical antitumor efficacy. Here, we compared the effects of dual mTOR/PI3K inhibition (using BEZ235) to single PI3K (using BKM120) or mTOR inhibition (using rapamycin and everolimus) on Treg expansion and functionality. Whereas rapamycin, everolimus and BEZ235 effected a relative expansion benefit for Tregs and increased their overall suppressive activity, BKM120 allowed for similar expansion rates of Tregs and Tconv without altering their overall suppressive activity. Therefore, PI3K inhibition alone might offer antitumor efficacy without the detrimental selective expansion of Tregs associated with mTOR inhibition.

VEGF-Induced Expression of miR-17-92 Cluster in Endothelial Cells Is Mediated by ERK/ELK1 Activation and Regulates Angiogenesis.

RATIONALE: Several lines of evidence indicate that the regulation of microRNA (miRNA) levels by different stimuli may contribute to the modulation of stimulus-induced responses. The miR-17-92 cluster has been linked to tumor development and angiogenesis, but its role in vascular endothelial growth factor-induced endothelial cell (EC) functions is unclear and its regulation is unknown. OBJECTIVE: The purpose of this study was to elucidate the mechanism by which VEGF regulates the expression of miR-17-92 cluster in ECs and determine its contribution to the regulation of endothelial angiogenic functions, both in vitro and in vivo. This was done by analyzing the effect of postnatal inactivation of miR-17-92 cluster in the endothelium (miR-17-92 iEC-KO mice) on developmental retinal angiogenesis, VEGF-induced ear angiogenesis, and tumor angiogenesis. METHODS AND RESULTS: Here, we show that Erk/Elk1 activation on VEGF stimulation of ECs is responsible for Elk-1-mediated transcription activation (chromatin immunoprecipitation analysis) of the miR-17-92 cluster. Furthermore, we demonstrate that VEGF-mediated upregulation of the miR-17-92 cluster in vitro is necessary for EC proliferation and angiogenic sprouting. Finally, we provide genetic evidence that miR-17-92 iEC-KO mice have blunted physiological retinal angiogenesis during development and diminished VEGF-induced ear angiogenesis and tumor angiogenesis. Computational analysis and rescue experiments show that PTEN (phosphatase and tensin homolog) is a target of the miR-17-92 cluster and is a crucial mediator of miR-17-92-induced EC proliferation. However, the angiogenic transcriptional program is reduced when miR-17-92 is inhibited. CONCLUSIONS: Taken together, our results indicate that VEGF-induced miR-17-92 cluster expression contributes to the angiogenic switch of ECs and participates in the regulation of angiogenesis.