Adaptive changes to oxygen availability are critical for cell survival and tissue homeostasis. Prolonged oxygen deprivation due to reduced blood flow to cardiac or peripheral tissues can lead to myocardial infarction and peripheral vascular disease, respectively. Mammalian cells respond to hypoxia by modulating oxygen-sensing transducers that stabilize the transcription factor hypoxia-inducible factor 1α (HIF-1α), which transactivates genes governing angiogenesis and metabolic pathways. Oxygen-dependent changes in HIF-1α levels are regulated by proline hydroxylation and proteasomal degradation. Here we provide evidence for what we believe is a novel mechanism regulating HIF-1α levels in isolated human ECs during hypoxia. Hypoxia differentially increased microRNA-424 (miR-424) levels in ECs. miR-424 targeted cullin 2 (CUL2), a scaffolding protein critical to the assembly of the ubiquitin ligase system, thereby stabilizing HIF-α isoforms. Hypoxia-induced miR-424 was regulated by PU.1-dependent transactivation. PU.1 levels were increased in hypoxic endothelium by RUNX-1 and C/EBPα. Furthermore, miR-424 promoted angiogenesis in vitro and in mice, which was blocked by a specific morpholino. The rodent homolog of human miR-424, mu-miR-322, was significantly upregulated in parallel with HIF-1α in experimental models of ischemia. These results suggest that miR-322/424 plays an important physiological role in post-ischemic vascular remodeling and angiogenesis.

Hypoxia-driven changes in the tumor microenvironment facilitate cancer metastasis. In the present study, we investigated the regulatory cross talk between endocytic pathway, hypoxia, and tumor metastasis. Dynamin 2 (DNM2), a GTPase, is a critical mediator of endocytosis. Hypoxia decreased the levels of DNM2. DNM2 promoter has multiple hypoxia-inducible factor (HIF)-binding sites and genetic deletion of them relieved hypoxia-induced transcriptional suppression. Interestingly, DNM2 reciprocally regulated HIF. Inhibition of DNM2 GTPase activity and dominantnegative mutant of DNM2 showed a functional role for DNM2 in regulating HIF. Furthermore, the opposite strand of DNM2 gene encodes miR-199a, which is similarly reduced in cancer cells under hypoxia. miR-199a targets the 3′-UTR of HIF-1α and HIF-2α. Decreased miR-199a expression in hypoxia increased HIF levels. Exogenous expression of miR-199a decreased HIF, cell migration, and metastasis of ovarian cancer cells. miR-199a-mediated changes in HIF levels affected expression of the matrix-remodeling enzyme, lysyloxidase (LOX). LOX levels negatively correlated with progression-free survival in ovarian cancer patients. These results demonstrate a regulatory relationship between DNM2, miR199a, and HIF, with implications in cancer metastasis.microRNA | iron regulation E pithelial ovarian cancer (EOC) is the leading cause of death among the gynecological malignancies (1). Ascites development and peritoneal metastasis are unique features of ovarian cancer progression. Gas analyses of ovarian cancer ascites show about 2.5% dissolved oxygen content, whereas the blood oxygen content ranges between 15% and 23% (2). Hypoxic areas are common in tumor microenvironment as increased metabolic demands of rapidly proliferating cells outpace oxygen availability. Sustained exposure to hypoxia spurs cells to reorganize cellular processes, and energy-consuming functions, such as endocytosis, are suppressed (3, 4). Hypoxia-inducible factor-1α and hypoxia-inducible factor-2α (HIF-1α/HIF-2α) are principal coordinators of these responses. HIF-1α/HIF-2α are stabilized in hypoxia and associate with hypoxia-inducible factor-1β (HIF-1β) to form heterodimeric transcription factors and induce the expression of target genes (5, 6). HIF-1-mediated expression of lysyloxidase (LOX) cross-links collagens and induces cell migration (7). Epithelial ovarian cancer cells (EOCCs) that have adapted to hypoxia by activating HIF-1 disseminate from primary ovarian tumors and exfoliate into the peritoneal cavity. HIF-1 significantly enhances gene signatures associated with tissue remodeling, the morbidity and mortality associated with EOC (8, 9).Regulation of HIF-1 is a key step in the hypoxic response with profound implications for EOC metastasis. Under normoxia, HIF-1α is hydroxylated within its oxygen-dependent degradation domain (ODDD) by prolylhydroxylases (PHDs). This reaction is an oxygen-, iron-, 2-oxoglutarate and ascorbate-dependent process. Hydroxylated HIF-1α is recognized and bound by a complex that...

Many intracellular signals, such as host danger-associated molecules and bacterial toxins during infection, elicit inflammasome activation. However, the mechanical environment in tissues may also influence the sensitivity of various inflammasomes to activation. The cellular mechanical environment is determined by the extracellular tissue stiffness, or its inverse, tissue compliance. Tissue stiffness is sensed by the intracellular cytoskeleton through a process termed mechanotransduction. Thus, extracellular compliance and the intracellular cytoskeleton may regulate the sensitivity of inflammasome activation. Control of proinflammatory signaling by tissue compliance may contribute to the pathogenesis of diseases such as ventilator-induced lung injury during bacterial pneumonia and tissue fibrosis in inflammatory disorders. The responsible signaling cascades in inflammasome activation pathways and mechanotransduction crosstalk are not yet fully understood. This rather different immunomodulatory perspective will be reviewed and open questions discussed here. K E Y W O R D S cell adhesion, inflammasome, inflammation, integrins, mechanobiology, monocytes/macrophages

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Immune checkpoint blockade therapy is beneficial and even curative for some cancer patients. However, the majority don’t respond to immune therapy. Across different tumor types, pre-existing T cell infiltrates predict response to checkpoint-based immunotherapy. Based on in vitro pharmacological studies, mouse models and analyses of human melanoma patients, we show that the cytokine GDF-15 impairs LFA-1/β2-integrin-mediated adhesion of T cells to activated endothelial cells, which is a pre-requisite of T cell extravasation. In melanoma patients, GDF-15 serum levels strongly correlate with failure of PD-1-based immune checkpoint blockade therapy. Neutralization of GDF-15 improves both T cell trafficking and therapy efficiency in murine tumor models. Thus GDF-15, beside its known role in cancer-related anorexia and cachexia, emerges as a regulator of T cell extravasation into the tumor microenvironment, which provides an even stronger rationale for therapeutic anti-GDF-15 antibody development.