Allie H. Grossmann

Interleukin receptor activates a MYD88–ARNO–ARF6 cascade to disrupt vascular stability

The innate immune response is essential for combating infectious disease. Macrophages and other cells respond to infection by releasing cytokines, such as interleukin-1β (IL-1β), which in turn activate a well-described, myeloid-differentiation factor 88 (MYD88)-mediated, nuclear factor-κB (NF-κB)-dependent transcriptional pathway that results in inflammatory-cell activation and recruitment. Endothelial cells, which usually serve as a barrier to the movement of inflammatory cells out of the blood and into tissue, are also critical mediators of the inflammatory response. Paradoxically, the cytokines vital to a successful immune defence also have disruptive effects on endothelial cell–cell interactions and can trigger degradation of barrier function and dissociation of tissue architecture. The mechanism of this barrier dissolution and its relationship to the canonical NF-κB pathway remain poorly defined. Here we show that the direct, immediate and disruptive effects of IL-1β on endothelial stability in a human in vitro cell model are NF-κB independent and are instead the result of signalling through the small GTPase ADP-ribosylation factor 6 (ARF6) and its activator ARF nucleotide binding site opener (ARNO; also known as CYTH2). Moreover, we show that ARNO binds directly to the adaptor protein MYD88, and thus propose MYD88–ARNO–ARF6 as a proximal IL-1β signalling pathway distinct from that mediated by NF-κB. Finally, we show that SecinH3, an inhibitor of ARF guanine nucleotide-exchange factors such as ARNO, enhances vascular stability and significantly improves outcomes in animal models of inflammatory arthritis and acute inflammation.

The Small GTPase ARF6 Stimulates β-Catenin Transcriptional Activity During WNT5A-Mediated Melanoma Invasion and Metastasis

WNT5A activates ARF6 to liberate β-catenin from adherens junctions, thereby increasing the amount that can mediate gene transcription. Releasing β-Catenin for Melanoma Metastasis Signaling through the Wnt pathway stimulates gene transcription mediated by β-catenin, and nuclear β-catenin is associated with a poor prognosis in cancer. The amount of β-catenin that is available to transcriptionally activate Wnt target genes may depend on the amount that is bound by cadherin in cell-cell adhesion structures called adherens junctions. Grossmann et al. found that WNT5A, which was produced by various melanoma cell lines, activated the small guanosine triphosphatase ARF6, triggered the release of β-catenin from N-cadherin, and increased the transcriptional activity of β-catenin. Pharmacological inhibition of ARF6 reduced β-catenin activity and invasive activity of melanoma cells in culture and decreased pulmonary metastasis in mice with tumors formed from melanoma cells. Thus, ARF6 may be a viable therapeutic target for reducing the invasiveness and metastasis of melanomas. β-Catenin has a dual function in cells: fortifying cadherin-based adhesion at the plasma membrane and activating transcription in the nucleus. We found that in melanoma cells, WNT5A stimulated the disruption of N-cadherin and β-catenin complexes by activating the guanosine triphosphatase adenosine diphosphate ribosylation factor 6 (ARF6). Binding of WNT5A to the Frizzled 4–LRP6 (low-density lipoprotein receptor–related protein 6) receptor complex activated ARF6, which liberated β-catenin from N-cadherin, thus increasing the pool of free β-catenin, enhancing β-catenin–mediated transcription, and stimulating invasion. In contrast to WNT5A, the guidance cue SLIT2 and its receptor ROBO1 inhibited ARF6 activation and, accordingly, stabilized the interaction of N-cadherin with β-catenin and reduced transcription and invasion. Thus, ARF6 integrated competing signals in melanoma cells, thereby enabling plasticity in the response to external cues. Moreover, small-molecule inhibition of ARF6 stabilized adherens junctions, blocked β-catenin signaling and invasiveness of melanoma cells in culture, and reduced spontaneous pulmonary metastasis in mice, suggesting that targeting ARF6 may provide a means of inhibiting WNT/β-catenin signaling in cancer.

Mutations in 2 distinct genetic pathways result in cerebral cavernous malformations in mice

Cerebral cavernous malformations (CCMs) are a common type of vascular malformation in the brain that are a major cause of hemorrhagic stroke. This condition has been independently linked to 3 separate genes: Krev1 interaction trapped (KRIT1), Cerebral cavernous malformation 2 (CCM2), and Programmed cell death 10 (PDCD10). Despite the commonality in disease pathology caused by mutations in these 3 genes, we found that the loss of Pdcd10 results in significantly different developmental, cell biological, and signaling phenotypes from those seen in the absence of Ccm2 and Krit1. PDCD10 bound to germinal center kinase III (GCKIII) family members, a subset of serine-threonine kinases, and facilitated lumen formation by endothelial cells both in vivo and in vitro. These findings suggest that CCM may be a common tissue manifestation of distinct mechanistic pathways. Nevertheless, loss of heterozygosity (LOH) for either Pdcd10 or Ccm2 resulted in CCMs in mice. The murine phenotype induced by loss of either protein reproduced all of the key clinical features observed in human patients with CCM, as determined by direct comparison with genotype-specific human surgical specimens. These results suggest that CCM may be more effectively treated by directing therapies based on the underlying genetic mutation rather than treating the condition as a single clinical entity.

Strategy for identifying repurposed drugs for the treatment of cerebral cavernous malformation.

Background— Cerebral cavernous malformation (CCM) is a hemorrhagic stroke disease affecting up to 0.5% of North Americans that has no approved nonsurgical treatment. A subset of patients have a hereditary form of the disease due primarily to loss-of-function mutations in KRIT1, CCM2, or PDCD10. We sought to identify known drugs that could be repurposed to treat CCM. Methods and Results— We developed an unbiased screening platform based on both cellular and animal models of loss of function of CCM2. Our discovery strategy consisted of 4 steps: an automated immunofluorescence and machine-learning–based primary screen of structural phenotypes in human endothelial cells deficient in CCM2, a secondary screen of functional changes in endothelial stability in these same cells, a rapid in vivo tertiary screen of dermal microvascular leak in mice lacking endothelial Ccm2, and finally a quaternary screen of CCM lesion burden in these same mice. We screened 2100 known drugs and bioactive compounds and identified 2 candidates, cholecalciferol (vitamin D3) and tempol (a scavenger of superoxide), for further study. Each drug decreased lesion burden in a mouse model of CCM vascular disease by ≈50%. Conclusions— By identifying known drugs as potential therapeutics for CCM, we have decreased the time, cost, and risk of bringing treatments to patients. Each drug also prompts additional exploration of biomarkers of CCM disease. We further suggest that the structure-function screening platform presented here may be adapted and scaled to facilitate drug discovery for diverse loss-of-function genetic vascular disease.

Severe Liver and Skin Toxicity After Radiation and Vemurafenib in Metastatic Melanoma

Case Report A 15-year-old girl underwent wide local excision and sentinel lymphadenectomy of a thin, nonulcerated melanoma. One of 16 lymph nodes contained a focus of microscopic metastasis. Staging imaging showed no other disease. After the first of 12 planned months of adjuvant interferon alfa, the medication was discontinued early because of significant fatigue. New lung nodules were detected on surveillance computed tomography (CT) imaging 3 years after diagnosis, and a biopsy confirmed melanoma. Magnetic resonance imaging (MRI) of the brain also showed a new metastasis to the right parietal bone. The patient was started on high-dose interleukin-2. Follow-up MRI showed local progression of the skull lesion, so stereotactic radiation (RT) involving 25 Gy over five treatments was given after her second interleukin-2 cycle. Adverse effects of RT included alopecia and faint erythema in the radiated area. The patient developed back pain, and surveillance CT scans 2 weeks later showed new bone metastases in the axial skeleton, liver and spleen metastases, and progression in her lungs. BRAF mutation testing of a subcutaneous metastasis that was excised from the back showed a V600E mutation. The patient was enrolled onto a phase II study investigating vemurafenib in metastatic melanoma that was approved by the institutional review board of the University of California, Los Angeles. Her initial vemurafenib dose was 960 mg twice per day. Within 14 days, her performance status improved, with a substantial decrease in her spinal pain. No photosensitivity was observed. After 1 month, CT scans showed progression of bone metastases, but the disease in her liver, lungs, and spleen was either stable or decreased. After withholding vemurafenib for 4 days, 20 Gy of RT was administered over five fractions to the painful bone metastases. A posterior-anterior (PA) beam was used for T1 to T7 and T10 to L1, and her bilateral acetabula were treated with an AP/PA arrangement. Vemurafenib was restarted 2 days after the completion of RT. Two weeks after RT, the patient developed a tender, raised rash with well-delineated borders that matched her RT portals (Fig 1, portals are indicated in yellow; Fig 2, portals are indicated in cyan). Dry desquamation and then resolution of the skin changes occurred within 4 weeks. Imaging performed 3 weeks after RT showed overall stability of non-CNS disease, but 12 new brain metastases were detected. Although whole-brain therapy would be standard treatment in this scenario, because of significant concerns about skin toxicity, stereotactic radiosurgery (SRS) to each brain metastasis was recommended. Two weeks later the patient developed lower extremity weakness, and a lumbar spine MRI showed cauda equina compression at L4. She received 8 Gy of RT to L2 to L5 using a PA field, but vemurafenib was only withheld for 2 days because of the emergent nature of the treatment. Three days later, 20-Gy SRS was performed on each of the brain metastases. Vemurafenib was restarted 4 days after SRS, beginning at 480 mg for 3 days before moving to a full dose. Approximately 1 week after RT, she developed only mild erythema that matched the L2 to L5 portal. CT scans performed 10 weeks after the completion of her second course of RT showed interval pulmonary progression, with mixed responses elsewhere. Of concern was the development of innumerable, tightly packed, hypodense lesions in the liver that matched her previous RT portal (Fig 3A, pretreatment scan, black arrows indicate examples of liver metastases outside the RT portal; Fig 3B, posttreatment scan with RT isodose overlay [100 cGy 1 Gy]). Days later the patient developed severe chest discomfort and was admitted for pain control. The following 3 days she developed worsening abdominal pain and an acute drop in hematocrit. Interval accumulation of a large subcapsular hepatic hematoma and hemoperitoneum consistent with hepatic hemorrhage were detected on CT imaging (Fig 3C, white arrows). The patient died 2 days later. An autopsy showed an enlarged liver with multicystic change that was mostly limited to the central liver. Microscopically, these cysts were hemorrhagic and lined with melanoma cells (Fig 4A, 20 magnification of subcapsular cyst lined by melanoma. Organizing clot was seen emerging through ruptured cysts, explaining the sudden drop in hematocrit. Fig 4B, 40 magnification of multiple cysts lined by melanoma [arrow]; Fig 4C, 400 magnification). The intervening liver parenchyma showed severe zone III necrosis and scattered venous thrombi that were consistent with radiation-induced liver toxicity. However, outside of the radiation field, the liver also showed zone III necrosis, although it was less severe and without venous thrombi. This was suggestive of an additional source of liver damage subsequent to the initial insult, such as global ischemia. The late-occurring ischemic injury was likely the combined result of blood loss from a ruptured hematoma found at autopsy and multiorgan failure near the time of death.

AKT1 Activation Promotes Development of Melanoma Metastases

Metastases are the major cause of melanoma-related mortality. Previous studies implicating aberrant AKT signaling in human melanoma metastases led us to evaluate the effect of activated AKT1 expression in non-metastatic BRAF(V600E)/Cdkn2a(Null) mouse melanomas in vivo. Expression of activated AKT1 resulted in highly metastatic melanomas with lung and brain metastases in 67% and 17% of our mice, respectively. Silencing of PTEN in BRAF(V600E)/Cdkn2a(Null) melanomas cooperated with activated AKT1, resulting in decreased tumor latency and the development of lung and brain metastases in nearly 80% of tumor-bearing mice. These data demonstrate that AKT1 activation is sufficient to elicit lung and brain metastases in this context and reveal that activation of AKT1 is distinct from PTEN silencing in metastatic melanoma progression. These findings advance our knowledge of the mechanisms driving melanoma metastasis and may provide valuable insights for clinical management of this disease.

Detection of Gene Rearrangements in Targeted Clinical Next-Generation Sequencing

The identification of recurrent gene rearrangements in the clinical laboratory is the cornerstone for risk stratification and treatment decisions in many malignant tumors. Studies have reported that targeted next-generation sequencing assays have the potential to identify such rearrangements; however, their utility in the clinical laboratory is unknown. We examine the sensitivity and specificity of ALK and KMT2A (MLL) rearrangement detection by next-generation sequencing in the clinical laboratory. We analyzed a series of seven ALK rearranged cancers, six KMT2A rearranged leukemias, and 77 ALK/KMT2A rearrangement-negative cancers, previously tested by fluorescence in situ hybridization (FISH). Rearrangement detection was tested using publicly available software tools, including Breakdancer, ClusterFAST, CREST, and Hydra. Using Breakdancer and ClusterFAST, we detected ALK rearrangements in seven of seven FISH-positive cases and KMT2A rearrangements in six of six FISH-positive cases. Among the 77 ALK/KMT2A FISH-negative cases, no false-positive identifications were made by Breakdancer or ClusterFAST. Further, we identified one ALK rearranged case with a noncanonical intron 16 breakpoint, which is likely to affect its response to targeted inhibitors. We report that clinically relevant chromosomal rearrangements can be detected from targeted gene panel-based next-generation sequencing with sensitivity and specificity equivalent to that of FISH while providing finer-scale information and increased efficiency for molecular oncology testing.

ARF6 Is an Actionable Node that Orchestrates Oncogenic GNAQ Signaling in Uveal Melanoma

Activating mutations in Gαq proteins, which form the α subunit of certain heterotrimeric G proteins, drive uveal melanoma oncogenesis by triggering multiple downstream signaling pathways, including PLC/PKC, Rho/Rac, and YAP. Here we show that the small GTPase ARF6 acts as a proximal node of oncogenic Gαq signaling to induce all of these downstream pathways as well as β-catenin signaling. ARF6 activates these diverse pathways through a common mechanism: the trafficking of GNAQ and β-catenin from the plasma membrane to cytoplasmic vesicles and the nucleus, respectively. Blocking ARF6 with a small-molecule inhibitor reduces uveal melanoma cell proliferation and tumorigenesis in a mouse model, confirming the functional relevance of this pathway and suggesting a therapeutic strategy for Gα-mediated diseases.

Modeling alveolar soft part sarcomagenesis in the mouse: a role for lactate in the tumor microenvironment.

Alveolar soft part sarcoma (ASPS), a deadly soft tissue malignancy with a predilection for adolescents and young adults, associates consistently with t(X;17) translocations that generate the fusion gene ASPSCR1-TFE3. We proved the oncogenic capacity of this fusion gene by driving sarcomagenesis in mice from conditional ASPSCR1-TFE3 expression. The completely penetrant tumors were indistinguishable from human ASPS by histology and gene expression. They formed preferentially in the anatomic environment highest in lactate, the cranial vault, expressed high levels of lactate importers, harbored abundant mitochondria, metabolized lactate as a metabolic substrate, and responded to the administration of exogenous lactate with tumor cell proliferation and angiogenesis. These data demonstrate lactates role as a driver of alveolar soft part sarcomagenesis.

Molecular dissection of the mechanism by which EWS/FLI expression compromises actin cytoskeletal integrity and cell adhesion in Ewing sarcoma.

Ewing sarcoma is an aggressive pediatric bone cancer. In Ewing sarcoma cells, down-regulation of focal adhesion and actin regulatory proteins disrupts cell adhesion and actin integrity. Reexpression of target proteins zyxin and α5 integrin is sufficient to restore actin cytoskeletal integrity while enhancing lung colonization in a mouse model.