Blocking UBE2N abrogates oncogenic immune signaling in acute myeloid leukemia

Dysregulation of innate immune signaling pathways is implicated in various hematologic malignancies. However, these pathways have not been systematically examined in acute myeloid leukemia (AML). We report that AML hematopoietic stem and progenitor cells (HSPCs) exhibit a high frequency of dysregulated innate immune-related and inflammatory pathways, referred to as oncogenic immune signaling states. Through gene expression analyses and functional studies in human AML cell lines and patient-derived samples, we found that the ubiquitin-conjugating enzyme UBE2N is required for leukemic cell function in vitro and in vivo by maintaining oncogenic immune signaling states. It is known that the enzyme function of UBE2N can be inhibited by interfering with thioester formation between ubiquitin and the active site. We performed in silico structure-based and cellular-based screens and identified two related small-molecule inhibitors UC-764864/65 that targeted UBE2N at its active site. Using these small-molecule inhibitors as chemical probes, we further revealed the therapeutic efficacy of interfering with UBE2N function. This resulted in the blocking of ubiquitination of innate immune- and inflammatory-related substrates in human AML cell lines. Inhibition of UBE2N function disrupted oncogenic immune signaling by promoting cell death of leukemic HSPCs while sparing normal HSPCs in vitro. Moreover, baseline oncogenic immune signaling states in leukemic cells derived from discrete subsets of patients with AML exhibited a selective dependency on UBE2N function in vitro and in vivo. Our study reveals that interfering with UBE2N abrogates leukemic HSPC function and underscores the dependency of AML cells on UBE2N-dependent oncogenic immune signaling states.

Abstract 432: The Atypical Cadherin Fat1 Suppresses Mitochondrial Function to Control Vascular Smooth Muscle Cell Growth After Vascular Injury

In response to vascular injury, vascular smooth muscle cells (SMCs) undergo phenotypic switching, with enhanced cell cycle entry and migration, and loss of contractile protein expression. Previously, we found that the atypical cadherin Fat1 is upregulated in SMCs after vascular injury. In cultured SMCs, Fat1 is induced by growth factor stimulation, but limits SMC proliferation. Recently, we found that Fat1 species accumulate in SMC mitochondria and interact with critical proteins, including Complex I subunits. The factors governing and significance of mitochondrial activity during SMC response to vascular injury are unclear. We hypothesized that Fat1 controls mitochondrial activity to regulate SMC growth. In cultured SMCs, loss of Fat1 increased mitochondrial oxygen consumption rate (24.8±2.2 vs. 48.1±5.4 pMoles/min, WT vs. Fat1 knockout (KO), p<0.001, n=10), maximal respiratory capacity (35.8±3.4 vs. 55.4±5.4 pMoles/min, WT vs. KO, p<0.01, n=10), oxygen consumed for ATP production (13.1±1 vs. 27.3±3.3 pMoles/min, WT vs. KO, p=0.0005, n=10), and Complex I activity (1.0±0.04 vs.1.3±0.09 RU, WT vs. KO, p<0.034, n=10). Reactive oxygen species (ROS) also increased in Fat1 KO SMCs (1426±313 vs.1848±329 dihydroethidium fluorescence intensity/cell, WT vs. KO, p<0.002, n=3). SMCs lacking Fat1 exhibited enhanced growth (p<0.0001, n=12) and dedifferentiation; adding Rotenone to inhibit Complex I function opposed this growth advantage (p<0.0001, n=6). In a mouse model of vascular injury, SMC Fat1 deletion caused early and exuberant medial hyperplasia, (0.23±0.23 vs.7.16±1.62%, WT n=5 vs. KO n=8, p<0.003, day 3 post-injury) and neointimal expansion (0.18±0.05 vs.0.55±0.1 I/M ratio, WT n=5 vs. KO n=8, p<0.02, day 14 post-injury). We also found higher neointimal cell proliferation (7.7±2 vs. 26±7.1% of pHH3 positive nuclei, WT vs. KO, p=0.041, n=6) and ROS production in Fat1-deleted vessels after injury. In conclusion, we show that the atypical cadherin Fat1 communicates with mitochondrial Complex I to repress energy and ROS production, acting as a molecular “brake” on mitochondrial activity to suppress SMC growth after vascular injury. This novel mechanism could serve as an effective target in the treatment of hyperproliferative vascular diseases.