SIRT2 regulates proliferation and chemotherapy response of MLL-ENL-driven acute myeloid leukemia.

Both MLL-AF9 and MLL-ENL leukemia fusion proteins drive oncogenic transformation of hematopoietic cells through their N-terminal DNA/histone binding mixed-lineage leukemia 1 domain and C-terminal fragment of AF9 or ENL containing an unstructured linker region and the ANC1 homology domain, which recruits transcription factors. Despite of their structural similarity, acute myeloid leukemia (AML) patients bearing MLL-ENL show more adverse outcomes compared to those with MLL-AF9. We recapitulated the clinical patterns of these two MLL-fusions driven AMLs using murine models and found that MLL-ENL AML cells showed slower cell cycle progression and more resistance to standard chemotherapy than MLL-AF9 cells. These phenotypes were primarily controlled by the linker regions of ENL and a highly conserved lysine residue K469 within. Substitution of K469 with an acetylated mimic glutamine abolished the ability of MLL-ENL to suppress proliferation and promote chemo-resistance. We showed that deacetylase Sirt2 might act as an upstream regulator of MLL-ENL. Deletion of Sirt2 promoted proliferation of AML cells with either MLL fusions. Importantly, loss of Sirt2 greatly enhanced the sensitivity of the MLL-ENL AML cells to chemo-treatment. Taken together, our study uncovered a unique regulatory role of Sirt2 in leukemogenesis and suggested targeting SIRT2 as a new way to sensitize MLL-ENL AML patience for chemotherapy.

SENP3 in monocytes/macrophages up-regulates tissue factor and mediates lipopolysaccharide-induced acute lung injury by enhancing JNK phosphorylation.

The mechanisms underlying coagulation abnormalities in sepsis and septic acute lung injury remain unclear. Tissue factor (TF) initiates coagulation; its production can be regulated by reactive oxygen species (ROS); and monocytes/macrophages produce pathological TF during sepsis. The SUMO2/3 protease SENP3 is redox-sensitive, and SENP3 accumulation in lipopolysaccharide (LPS)-activated macrophages is ROS-dependent. To explore whether SENP3 contributes to LPS-activated coagulation, we used mice with Senp3 conditional knockout (cKO) in myeloid cells. In the model of LPS-induced sepsis, SENP3 cKO mice exhibited less severe acute lung injury than SENP3 fl/fl mice. SENP3 cKO mice exhibited decreased TF expression in monocytes and alveolar macrophages, with consequently compromised coagulation in their blood and lungs. In vitro results showed that ROS-induced SENP3 accumulation contributed to LPS-induced TF expression, which was reduced by JNK inhibitor SP600125. Furthermore, mice injected with LPS following SP600125 (75 mg/kg) treatment showed decreased monocytes/macrophages TF production and alleviated coagulation activation, with less severe lung injury and higher survival rates. Collectively, the results suggest that SENP3 mediates LPS-induced coagulation activation by up-regulating monocyte/macrophage TF production in a JNK-dependent manner. This work provides new insights into ROS regulation of LPS-activated coagulation and reveals a link between SUMOylation and coagulation.

DeSUMOylation of MKK7 kinase by the SUMO2/3 protease SENP3 potentiates lipopolysaccharide-induced inflammatory signaling in macrophages.

Protein SUMOylation has been reported to play a role in innate immune response, but the enzymes, substrates, and consequences of the specific inflammatory signaling events are largely unknown. Reactive oxygen species (ROS) are abundantly produced during macrophage activation and required for Toll-like receptor 4 (TLR4)-mediated inflammatory signaling. Previously, we demonstrated that SENP3 is a redox-sensitive SUMO2/3 protease. To explore any links between reversible SUMOylation and ROS-related inflammatory signaling in macrophage activation, we generated mice with Senp3 conditional knock-out in myeloid cells. In bacterial lipopolysaccharide (LPS)-induced in vitro and in vivo inflammation models, we found that SENP3 deficiency markedly compromises the activation of TLR4 inflammatory signaling and the production of proinflammatory cytokines in macrophages exposed to LPS. Moreover, Senp3 conditional knock-out mice were significantly less susceptible to septic shock. Of note, SENP3 deficiency was associated with impairment in JNK phosphorylation. We found that MKK7, which selectively phosphorylates JNK, is a SENP3 substrate and that SENP3-mediated deSUMOylation of MKK7 may favor its binding to JNK. Importantly, ROS-dependent SENP3 accumulation and MKK7 deSUMOylation rapidly occurred after LPS stimulation. In conclusion, our findings indicate that SENP3 potentiates LPS-induced TLR4 signaling via deSUMOylation of MKK7 leading to enhancement in JNK phosphorylation and the downstream events. Therefore this work provides novel mechanistic insights into redox regulation of innate immune responses.

Tumor suppressor HIC1 is synergistically compromised by cancer-associated fibroblasts and tumor cells through the IL-6/pSTAT3 axis in breast cancer.

BACKGROUND: Interleukin-6 (IL-6) is commonly highly secreted in the breast cancer (BrCA) microenvironment and implicated in disease development. In this study, we aimed to determine the role of the IL-6/pSTAT3/HIC1 axis in the breast cancer microenvironment, including in cancer-associated fibroblasts (CAFs) and breast cancer cells. METHODS: Stromal fibroblasts from the breast cancer tissue were isolated, and the supernatants of the fibroblasts were analyzed. Recombinant human IL-6 (rhIL-6) was applied to simulate the effect of CAF-derived IL-6 to study the mechanism of HIC1 (tumor suppressor hypermethylated in cancer 1) downregulation. IL-6 was knocked down in the high IL-6-expressing BrCA cell line MDA-MB-231, which enabled the investigation of the IL-6/pSTAT3/HIC1 axis in the autocrine pathway. RESULTS: Increased IL-6 was found in the supernatant of isolated CAFs, which suppressed HIC1 expression in cancer cells and promoted BrCA cell proliferation. After stimulating the BrCA cell line SK-BR-3 (where IL-6R is highly expressed) with rhIL-6, signal transducers and activators of transcription 3 (STAT3) was found to be phosphorylated and HIC1 decreased, and a STAT3 inhibitor completely rescued HIC1 expression. Moreover, HIC1 was restored upon knocking down IL-6 expression in MDA-MB-231 cells, accompanied by a decrease in STAT3 activity. CONCLUSIONS: These findings indicate that IL-6 downregulates the tumor suppressor HIC1 and promotes BrCA development in the tumor microenvironment through paracrine or autocrine signaling.

SENP3 loss promotes M2 macrophage polarization and breast cancer progression.

Tumor-associated macrophages (TAM) play a crucial role in promoting cancer progression. Upon cytokine stimulation, TAM preferentially polarize to the anti-inflammatory and pro-tumor M2 subtype. The mechanism underlying such preferential polarization remains elusive. Here, we report that macrophage-specific deletion of the SUMO-specific protease Sentrin/SUMO-specific protease 3 promotes macrophage polarization towards M2 in bone marrow-derived macrophage (BMDM) induced by interleukin 4 (IL-4)/IL-13 and in an ex vivo model (murine Py8119 cell line), as well as in a mouse orthotopic tumor model. Notably, Sentrin/SUMO-specific protease 3 (SENP3) loss in macrophages accelerated breast cancer malignancy in ex vivo and in vivo models. Mechanistically, we identified Akt Serine/threonine kinase 1 (Akt1) as the substrate of SENP3 and found that the enhanced Akt1 SUMOylation upon SENP3 loss resulted in Akt1 hyper-phosphorylation and activation, which facilitates M2 polarization. Analysis of clinical data showed that a lower level of SENP3 in TAM has a strong negative correlation with the level of the M2 marker CD206, as well as with a worse clinical outcome. Thus, increased Akt1 SUMOylation as a result of SENP3 deficiency modulates polarization of macrophages to the M2 subtype within a breast cancer microenvironment, which in turn promotes tumor progression.

Redox-sensitive enzyme SENP3 mediates vascular remodeling via de-SUMOylation of ß-catenin and regulation of its stability.

BACKGROUND: Oxidative stress plays critical pathophysiological roles in vascular remodeling-related cardiovascular diseases, including hypertension, atherosclerosis, and restenosis. Previous studies demonstrate that SENP3, a redox-sensitive SUMO2/3-specific protease, is strongly implicated in cancer development and progression. However, the role of SENP3 in vascular remodeling remains unknown. METHODS: We generated three mouse models of vascular remodeling due to low shear stress, hypertension, and atherosclerosis. The expression of SENP3 was determined by western blotting and/or immunofluorescence staining in cultured vascular smooth muscle cells (VSMCs), animal models, and human samples. The biological function of SENP3 in proliferation and migration of VSMC and vascular remodeling was further investigated in vitro and in vivo models. FINDINGS: SENP3 was highly expressed in VSMCs of remodeled arteries, accompanied by elevated reactive oxygen species (ROS) levels. In cultured VSMCs, SENP3 protein levels were enhanced by oxidized low-density lipoprotein and Angiotensin II in a ROS-dependent manner. SENP3 overexpression significantly promoted and sh-RNA-mediated knockdown markedly inhibited VSMCs proliferation and migration. Immunofluorescence staining showed that SENP3 expression was correlated with intimal area in remodeled arteries. Furthermore, we demonstrated that SENP3 interacted with ß-catenin and inhibited its proteasome-dependent degradation via de-SUMOylation of ß-catenin. Most importantly, SENP3+/- mice exhibited alleviated vascular remodeling. INTERPRETATION: Our results highlight the important function of SENP3 as a redox sensor and mediator in vascular remodeling.

SENP3 Suppresses Osteoclastogenesis by De-conjugating SUMO2/3 from IRF8 in Bone Marrow-Derived Monocytes.

Bone metabolism depends on the balance between osteoclast-driven bone resorption and osteoblast-mediated bone formation. Diseases like osteoporosis are characterized by increased bone destruction due to partially enhanced osteoclastogenesis. Here, we report that the post-translational SUMO modification is critical for regulating osteoclastogenesis. The expression of the SUMO-specific protease SENP3 is downregulated in osteoclast precursors during osteoclast differentiation. Mice with SENP3 deficiency in bone marrow-derived monocytes (BMDMs) exhibit more severe bone loss due to over-activation of osteoclasts after ovariectomy. Deleting SENP3 in BMDMs promotes osteoclast differentiation. Mechanistically, loss of SENP3 increases interferon regulatory factor 8 (IRF8) SUMO3 modification at the K310 amino acid site, which upregulates expression of the nuclear factor of activated T cell c1 (NFATc1) and osteoclastogenesis. In summary, IRF8 de-SUMO modification mediated by SENP3 suppresses osteoclast differentiation and suggests strategies to treat bone loss diseases.

A fine-tuning mechanism underlying self-control for autophagy: deSUMOylation of BECN1 by SENP3.

The roles of SUMOylation and the related enzymes in autophagic regulation are unclear. Based on our previous studies that identified the SUMO2/3-specific peptidase SENP3 as an oxidative stress-responsive molecule, we investigated the correlation between SUMOylation and macroautophagy/autophagy. We found that Senp3± mice showed increased autophagy in the liver under basal and fasting conditions, compared to Senp3+/+ mice. We constructed a liver-specific senp3 knockout mouse; these Senp3-deficient liver tissues showed increased autophagy as well. Autophagic flux was accelerated in hepatic and other cell lines following knockdown of SENP3, both before and after the cells underwent starvation in the form of the serum and amino acid deprivation. We demonstrated that BECN1/beclin 1, the core molecule of the BECN1-PIK3C3 complex, could be SUMO3-conjugated by PIAS3 predominantly at K380 and deSUMOylated by SENP3. The basal SUMOylation of BECN1 was increased upon cellular starvation, which enhanced autophagosome formation by facilitating BECN1 interaction with other complex components UVRAG, PIK3C3 and ATG14, thus promoting PIK3C3 activity. In contrast, SENP3 deSUMOylated BECN1, which impaired BECN1-PIK3C3 complex formation or stability to suppress the PIK3C3 activity. DeSUMOylation of BECN1 restrained autophagy induction under basal conditions and especially upon starvation when SENP3 had accumulated in response to the increased generation of reactive oxygen species. Thus, while reversible SUMOylation regulated the degree of autophagy, SENP3 provided an intrinsic overflow valve for fine-tuning autophagy induction. ABBREVIATIONS: AL: autolysosome; AP: autophagosome; ATG: autophagy related; ATG14: autophagy related 14; BECN1: beclin 1, autophagy related; cKO: conditional knockout; co-IP: co-immunoprecipitation; CQ: chloroquine; EBSS: Earle's balanced salt solution; GFP: green fluorescent protein; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; NAC: N-acetyl-L-cysteine; PIK3C3: phosphatidylinositol 3-kinase catalytic subunit type 3; PTM: post-translational modification; RFP: red fluorescent protein; ROS: reactive oxygen species; RUBCN/rubicon: RUN domain and cysteine-rich domain containing, BECN1-interacting protein; SENP3: SUMO specific peptidase 3; shRNA: small hairpin RNA; siRNA: small interfering RNA; SQSTM1: sequestosome 1; SUMO: small ubiquitin-like modifier; UVRAG: UV radiation resistance associated gene.

hCINAP regulates the DNA-damage response and mediates the resistance of acute myelocytic leukemia cells to therapy.

Acute myeloid leukemia (AML) is a genetically heterogeneous malignant disorder of the hematopoietic system, characterized by the accumulation of DNA-damaged immature myeloid precursors. Here, we find that hCINAP is involved in the repair of double-stranded DNA breaks (DSB) and that its expression correlates with AML prognosis. Following DSB, hCINAP is recruited to damage sites where it promotes SENP3-dependent deSUMOylation of NPM1. This in turn results in the dissociation of RAP80 from the damage site and CTIP-dependent DNA resection and homologous recombination. NPM1 SUMOylation is required for recruitment of DNA repair proteins at the early stage of DNA-damage response (DDR), and SUMOylated NPM1 impacts the assembly of the BRCA1 complex. Knockdown of hCINAP also sensitizes a patient-derived xenograft (PDX) mouse model to chemotherapy. In clinical AML samples, low hCINAP expression is associated with a higher overall survival rate in patients. These results provide mechanistic insight into the function of hCINAP during the DNA-damage response and its role in AML resistance to therapy.

SENP3 maintains the stability and function of regulatory T cells via BACH2 deSUMOylation.

Regulatory T (Treg) cells are essential for maintaining immune homeostasis and tolerance, but the mechanisms regulating the stability and function of Treg cells have not been fully elucidated. Here we show SUMO-specific protease 3 (SENP3) is a pivotal regulator of Treg cells that functions by controlling the SUMOylation and nuclear localization of BACH2. Treg cell-specific deletion of Senp3 results in T cell activation, autoimmune symptoms and enhanced antitumor T cell responses. SENP3-mediated BACH2 deSUMOylation prevents the nuclear export of BACH2, thereby repressing the genes associated with CD4+ T effector cell differentiation and stabilizing Treg cell-specific gene signatures. Notably, SENP3 accumulation triggered by reactive oxygen species (ROS) is involved in Treg cell-mediated tumor immunosuppression. Our results not only establish the role of SENP3 in the maintenance of Treg cell stability and function via BACH2 deSUMOylation but also clarify the function of SENP3 in the regulation of ROS-induced immune tolerance.