Mint3 in bone marrow-derived cells promotes lung metastasis in breast cancer model mice

MT1-MMP as a Key Regulator of Metastasis

Membrane type1-matrix metalloproteinase (MT1-MMP) is a member of metalloproteinases that is tethered to the transmembrane. Its major function in cancer progression is to directly degrade the extracellular matrix components, which are mainly type I-III collagen or indirectly type IV collagen through the activation of MMP-2 with a cooperative function of the tissue inhibitor of metalloproteinase-2 (TIMP-2). MT1-MMP is expressed as an inactive form (zymogen) within the endoplasmic reticulum (ER) and receives truncation processing via furin for its activation. Upon the appropriate trafficking of MT1-MMP from the ER, the Golgi apparatus to the cell surface membrane, MT1-MMP exhibits proteolytic activities to the surrounding molecules such as extracellular matrix components and cell surface molecules. MT1-MMP also retains a non-proteolytic ability to activate hypoxia-inducible factor 1 alpha (HIF-1A) via factors inhibiting the HIF-1 (FIH-1)-Mint3-HIF-1 axis, resulting in the upregulation of glucose metabolism and oxygen-independent ATP production. Through various functions of MT1-MMP, cancer cells gain motility on migration/invasion, thus causing metastasis. Despite the long-time efforts spent on the development of MT1-MMP interventions, none have been accomplished yet due to the side effects caused by off-target effects. Recently, MT1-MMP-specific small molecule inhibitors or an antibody have been reported and these inhibitors could potentially be novel agents for cancer treatment.

Mint3 as a Potential Target for Cooling Down HIF-1α-Mediated Inflammation and Cancer Aggressiveness

Hypoxia-inducible factor-1α (HIF-1α) is a transcription factor that plays a crucial role in cells adapting to a low-oxygen environment by facilitating a switch from oxygen-dependent ATP production to glycolysis. Mediated by membrane type-1 matrix metalloproteinase (MT1-MMP) expression, Munc-18-1 interacting protein 3 (Mint3) binds to the factor inhibiting HIF-1 (FIH-1) and inhibits its suppressive effect, leading to HIF-1α activation. Defects in Mint3 generally lead to improved acute inflammation, which is regulated by HIF-1α and subsequent glycolysis, as well as the suppression of the proliferation and metastasis of cancer cells directly through its expression in cancer cells and indirectly through its expression in macrophages or fibroblasts associated with cancer. Mint3 in inflammatory monocytes enhances the chemotaxis into metastatic sites and the production of vascular endothelial growth factors, which leads to the expression of E-selectin at the metastatic sites and the extravasation of cancer cells. Fibroblasts express L1 cell adhesion molecules in a Mint3-dependent manner and enhance integrin-mediated cancer progression. In pancreatic cancer cells, Mint3 directly promotes cancer progression. Naphthofluorescein, a Mint3 inhibitor, can disrupt the interaction between FIH-1 and Mint3 and potently suppress Mint3-mediated inflammation, cancer progression, and metastasis without causing marked adverse effects. In this review, we will introduce the potential of Mint3 as a therapeutic target for inflammatory diseases and cancers.

Extracellular Vesicles and Transforming Growth Factor β Signaling in Cancer

Complexity in mechanisms that drive cancer development and progression is exemplified by the transforming growth factor β (TGF-β) signaling pathway, which suppresses early-stage hyperplasia, yet assists aggressive tumors to achieve metastasis. Of note, several molecules, including mRNAs, non-coding RNAs, and proteins known to be associated with the TGF-β pathway have been reported as constituents in the cargo of extracellular vesicles (EVs). EVs are secreted vesicles delimited by a lipid bilayer and play critical functions in intercellular communication, including regulation of the tumor microenvironment and cancer development. Thus, this review aims at summarizing the impact of EVs on TGF-β signaling by focusing on mechanisms by which EV cargo can influence tumorigenesis, metastatic spread, immune evasion and response to anti-cancer treatment. Moreover, we emphasize the potential of TGF-β-related molecules present in circulating EVs as useful biomarkers of prognosis, diagnosis, and prediction of response to treatment in cancer patients.

Pharmacological inhibition of Mint3 attenuates tumour growth, metastasis, and endotoxic shock

Hypoxia-inducible factor-1 (HIF-1) plays essential roles in human diseases, though its central role in oxygen homoeostasis hinders the development of direct HIF-1-targeted pharmacological approaches. Here, we surveyed small-molecule compounds that efficiently inhibit the transcriptional activity of HIF-1 without affecting body homoeostasis. We focused on Mint3, which activates HIF-1 transcriptional activity in limited types of cells, such as cancer cells and macrophages, by suppressing the factor inhibiting HIF-1 (FIH-1). We identified naphthofluorescein, which inhibited the Mint3–FIH-1 interaction in vitro and suppressed Mint3-dependent HIF-1 activity and glycolysis in cancer cells and macrophages without evidence of cytotoxicity in vitro. In vivo naphthofluorescein administration suppressed tumour growth and metastasis without adverse effects, similar to the genetic depletion of Mint3. Naphthofluorescein attenuated inflammatory cytokine production and endotoxic shock in mice. Thus, Mint3 inhibitors may present a new targeted therapeutic option for cancer and inflammatory diseases by avoiding severe adverse effects.

Sakomoto et al. identify naphthofluorescein as a mint3 inhibitor that disrupts the Mint3–FIH-1 interaction and attenuates HIF-1 activity. In vivo experiments in mice reveal a reduction in tumor growth with attenuated inflammatory cytokine production and endotoxic shock, presenting an option for targeted therapies for cancer and inflammatory diseases that avoid severe adverse effects.

Mint3 depletion-mediated glycolytic and oxidative alterations promote pyroptosis and prevent the spread of Listeria monocytogenes infection in macrophages

Listeria monocytogenes (LM) infection induces pyroptosis, a form of regulated necrosis, in host macrophages via inflammasome activation. Here, we examined the role of Mint3 in macrophages, which promotes glycolysis via hypoxia-inducible factor-1 activation, during the initiation of pyroptosis following LM infection. Our results showed that Mint3-deficient mice were more resistant to lethal listeriosis than wild-type (WT) mice. Additionally, the mutant mice showed higher levels of IL-1β/IL-18 in the peritoneal fluid during LM infection than WT mice. Moreover, ablation of Mint3 markedly increased the activation of caspase-1, maturation of gasdermin D, and pyroptosis in macrophages infected with LM in vitro, suggesting that Mint3 depletion promotes pyroptosis. Further analyses revealed that Mint3 depletion upregulates inflammasome assembly preceding pyroptosis via glycolysis reduction and reactive oxygen species production. Pharmacological inhibition of glycolysis conferred resistance to listeriosis in a Mint3-dependent manner. Moreover, Mint3-deficient mice treated with the caspase-1 inhibitor VX-765 were as susceptible to LM infection as WT mice. Taken together, these results suggest that Mint3 depletion promotes pyroptosis in host macrophages, thereby preventing the spread of LM infection. Mint3 may serve as a target for treating severe listeriosis by inducing pyroptosis in LM-infected macrophages.

Mint3 is dispensable for pancreatic and kidney functions in mice

Munc-18 interacting protein 3 (Mint3) is an activator of hypoxia-inducible factor-1 in cancer cells, macrophages, and cancer-associated fibroblasts under pathological conditions. However, exactly which cells highly express Mint3 in vivo and whether Mint3 depletion affects their physiological functions remain unclear. Here, we surveyed mouse tissues for specific expression of Mint3 by comparing Mint3 expression in wild-type and Mint3-knockout mice. Interestingly, immunohistochemical analyses revealed that Mint3 was highly expressed in islet cells of the pancreas, distal tubular epithelia of the kidney, choroid plexus ependymal cells of the cerebrum, medullary cells of the adrenal gland, and epithelial cells of the seminal gland. We also studied whether Mint3 depletion affects the physiological functions of the islets and kidneys. Mint3-knockout mice did not show any abnormalities in glucose-tolerance and urine-biochemical tests, indicating that Mint3 depletion was compensated for in these organs. Thus, loss of Mint3 might be compensated in the islets and kidneys under physiological conditions in mice.

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Specific expression of Mint3 in mouse tissues is surveyed.

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Mint3 is highly expressed in islet cells of the pancreas.

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Mint3 is highly expressed in distal tubular epithelia of the kidney.

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Mint3 KO mice do not show any abnormalities in glucose-tolerance tests.

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Mint3 KO mice do not show any abnormalities in urine-biochemical tests.

EXOSC9 depletion attenuates P-body formation, stress resistance, and tumorigenicity of cancer cells

Cancer cells adapt to various stress conditions by optimizing gene expression profiles via transcriptional and translational regulation. However, whether and how EXOSC9, a component of the RNA exosome complex, regulates adaptation to stress conditions and tumorigenicity in cancer cells remain unclear. Here, we examined the effects of EXOSC9 depletion on cancer cell growth under various stress conditions. EXOSC9 depletion attenuated growth and survival under various stress conditions in cancer cells. Interestingly, this also decreased the number of P-bodies, which are messenger ribonucleoprotein particles (mRNPs) required for stress adaptation. Meanwhile, EXOSC2/EXOSC4 depletion also attenuated P-body formation and stress resistance with decreased EXOSC9 protein. EXOSC9-mediated stress resistance and P-body formation were found to depend on the intact RNA-binding motif of this protein. Further, RNA-seq analyses identified 343 EXOSC9-target genes, among which, APOBEC3G contributed to defects in stress resistance and P-body formation in MDA-MB-231 cells. Finally, EXOSC9 also promoted xenografted tumor growth of MDA-MB-231 cells in an intact RNA-binding motif-dependent manner. Database analyses further showed that higher EXOSC9 activity, estimated based on the expression of 343 target genes, was correlated with poorer prognosis in some cancer patients. Thus, drugs targeting activity of the RNA exosome complex or EXOSC9 might be useful for cancer treatment.

Bone-marrow-derived cell-released extracellular vesicle miR-92a regulates hepatic pre-metastatic niche in lung cancer

Metastatic tumors have been shown to establish a supportive pre-metastatic niche (PMN) in distant organs, which in turn determines disseminated tumor cells' targeting of such organs. PMN is formed through the recruitment of bone-marrow-derived cells (BMDCs); however, the role of BMDCs in PMN formation is not fully understood. On the basis of RNA-seq data and bioinformatic analysis, secretion of extracellular vesicle (EV) miR-92a by BMDCs of lung cancer-bearing mice contributes to the establishment of liver PMN. Both BMDC-derived EVs and miR-92a mimics potentiate the activation of hepatic stellate cells (HSCs), subsequently increasing extracellular matrix (ECM) deposition in mice. Consequently, remodeling of the liver microenvironment enhanced immunosuppressive cell accumulation and cancer cell attachment. EVs miR-92a directly suppressed its target SMAD7, leading to the enhancement of transforming growth factor-β signaling in HSC. Elevated levels of circulating miR-92a are found in the sera of lung cancer patients, and EVs isolated from these patients have a similar ability to increase HSCs activation and ECM protein expression. Our study reveals the sequential steps of liver PMN formation in lung cancer, providing critical mediators that prepare PMN in the liver, and identifies new targets that offer valuable options for diagnosis and therapeutic intervention.