Septin 2 Research Articles

Circ_0057558 accelerates the development of prostate cancer through miR-1238-3p/SEPT2 axis.

Prostate cancer (PCa) is one of the most common malignant tumors in males with high morbidity and mortality. Existing studies have demonstrated that circ_0057558 may be a molecular marker affecting PCa. However, its detailed roles in PCa remain unclear. The levels of circ_0057558, miR-1238-3p and Septin 2 (SEPT2) were measured by quantitative real-time polymerase chain reaction (qRT-PCR). Cell counting kit-8 (CCK-8) assay, colony formation assay, 5-Ethynyl-2'-deoxyuridine (EdU) assay, flow cytometry assay, wound healing assay, transwell assay and tube formation assay were conducted for cell function identification. Xenograft tumor experiment was used to test the effect of circ_0057558 in vivo. Dual-luciferase reporter assay and RNA immunoprecipitation (RIP) assay were conducted to determine the relationships between miR-1238-3p and circ_0057558 or SEPT2. We identified that circ_0057558 level was elevated in PCa, and silencing circ_0057558 restrained PCa cell proliferation, survival, migration, invasion and angiogenesis. Circ_0057558 could sponge miR-1238-3p, and SEPT2 was the target of miR-1238-3p. Circ_0057558 promoted the expression of SEPT2 by negatively regulating miR-1238-3p, resulting in promotion of PCa progression. The effects of circ_0057558 knockdown in PCa development were overturned by the lack of miR-1238-3p. Also, overexpression of SEPT2 abolished the suppressive impacts of miR-1238-3p on PCa progression. As a tumor promoter, circ_0057558 regulated the expression of miR-1238-3p and SEPT2 and facilitated PCa progression. These results indicated that circ_0057558 was a potential therapeutic marker of PCa.

Noncanonical PDK4 action alters mitochondrial dynamics to affect the cellular respiratory status

Dynamic regulation of mitochondrial morphology provides cells with the flexibility required to adapt and respond to electron transport chain (ETC) toxins and mitochondrial DNA-linked disease mutations, yet the mechanisms underpinning the regulation of mitochondrial dynamics machinery by these stimuli is poorly understood. Here, we show that pyruvate dehydrogenase kinase 4 (PDK4) is genetically required for cells to undergo rapid mitochondrial fragmentation when challenged with ETC toxins. Moreover, PDK4 overexpression was sufficient to promote mitochondrial fission even in the absence of mitochondrial stress. Importantly, we observed that the PDK4-mediated regulation of mitochondrial fission was independent of its canonical function, i.e., inhibitory phosphorylation of the pyruvate dehydrogenase complex (PDC). Phosphoproteomic screen for PDK4 substrates, followed by nonphosphorylatable and phosphomimetic mutations of the PDK4 site revealed cytoplasmic GTPase, Septin 2 (SEPT2), as the key effector molecule that acts as a receptor for DRP1 in the outer mitochondrial membrane to promote mitochondrial fission. Conversely, inhibition of the PDK4-SEPT2 axis could restore the balance in mitochondrial dynamics and reinvigorates cellular respiration in mitochondrial fusion factor, mitofusin 2-deficient cells. Furthermore, PDK4-mediated mitochondrial reshaping limits mitochondrial bioenergetics and supports cancer cell growth. Our results identify the PDK4-SEPT2-DRP1 axis as a regulator of mitochondrial function at the interface between cellular bioenergetics and mitochondrial dynamics.

Human umbilical cord-mesenchymal stem cells-derived exosomes carrying microRNA-15a-5p possess therapeutic effects on Wilms tumor via regulating septin 2

ABSTRACT The exact mechanism of miR-15a-5p shuttled by human umbilical cord-mesenchymal stem cell-derived exosomes (hUC-MSCs-Exo) in Wilms tumor (WT) was estimated. WT tissues were collected clinically. miR-15a-5p and septin 2 (SEPT2) expression levels were examined in tissues . hUC-MSCs-Exo were transfected with miR-15a-5p-related oligonucleotides and co-cultured with WT cells (G-401). In addition, SEPT2 loss-of-function was performed in G-401 cells. The biological functions of G-401 cells after treatments were evaluated. Moreover, tumor formation tests further assessed the role of exosomal miR-15a-5p in WT. The miR-15a-5p level was lower and the SEPT2 level was higher in WT. hUC-MSCs-Exo impaired the biological functions of G-401 cells. hUC-MSCs-Exo carried upregulated miR-15a-5p into G-401 cells, thereby lessening the tumorigenic properties of G-401 cells. Inhibition of SEPT2 suppressed the biological function of WT cells and upregulated SEPT2 reversed hUC-MSCs-Exo-mediated inhibition of G-401 cell growth. The tumorigenicity of G-401 cells in mice was impaired by hUC-MSCs-Exo overexpressing miR-15a-5p. The data prove that miR-15a-5p shuttled by hUC-MSCs-Exo negatively regulates SEPT2 expression, and disrupts WT cell growth in vivo and in vitro.

The LncRNA FGD5-AS1/miR-497-5p axis regulates septin 2 (SEPT2) to accelerate cancer progression and increase cisplatin-resistance in laryngeal squamous cell carcinoma.

Aberrant expression or mutation of the Septin gene family is closely associated with cancer progression, and septin 2 (SEPT2) exerts its tumor-promoting effects in multiple cancers, but its role in regulating laryngeal squamous cell carcinoma (LSCC) progression and drug resistance has not been investigated. Based on the published data, the present study identified that SEPT2 promoted cancer progression and increased cisplatin-resistance in LSCC, and a novel LncRNA FGD5-AS1/miR-497-5p axis was crucial for this process. Mechanistically, SEPT2 tended to be enriched in LSCC tissues and cells, and knock-down of SEPT2 inhibited cell proliferation, viability, migration, and tumorigenesis in LSCC cells in vitro and in vivo. Aside from that, SEPT2 overexpression increased cisplatin resistance in LSCC cells. Next, by conducting the dual-luciferase reporter gene system assay, we identified that the LncRNA FGD5-AS1/miR-497-5p axis regulated SEPT2 in LSCC. Specifically, LncRNA FGD5-AS1 sponged miR-497-5p to upregulate SEPT2 in LSCC cells in a competing endogenous RNA (ceRNA) mechanisms-dependent manner. Interestingly, upregulated LncRNA FGD5-AS1 and downregulated miR-497-5p were observed in LSCC tissues and cells, and LncRNA FGD5-AS1 ablation inhibited cancer progression. Also, LncRNA FGD5-AS1 overexpression increased cisplatin-resistance in LSCC by modulating the miR-497-5p/SEPT2 axis. Collectively, we conclude that targeting the LncRNA FGD5-AS1/miR-497-5p/SEPT2 signaling cascade may be an alternative strategy to treat LSCC in the clinic.

MicroRNA‑744‑5p is downregulated in colorectal cancer and targets SEPT2 to suppress the malignant phenotype.

MicroRNA (miR)-744-5p serves a pivotal role in the progression of multiple cancers; however, the function of miR-744-5p in colorectal cancer (CRC) remains largely unknown. In the present study, the effects of miR-744-5p on the progression of CRC were analyzed and the mechanisms involved were investigated. It was revealed that miR-744-5p was frequently downregulated in CRC tissues and cell lines. Overexpression of miR-744-5p significantly inhibited the proliferation, colony formation, and promoted the apoptosis of CRC cells. Bioinformatics analysis revealed that Septin 2 (SEPT2) was a potential target of miR-744-5p. miR-744-5p bound the 3′-untranslated region (UTR) of SEPT2 and reduced the level of SEPT2 in CRC cells. A negative correlation between the expression of miR-744-5p and SEPT2 was observed in CRC tissues. Overexpression of SEPT2 counteracted the suppressive effect of miR-744-5p on the proliferation and apoptosis of CRC cells. Collectively, these data demonstrated the functional mechanism of miR-744-5p by targeting SEPT2, which suggested miR-744-5p as a potential target for the treatment of patients with CRC.

LncRNA AFAP1-AS1 Knockdown Represses Cell Proliferation, Migration, and Induced Apoptosis in Breast Cancer by Downregulating SEPT2 Via Sponging miR-497-5p.

Background: Long non-coding RNA actin filament-associated protein1-antisense RNA 1 (AFAP1-AS1) was confirmed to be associated with tumorigenesis. However, the role of AFAP1-AS1 in breast cancer was little known. Materials and Methods: Quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect the levels of AFAP1-AS1, microRNA-497-5p (miR-497-5p), and Septin 2 (SEPT2) in breast cancer tissues and cells. The cell proliferation, migration, and apoptosis were tested by Methylthiazolyldiphenyl-tetrazolium bromide (MTT), Transwell and Flow cytometry assays, respectively. The targeting relationship between genes was predicted by StarBase v.3.0 and confirmed by dual-luciferase reporter assay. Pearson's correlation coefficient was applied to examine the correlation between the two groups. SEPT2 protein expression was evaluated by Western blot. Xenograft models were established to investigate the role of AFAP1-AS1 knockdown in vivo. Results: AFAP1-AS1 was upregulated in breast cancer tissues and cells, and AFAP1-AS1 knockdown could hinder proliferation and migration of breast cancer cells, and contribute to cell apoptosis. MiR-497-5p, which was downregulated in breast cancer, was verified to be a target of AFAP1-AS1 and inversely correlated with AFAP1-AS1 expression. SEPT2, as a target gene of miR-497-5p, was negatively regulated by miR-497-5p and positively correlated with AFAP1-AS1 expression. Importantly, AFAP1-AS1 could upregulate SEPT2 expression by sponging miR-497-5p, and modulate cell progression by regulation of the miR-497-5p/SEPT2 axis in breast cancer. Conclusion: AFAP1-AS1 knockdown repressed the progression of breast cancer cells by sponging miR-497-5p and downregulating SEPT2.

Micropeptide MIAC Inhibits HNSCC Progression by Interacting with Aquaporin 2.

Several important micropeptides encoded by noncoding RNAs have been identified in recent years; however, there have never been any reports of micropeptides in head and neck squamous cell carcinoma (HNSCC). Here we report the discovery and characterization of a human endogenous peptide named micropeptide inhibiting actin cytoskeleton (MIAC). Comprehensive analysis of the TCGA (The Cancer Genome Atlas) database (n = 500), clinical fresh samples (n = 94), and tissue microarrays (n = 60) revealed that lower MIAC expression is correlated with poor overall survival of HNSCC patients. Meanwhile, RNA-sequencing analysis of 9657 human tissues across 32 cancer types from TCGA cohorts found that MIAC is significantly associated with the progression of 5 other different tumors. Mechanistically, MIAC directly interacts with AQP2 (Aquaporin 2) to inhibit the actin cytoskeleton by regulating SEPT2 (Septin 2)/ITGB4 (Integrin Beta 4) and ultimately suppressing the tumor growth and metastasis of HNSCC. Collectively, the mechanism investigation and evaluation of MIAC activity in vivo and in vitro highlights that MIAC plays an important role in HNSCC tumorigenesis.

Extracellular vesicle-derived circ_SLC19A1 promotes prostate cancer cell growth and invasion through the miR-497/septin 2 pathway.

The occurrence and development of prostate cancer (PCa) is complex, and the related mechanism is not fully understood. Current studies have found that extracellular vesicles (EVs) and circular RNAs (circRNAs) have important functions in various tumours and other diseases. In this study, the detection of circRNAs in PCa showed that circ_SLC19A1 was increased in PCa cells and their secreted EVs. EVs with high expression of circ_SLC19A1 could be taken up by PCa cells, which promoted cell proliferation and invasion. The sequence of circ_SLC19A1 contained multiple binding sites for miR-497, and circ_SLC19A1 could bind directly to miR-497 in cells. The expression of miR-497 was downregulated in PCa cells, while the expression of its target gene septin 2 (SEPT2) was upregulated significantly. Transfection of circ_SLC19A1 small interfering RNA (siRNA) or miR-497 mimics could significantly inhibit the expression of SEPT2 and the phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1/2). After co-transfection of circ_SLC19A1 siRNA and miR-497 inhibitors or SEPT2 overexpression vector, the expression of SEPT2 and ERK1/2 phosphorylation levels showed no significant changes. Similar results were obtained with co-transfection of miR-497 mimics and the SEPT2 overexpression vector. Therefore, cancer cells can regulate the expression of SEPT2 through miR-497 by secreting EVs with high expression of circ_SLC19A1, thus affecting the activation of the downstream ERK1/2 pathway and ultimately regulating PCa cell growth and invasion. Therefore, EV-derived circ_SLC19A1 plays an important regulatory role in PCa and may be an important target for PCa prevention and treatment.

Expression of septin 2 and association with clinicopathological parameters in colorectal cancer.

Septin 2 (SEPT2) is a tumor-related gene belonging to the SEPT family that affects the cellular processes of hepatoma carcinoma cells, glioblastoma cells and mesangial cells and is highly expressed in breast cancer, biliary tract cancer and acute myeloid leukemia. Colorectal cancer (CRC) is the third most common type of malignancy in humans. In the present study, Oncomine database was used to compare the expression pattern of SEPT2 mRNA between CRC and normal tissues. Additionally, protein expression in 90 pairs of CRC and paracancerous tissues was analyzed by western blotting and immunohistochemistry (IHC). The results showed that SEPT2 was highly expressed in CRC tissues at the mRNA and protein levels. SEPT2 expression quantified by IHC was associated with lymph node metastasis, the degree of differentiation and TNM staging. Increased SEPT2 wass associated with reduced overall survival (OS) according to Kaplan-Meier analysis. COX proportional hazard analysis indicated that SEPT2 was an independent factor that influenced the OS of patients with CRC. Therefore, SEPT2 was associated with the occurrence, progression and prognosis of CRC and thus, may be a marker and prognostic indicator of CRC.

Activation of peroxisome proliferator-activated receptor-γ (PPARγ) inhibits hepatoma cell growth via downregulation of SEPT2 expression

Hepatocellular carcinoma (HCC) is a malignant tumor with poor prognosis and low therapeutic efficacy. Recent studies have demonstrated the therapeutic prospect of peroxisome proliferator-activated receptor-γ (PPARγ) cancer angiogenesis. However, the action mechanisms remain elusive. In the present study, by using mass spectrometry, we found that PPARγ ligand rosiglitazone (RGZ) could regulate HCC cell growth by influencing various downstream factors and pathways. Among the altered proteins, septin 2 (SEPT2) was found to exhibit oncogenic function. PPARγ overexpression could inhibit the expression of SEPT2, thus blocking the promoting effects of SEPT2 on HCC cell proliferation, invasion and its inhibitory effect on cell apoptosis. Further studies also indicated that SEPT2 promoted HCC cell growth via upregulation of matrix metalloproteinase (MMP)-2 and -9, and simultaneously inhibited the cleavage of caspase-3, -7, and -9. Interestingly, the effects of SEPT2 on the above factors could be suppressed by PPARγ overexpression, suggesting that PPARγ could inhibit HCC cell growth via regulating the expression and blocking the oncogenic function of SEPT2. Taken together, these results provide new evidence for the action mechanisms of PPARγ in carcinogenesis of HCC, and upon further investigation, PPARγ could be developed as a new target for the treatment of liver cancer.

Self assembly of human septin 2 into amyloid filaments

Septins are a conserved group of GTP-binding proteins that form hetero-oligomeric complexes which assemble into filaments. These are essential for septin function, including their role in cytokinesis, cell division, exocytosis and membrane trafficking. Septin 2 (SEPT2) is a member of the septin family and has been associated with neurofibrillary tangles and other pathological features of senile plaques in Alzheimer’s disease. An in silico analysis of the amino acid sequence of SEPT2 identified regions with a significant tendency to aggregate and/or form amyloid. These were all observed within the GTP-binding domain. This was consistent with the experimental identification of a structure rich in β-sheet during temperature induced unfolding transitions observed for both the full length protein and the GTP-binding domain alone. This intermediate state is characterized by irreversible aggregation and has the ability to bind Thioflavin-T, suggesting its amyloid nature. Under electron microscopy, fibers extending for several micrometers in length could be visualized. The results shown in this study support the hypothesis that single septins, when present in excess or with unbalanced stoichiometries, may be unstable and assemble into amyloid-like structures.

A new locus in chromosome 2q37-qter is associated with posterior polar cataract

To study the genetic basis of autosomal dominant posterior polar cataracts in two Chinese pedigrees. Peripheral blood samples were collected and genomic DNA was isolated. A genome-wide scan, using microsatellite markers at approximately 10-cm intervals and additional microsatellite markers for the positive region, was performed. Haplotype data were processed using Cyrillic software (version 2.1) to define the region of the disease gene. Mutation analysis was carried out for candidate genes. Sequencing data were analyzed with the software Sequence Scanner v1.0. A maximum two-point LOD score (Z (max)) of 2.53 and 2.03 was obtained at marker D2S125 with recombination θ = 0.00 in the two families. The possible disease genes were located at approximately 8.44-cM between the marker D2S125 and the terminal of chromosome 2q, namely, 2q37-qter. Candidate genes, such as Gamma-crystallins (CRYGA-D), septin 2 (SEPT2), aquaporin 12B (AQP12B), and chemokine orphan receptor 7 (CXCR7), were sequenced but no causative mutations were found. Our results suggest that an unidentified gene in chromosome 2q37-qter is associated with posterior polar cataract, which may have an implication in understanding the genetic and molecular mechanisms of cataracts.

SEPT2 (septin 2)

Review on SEPT2 (septin 2), with data on DNA, on the protein encoded, and where the gene is implicated.

Forchlorfenuron Alters Mammalian Septin Assembly, Organization, and Dynamics

Septins are filamentous GTPases that associate with cell membranes and the cytoskeleton and play essential roles in cell division and cellular morphogenesis. Septins are implicated in many human diseases including cancer and neuropathies. Small molecules that reversibly perturb septin organization and function would be valuable tools for dissecting septin functions and could be used for therapeutic treatment of septin-related diseases. Forchlorfenuron (FCF) is a plant cytokinin previously shown to disrupt septin localization in budding yeast. However, it is unknown whether FCF directly targets septins and whether it affects septin organization and functions in mammalian cells. Here, we show that FCF alters septin assembly in vitro without affecting either actin or tubulin polymerization. In live mammalian cells, FCF dampens septin dynamics and induces the assembly of abnormally large septin structures. FCF has a low level of cytotoxicity, and these effects are reversed upon FCF washout. Significantly, FCF treatment induces mitotic and cell migration defects that phenocopy the effects of septin depletion by small interfering RNA. We conclude that FCF is a promising tool to study mammalian septin organization and functions.

Epithelial polarity requires septin coupling of vesicle transport to polyglutamylated microtubules

In epithelial cells, polarized growth and maintenance of apical and basolateral plasma membrane domains depend on protein sorting from the trans-Golgi network (TGN) and vesicle delivery to the plasma membrane. Septins are filamentous GTPases required for polarized membrane growth in budding yeast, but whether they function in epithelial polarity is unknown. Here, we show that in epithelial cells septin 2 (SEPT2) fibers colocalize with a subset of microtubule tracks composed of polyglutamylated (polyGlu) tubulin, and that vesicles containing apical or basolateral proteins exit the TGN along these SEPT2/polyGlu microtubule tracks. Tubulin-associated SEPT2 facilitates vesicle transport by maintaining polyGlu microtubule tracks and impeding tubulin binding of microtubule-associated protein 4 (MAP4). Significantly, this regulatory step is required for polarized, columnar-shaped epithelia biogenesis; upon SEPT2 depletion, cells become short and fibroblast-shaped due to intracellular accumulation of apical and basolateral membrane proteins, and loss of vertically oriented polyGlu microtubules. We suggest that septin coupling of the microtubule cytoskeleton to post-Golgi vesicle transport is required for the morphogenesis of polarized epithelia.

Mammalian SEPT2 Is Required for Scaffolding Nonmuscle Myosin II and Its Kinases

Mammalian septin SEPT2 belongs to a conserved family of filamentous GTPases that are associated with actin stress fibers in interphase cells and the contractile ring in dividing cells. Although SEPT2 is essential for cytokinesis, its role in this process remains undefined. Here, we report that SEPT2 directly binds nonmuscle myosin II (myosin II), and this association is important for fully activating myosin II in interphase and dividing cells. Inhibition of the SEPT2-myosin II interaction in interphase cells results in loss of stress fibers, while in dividing cells this causes instability of the ingressed cleavage furrow and dissociation of the myosin II from the Rho-activated myosin kinases ROCK and citron kinase. We propose that SEPT2-containing filaments provide a molecular platform for myosin II and its kinases to ensure the full activation of myosin II that is necessary for the final stages of cytokinesis.