Knockdown of growth-arrest-specific gene 7b (gas7b) using short-hairpin RNA desensitizes neuroblastoma cells to cisplatin: Implications for preventing apoptosis of neurons

Gas7 attenuates hepatocellular carcinoma progression and chemoresistance through the PI3K/Akt signaling pathway

Growth arrest-specific gene 7 (Gas7) was involved in various cellular functions, although its specific roles and molecular mechanisms in hepatocellular carcinoma (HCC) remained unclear. So the current study was to investigate the role of Gas7 in HCC. Our findings revealed that Gas7 was downregulated in various HCC cell lines and low Gas7 expression was associated with decreased overall survival in patients with HCC. Additionally, our functional assays showed that Gas7 inhibited cell proliferation and migration, induced cell cycle arrest, apoptosis, and autophagy, and enhanced oxaliplatin sensitivity by inhibiting the PI3K/Akt signaling pathway. We also observed that transcription factorSp1 was responsible for inhibiting Gas7. These findings provide insights into the role and elucidated a potential mechanism of Gas7 in HCC progression and metastasis. It was also observed that the Sp1/Gas7/PI3K/Akt axis was critical for malignant phenotype and oxaliplatin sensitivity in HCC. Therefore, Gas7 can be considered as a prognostic predictor and therapeutic target for HCC.

Association of germline variation with the survival of women with BRCA1/2 pathogenic variants and breast cancer

Germline genetic variation has been suggested to influence the survival of breast cancer patients independently of tumor pathology. We have studied survival associations of genetic variants in two etiologically unique groups of breast cancer patients, the carriers of germline pathogenic variants in BRCA1 or BRCA2 genes. We found that rs57025206 was significantly associated with the overall survival, predicting higher mortality of BRCA1 carrier patients with estrogen receptor-negative breast cancer, with a hazard ratio 4.37 (95% confidence interval 3.03-6.30, P = 3.1 × 10-9). Multivariable analysis adjusted for tumor characteristics suggested that rs57025206 was an independent survival marker. In addition, our exploratory analyses suggest that the associations between genetic variants and breast cancer patient survival may depend on tumor biological subgroup and clinical patient characteristics.

Solution NMR structure and ligand identification of human Gas7 SH3 domain reveal a typical SH3 fold but a non-canonical ligand-binding mode

Growth arrest specific 7 (Gas7) protein is a cytoskeleton regulator playing a crucial role in neural cell development and function, and has been implicated in Alzheimer disease, schizophrenia and cancers. In human, three Gas7 isoforms can be expressed from a single Gas7 gene, while only the longest isoform, hGas7c, possesses an SH3 domain at the N-terminus. To date, the structure and function of hGas7 SH3 domain are still unclear. Here, we reported the solution NMR structure of hGas7 SH3 domain (hGas7-SH3), which displays a typical SH3 β-barrel fold comprising five β-strands and one 3₁₀-helix. Structural and sequence comparison showed that hGas7-SH3 shares high similarity with Abl SH3 domain, which binds to a high-affinity proline-rich peptide P41 in a canonical SH3-ligand binding mode through two hydrophobic pockets and a specificity site in the RT-loop. However, unlike Abl-SH3, only six residues in the RT-loop and two residues adjacent to but not in the two hydrophobic pockets of hGas7-SH3 showed significant chemical shift perturbations in NMR titrations, suggesting a low affinity and a non-canonical binding mode of hGas7-SH3 for P41. Furthermore, four peptides selected from phage-displayed libraries also bound weakly to hGas7-SH3, and the binding region of hGas7-SH3 was mainly located in the RT-loop as well. The ligand identifications through structural similarity searching and peptide library screening in this study imply that although hGas7-SH3 adopts a typical SH3 fold, it probably possesses distinctive ligand-binding specificity.

Role of miRNA in the regulation of cannabidiol-mediated apoptosis in neuroblastoma cells

Neuroblastoma (NBL) is one of the most common childhood cancers that originate from the immature nerve cells of the sympathetic system. Studies with NBL cancers have also shown that miRNAs are dysregulated and may play a critical role in pathogenesis. Cannabidiol (CBD) is a non-psychoactive compound found in marijuana which has been previously shown by our laboratory and others to induce apoptosis in cancer cells. However, there are no studies reported to test if CBD mediates these effects through regulation of miRNA. In the current study, therefore, we investigated if CBD induces apoptosis in human NBL cell lines, SH SY5Y and IMR-32, and if it is regulated by miRNA. Our data demonstrated that CBD induces apoptosis in NBL cells through activation of serotonin and vanilloid receptors. We also found that caspase-2 and -3 played an important role in the induction of apoptosis. CBD also significantly reduced NBL cell migration and invasion in vitro. Furthermore, CBD blocked mitochondrial respiration and caused a shift in metabolism towards glycolysis. CBD altered the expression of miRNA specifically, down-regulating hsa-let-7a and upregulating hsa-mir-1972. Downregulation of let-7a increased expression of target caspase-3, and growth arrest specific-7 (GAS-7) genes. Upregulation of hsa-mir-1972 caused decreased expression of BCL2L1 and SIRT2 genes. Together, our studies suggest that CBD-mediated apoptosis in NBL cells is regulated by miRNA.

Growth arrest-specific protein 7 regulates the murine M1 alveolar macrophage polarization

Growth arrest-specific gene 7 (Gas7) is preferentially expressed in terminally differentiated brain cells and plays a crucial role during neuronal development and neurite outgrowth. Apart from that, Gas7 was found to be abundantly expressed in immune cells like murine macrophage without knowing the actual roles in immune reaction. By using the Illumina microarray analysis, we observed a clear induction of Gas7 but no other Gas family members in murine M1-polarized alveolar macrophage, which was further confirmed by RT-qPCR, Western blotting, and immunostaining analysis, suggesting a likelihood that Gas7 may participate in murine alveolar macrophage polarization. Moreover, we found that the upregulation of Gas7 in M1-polarized alveolar macrophage was almost fully blocked by IKK selective inhibitor BMS, which links Gas7 induction to nuclear factor kappa beta (NF-κB) signaling activation. Interestingly, we found that Gas7 knockdown by small interfering RNA transfection did not affect the pro-inflammatory cytokine gene Tnf and Ilb expression, whereas the expressions of canonic M1 marker gene Nos2 and other M1-dependent genes Il12b, Il6, Cxcl1, Cxcl2, and Cxcl9 were found to be reduced. Furthermore, Gas7-related M1 gene expression in alveolar macrophage was not dependent on NF-κB and STAT1 pathway. Our results demonstrate that Gas7 is potentially involved in regulation of murine M1 alveolar macrophage polarization.

HIGHLIGHTS

Gas7 was induced in LPS/IFNγ mediated M1 polarization. Gas7 are induced during time course of M1 polarization. Gas7 upregulation was dependent on NF-κB pathway in M1 polarized AMs. Gas7 knockdown reduced the M1 markers gene expression in M1 polarized AMs.

Cadmium-Associated Differential Methylation throughout the Placental Genome: Epigenome-Wide Association Study of Two U.S. Birth Cohorts

BACKGROUND

Cadmium (Cd) is a ubiquitous environmental toxicant that can accumulate in the placenta during pregnancy, where it may impair placental function and affect fetal development.

OBJECTIVES

We aimed to investigate Cd-associated variations in placental DNA methylation (DNAM) and associations with gene expression; we also aimed to identify novel pathways involved in Cd-associated reproductive toxicity.

METHODS

Using placental DNAM and Cd concentrations in the New Hampshire Birth Cohort Study (NHBCS, n=343) and the Rhode Island Child Health Study (RICHS, n=141), we performed an epigenome-wide association study (EWAS) between Cd and DNAM, adjusting for tissue heterogeneity using a reference-free method. Cohort-specific results were aggregated via inverse variance weighted fixed effects meta-analysis, and variably methylated CpGs were associated with gene expression. We then performed functional enrichment analysis and tests for associations between gene expression and birth size metrics.

RESULTS

We identified 17 Cd-associated differentially methylated CpG sites with meta-analysis p-values<1×10⁻⁵, two of which were within a 5% false discovery rate (FDR). DNAM levels at 9 of the 17 loci were associated with increased expression of 6 genes (5% FDR): TNFAIP2, EXOC3L4, GAS7, SREBF1, ACOT7, and RORA. Higher placental expression of TNFAIP2 and ACOT7 and lower expression of RORA were associated with lower birth weight z-scores (p-values<0.05).

CONCLUSION

Cd-associated differential DNAM and corresponding DNAM-expression associations were observed at loci involved in inflammatory signaling and cell growth. The expression levels of genes involved in inflammatory signaling (TNFAIP2, ACOT7, and RORA) were also associated with birth weight, suggesting a role for inflammatory processes in Cd-associated reproductive toxicity. https://doi.org/10.1289/EHP2192.

MiR-181a contributes gefitinib resistance in non-small cell lung cancer cells by targeting GAS7

Tyrosine kinase inhibitors (TKIs) exert potent therapeutic efficacy in non-small cell lung cancers (NSCLC) harboring epidermal growth factor receptor (EGFR) activating mutations. However, a major impediment for the effective treatment is the development of drug resistance. Some evidence supports a role for miRNAs in modulating NSCLC TKIs resistance. Here we show that miR-181a is significantly up-regulated in gefitinib-resistant cells compared with gefitinib-sensitive cells. Upregulation of miR-181a caused resistance of gefitinib, whereas downregulation of miR-181a sensitized NSCLC cells to gefitinib. Furthermore, the miR-181a plasma levels were significantly increased in acquired gefitinib resistant NSCLC patients compared with the plasma levels prior to gefitinib treatment in each patient. Bioinformatics analysis and luciferase reporter assay showed that growth arrest-specific 7 (GAS7) was a direct target gene of miR-181a. A significant inverse correlation between the expression of miR-181a and GAS7 was identified in NSCLC tissues. Downregulation of GAS7 expression could antagonize gefitinib re-sensitivity in PC9GR mediated by knockdown of miR-181a via AKT/ERK pathways and epithelial-to-mesenchymal transition markers. Additionally, GAS7 expression was downregulated in a large cohort of NSCLC patients, and a high mRNA level of GAS7 was associated with improved overall survival. Collectively, our findings provide a novel basis for using miR-181a/GAS7-based therapeutic strategies to reverse gefitinib resistance in NSCLC.

Oxaliplatin inhibits proliferation and migration of human hepatocellular carcinoma cells via GAS7C and the N-WASP/FAK/F-actin pathway

The growth arrest-specific gene 7 (GAS7), a member of the growth-arrest-specific family, encodes three protein isoforms (GAS7A, GAS7B, and GAS7C) and plays a potential role in lung cancer as a tumor suppressor gene. In the present study, we found low endogenous expressions of GAS7C mRNA and protein in hepatocellular carcinoma (HCC) cell lines compared with normal liver cells, and that there was a distinct increase of GAS7C expression in HCC cells treated with oxaliplatin. CCK8, apoptosis, and Transwell migration assays showed that cell proliferation and motility of HepG2 and MHCC-97 H cells were inhibited by oxaliplatin, while apoptosis was increased. Interestingly, western blot analysis showed that treatment with oxaliplatin increased GAS7C and N-WASP protein levels and decreased the levels of proteins involved in the fibronectin/integrin/FAK pathway, such as FAK, in both HCC cell lines. In addition, ectopically overexpressed GAS7C obviously inhibited cell proliferation and cell motility. Flow cytometry results showed that overexpression of GAS7C induced apoptosis of HepG2 and MHCC-97 H cells. We further confirmed the correlation between GAS7C and the N-WASP/FAK/F-actin pathway by q-PCR and western blot analysis of in GAS7C-overexpressing HepG2 and MHCC-97 H cells. Inhibition of GAS7C substantially reversed the anti-cancer effect of oxaliplatin and blocked the activity of the N-WASP/FAK/F-actin pathway. Taken together, our results showed that oxaliplatin inhibits HCC cell proliferation and migration ability by up-regulating GAS7C and activating the N-WASP/FAK/F-actin pathway.

Growth-arrest-specific 7C protein inhibits tumor metastasis via the N-WASP/FAK/F-actin and hnRNP U/β-TrCP/β-catenin pathways in lung cancer

Growth-arrest-specific 7 (GAS7) belongs to a group of adaptor proteins that coordinate the actin cytoskeleton. Among human GAS7 isoforms, only GAS7C possesses a Src homology 3 domain. We report here that GAS7C acts as a migration suppressor and can serve as a prognostic biomarker in lung cancer. GAS7C overexpression reduces lung cancer migration, whereas GAS7C knockdown enhances cancer cell migration. Importantly, ectopically overexpressed GAS7C binds tightly with N-WASP thus inactivates the fibronectin/integrin/FAK pathway, which in turn leads to the suppression of F-actin dynamics. In addition, overexpression of GAS7C sequesters hnRNP U and thus decreases the level of β-catenin protein via the β-TrCP ubiquitin-degradation pathway. The anti-metastatic effect of GAS7C overexpression was also confirmed using lung cancer xenografts. Our clinical data indicated that 23.6% (25/106) of lung cancer patients showed low expression of GAS7C mRNA which correlated with a poorer overall survival. In addition, low GAS7C mRNA expression was detected in 60.0% of metastatic lung cancer patients, indicating an association between low GAS7C expression and cancer progression. A significant inverse correlation between mRNA expression and promoter hypermethylation was also found, which suggests that the low level of GAS7C expression was partly due to promoter hypermethylation. Our results provide novel evidence that low GAS7C correlates with poor prognosis and promotes metastasis in lung cancer. Low GAS7C increases cancer cell motility by promoting N-WASP/FAK/F-actin cytoskeleton dynamics. It also enhances β-catenin stability via hnRNP U/β-TrCP complex formation. Therefore, GAS7C acts as a metastasis suppressor in lung cancer.

Low Doses of Cisplatin Induce Gene Alterations, Cell Cycle Arrest, and Apoptosis in Human Promyelocytic Leukemia Cells

Cisplatin is a known antitumor drug, but its mechanisms of action are not fully elucidated. In this research, we studied the anticancer potential of cisplatin at doses of 1, 2, or 3 µM using HL-60 cells as a test model. We investigated cisplatin effects at the molecular level using RNA sequencing, cell cycle analysis, and apoptotic assay after 24, 48, 72, and 96 hours of treatment. The results show that many genes responsible for molecular and cellular functions were significantly altered. Cisplatin treatment also caused the cells to be arrested at the DNA synthesis phase, and as the time increases, the cells gradually accumulated at the sub-G1 phase. Also, as the dose increases, a significant number of cells entered into the apoptotic and necrotic stages. Altogether, the data show that low doses of cisplatin significantly impact the viability of HL-60 cells, through modulation of gene expression, cell cycle, and apoptosis.

Growth-Arrest-Specific 7 Gene Regulates Neural Crest Formation and Craniofacial Development in Zebrafish

Growth-arrest-specific 7 (Gas7) is preferentially expressed in the nervous system and plays an important role during neuritogenesis in vertebrates. We recently demonstrated that gas7 is highly expressed in zebrafish neurons, where it regulates neural development. The possibility that gas7 may also regulate the development of other tissues remains to be examined. In this study, we investigate the role of Gas7 in the development of craniofacial tissues. Knockdown of gas7 using morpholino oligomers produced abnormal phenotypes in neural crest (NC) cells and their derivatives. NC-derived cartilage maturation was altered in Gas7 morphants as revealed by aberrant sox9b and dlx2 expression, a phenotype that could be rescued by coinjection of gas7 mRNA. While rhombomere morphology remained normal in Gas7 morphants, we observed reduced expression of the prechondrogenic genes sox9b and dlx2 in cells populating the posterior pharyngeal arches, but the fundamental structure of pharyngeal arches was preserved. In addition, NC cell sublineages that migrate to form neurons, glial cells, and melanocytes were altered in Gas7 morphants as revealed by aberrant expression of neurod, foxd3, and mitfa, respectively. Development of NC progenitors was also examined in Gas7 morphants at 12 hpf, and we observed that the reduction of cell precursors in Gas7 morphants was due to increased apoptosis level. These results indicate that the formation of NC progenitors and derivatives depends on Gas7 expression. Our observations also suggest that Gas7 regulates the formation of NC derivatives constituting the internal tissues of pharyngeal arches, without affecting the fundamental structure of mesodermal-derived pharyngeal arches.

Gas7 is required for mesenchymal stem cell-derived bone development

Mesenchymal stem cells (MSCs) can differentiate into osteoblasts and lead to bone formation in the body. Osteoblast differentiation and bone development are regulated by a network of molecular signals and transcription factors induced by several proteins, including BMP2, osterix, and Runx2. We recently observed that the growth-arrest-specific 7 gene (Gas7) is upregulated during differentiation of human MSCs into osteoblasts. Downregulation of Gas7 using short-hairpin RNA decreased the expression of Runx2, a master regulator of osteogenesis, and its target genes (alkaline phosphatase, type I collagen, osteocalcin, and osteopontin). In addition, knockdown of Gas7 decreased the mineralization of dexamethasone-treated MSCs in culture. Conversely, ectopic expression of Gas7 induced Runx2-dependent transcriptional activity and gene expression leading to osteoblast differentiation and matrix mineralization. Genetic mutations of the Gas7 gene increased body fat levels and decreased bone density in mice. These results showed that Gas7 plays a role in regulating the pathways which are essential for osteoblast differentiation and bone development. In this review, we summarize the involvement of Gas7 in MSC-based osteogenesis and osteoporosis and describe the possible mechanisms responsible for the maintenance of cellular homeostasis in MSCs and osteoblasts.

Identification and functional characterization of zebrafish Gas7 gene in early development

Growth arrest-specific 7 (Gas7) is preferentially expressed in the nervous system and plays an important role during neuritogenesis in mammals. However, the structure and function of Gas7 homologs have not been studied in nonmammalian vertebrates used as models. In this report, we identify a Gas7 gene in zebrafish that we termed zfGas7. The transcript of this gene was produced by canonical splicing, and its protein product contained a Fes/CIP4 homology and a coiled-coil domain. In early zebrafish embryos, RT-PCR analyses revealed that zfGas7 was initially expressed at 5.3 hr postfertilization (hpf), followed by an increase of expression at 10 hpf and further accumulation during somitogenesis at 48 hpf. Spatiotemporal analyses further showed that Gas7 mRNA was detected in the brain, somite, and posterior presomitic mesoderm regions during somitogenesis. At 36 hpf, zfGas7 mRNA was detected in the brain and somite but was later found only in neuronal clusters of the brain at 52 hpf. Gas7 knockdown with morpholino antisense oligonucleotides (Gas7MO) reduced the number of HuC-positive neurons in the trigeminal and statoacoustic ganglions and produced deformed phenotypes, such as flattening of the top of the head. Notably, the neuron reduction and deformed phenotypes observed in Gas7MO embryos were partially rescued by ectopic expression of Gas7. Because altered somitogenesis and pigmentation were also found in the morphants, the neuronal phenotypes observed likely are due to a general developmental delay of embryogenesis. These results indicate that Gas7 is expressed in neuronal cells but is not specifically required for neuronal development in vertebrates.

Alzheimer's disease-related protein hGas7b interferes with kinesin motility

In the previous study, we reported the important properties of hGas7b (i) that binds to phospho-tau and facilitates microtubule polymerization and (ii) the level of hGas7b is very low in the brains of patients with Alzheimer's disease. These results led us to study the function of hGas7b in detail. We focused on the effect of hGas7b on microtubule dynamics in the absence of tau, on the assumption of healthy tau decrease in the brains of Alzheimer's disease. hGas7b binds to microtubule directly without tau, although this binding does not enhance microtubule polymerization. Excess hGas7b interferes with kinesin motility on microtubules. These results suggest that regulation to maintain an appropriate concentration of hGas7b is required for healthy neurotransmission.

Gas7 mediates the differentiation of human bone marrow-derived mesenchymal stem cells into functional osteoblasts by enhancing Runx2-dependent gene expression

The differentiation of bone marrow mesenchymal stem cells (MSCs) into osteoblasts is a crucial step during bone formation. However, the mechanisms regulating the early stages of osteogenic differentiation are not fully understood. In the present study, we found that growth-arrest specific gene 7b (Gas7b) was up-regulated during dexamethasone-induced differentiation of human MSCs (hMSCs) into osteoblasts. Knockdown of Gas7 using short-hairpin RNA decreased the expression of the osteogenic transcription factor Runx2 and its target genes alkaline phosphatase, type I collagen, osteocalcin (OC), and osteopontin. In addition, knockdown of Gas7 decreased matrix mineralization of dexamethasone-treated hMSCs in vitro. In contrast, ectopic expression of Gas7 isoforms a and b promoted gene expression associated with osteoblast differentiation and matrix mineralization, and also induced the mineralization of hMSCs in vitro. Furthermore, a gene reporter assay designed to monitor OC expression in hMSCs revealed that Runx2-dependent transcriptional activity was enhanced by over-expression of human Gas7 isoforms a and b. These findings reveal that Gas7 regulates the differentiation of hMSCs into osteoblasts by enhancing Runx2-dependent gene expression.