Targeted expression of human folylpolyglutamate synthase for selective enhancement of methotrexate chemotherapy in osteosarcoma cells

CCT6A knockdown suppresses osteosarcoma cell growth and Akt pathway activation in vitro

We assessed the role of the protein-coding gene chaperonin-containing TCP1 subunit 6A (CCT6A) in osteosarcoma, as this is currently unknown. Using data from the R2 online genomic analysis and visualization application, we found that CCT6A messenger ribonucleic acid (RNA) expression is increased in osteosarcoma tissue and cells. Transfection of CCT6A small interfering RNA into cultured osteosarcoma cells revealed that CCT6A knockdown attenuates cell growth, cell viability, cell survival, and induced apoptosis and cell cycle progression at the G0/G1 phases. Moreover, CCT6A knockdown downregulated phospho-protein kinase B (p-Akt), cyclinD1 and B-cell lymphoma-2, whereas upregulated Bcl-2-associated X-protein expression. Thus, CCT6A knockdown inhibits cell proliferation, induces cell apoptosis, and suppresses the Akt pathway.

GANT61 plays antitumor effects by inducing oxidative stress through the miRNA-1286/RAB31 axis in osteosarcoma

Osteosarcoma (OS) is a rare malignancy of bone associated with poor clinical outcomes. The antitumor effects of GANT61 on OS is unclear. To investigate antitumor effects and mechanism of GANT61 in OS cells and xenograft model. Effects of GANT61 on cell viability, clone formation, cell cycle, apoptosis, migration, and invasion ability of OS cells were assessed. Reactive oxygen species (ROS) levels measured by dichlorofluorescein fluorescence were used to evaluate oxidative stress. The Xenograft model was constructed to investigate the antitumor effects of GANT61 in vivo. The microRNA (miRNA)-1286 was downregulated, while RAB31 upregulated in OS tissues and cells. GANT61 inhibited viability, migration, and invasion ability of OS cells (SaOS-2 and U2OS), and induced apoptosis and the ROS production, along with miRNA-1286 upregulation and RAB13 downregulation. After knockdown of miRNA-1286, GANT6-induced cell inhibition was attenuated, along with RAB31 upregulation. Inversely, miRNA-1286 overexpression downregulated RAB31. Dual-luciferase reporter assay verified that miR-1286 negatively targeted RAB13. Moreover, the knockdown of RAB31 stimulated apoptosis and ROS production while inhibited viability, migration, and invasion of GANT61-treated cells. In vivo experiments further confirmed that GANT61 inhibited tumor growth and RAB13 expression, but enhanced miRNA-1286. The study demonstrated that GANT61 inhibited cell aggressive phenotype and tumor growth by inducing oxidative stress through the miRNA-1286/RAB31 axis. Our findings provided a potential antitumor agent for the OS clinical treatment.

Elimination of human folypolyglutamate synthetase alters programming and plasticity of somatic cells

Folates are vital cofactors for the regeneration of S-adenosyl methionine, which is the methyl source for DNA methylation, protein methylation, and other aspects of one-carbon (C1) metabolism. Thus, folates are critical for establishing and preserving epigenetic programming. Folypolyglutamate synthetase (FPGS) is known to play a crucial role in the maintenance of intracellular folate levels. Therefore, any modulation in FPGS is expected to alter DNA methylation and numerous other metabolic pathways. To explore the role of polyglutamylation of folate, we eliminated both isoforms of FPGS in human cells (293T), producing FPGS knockout (FPGS^ko) cells. The elimination of FPGS significantly decreased cell proliferation, with a major effect on oxidative phosphorylation and a lesser effect on glycolysis. We found a substantial reduction in global DNA methylation and noteworthy changes in gene expression related to C1 metabolism, cell division, DNA methylation, pluripotency, Glu metabolism, neurogenesis, and cardiogenesis. The expression levels of NANOG, octamer-binding transcription factor 4, and sex-determining region Y-box 2 levels were increased in the mutant, consistent with the transition to a stem cell-like state. Gene expression and metabolite data also indicate a major change in Glu and GABA metabolism. In the appropriate medium, FPGS^ko cells can differentiate to produce mainly cells with characteristics of either neural stem cells or cardiomyocytes.-Srivastava, A. C., Thompson, Y. G., Singhal, J., Stellern, J., Srivastava, A., Du, J., O'Connor, T. R., Riggs, A. D. Elimination of human folypolyglutamate synthetase alters programming and plasticity of somatic cells.

Baicalin inhibits growth and induces apoptosis of human osteosarcoma cells by suppressing the AKT pathway

Osteosarcoma (OS) is one of the most prevalent types of bone malignancies with poor overall prognosis, and is reported mainly in children and adolescents. Therefore, the investigation of novel and efficient treatment strategies for patients with OS is required. Baicalin exhibits potential anticancer effects, including in OS. However, its therapeutic effect against OS and the underlying mechanisms have not been fully evaluated. In the present study, the effect of baicalin on the proliferation and apoptosis of OS cells and its underlying mechanism of AKT pathway activation was explored. Cell confluence and cell number counts revealed suppressed the growth of OS cells that were treated with baicalin. Analysis of cell viability, cell survival and cell cycle, as well as cell apoptosis revealed decreased cell viability and survival, induced cell cycle arrest and apoptosis of treated cells. Western blot analysis demonstrated significantly decreased ratios of phosphorylated-AKT/AKT and Bcl-2/Bax, and decreased protein levels of cyclin D1 and CDK4 in cells treated with baicalin. Thus, the findings from the present study suggest that the suppression of the AKT pathway may be the underlying mechanism of the antitumor effect of baicalin in OS cells.

Effect of RAB31 silencing on osteosarcoma cell proliferation and migration through the Hedgehog signaling pathway

Osteosarcoma (OS) is a prevalent cancer that plagues people worldwide. Identifying prognostic markers would be useful in treating human OS. In this study, we aimed to explore the functions of Ras-related protein Rab-31 (RAB31) in OS-cell proliferation, migration, and invasion as well as its roles in the Hedgehog signaling pathway for better understanding of the mechanism. To assess the detailed regulatory mechanism of RAB31 silencing on OS, both RT-qPCR and Western blot analysis were employed to evaluate the expressions of RAB31 as well as the Hedgehog signaling pathway-related genes. Besides, we also investigated the effects of silenced RAB31 both in vitro and in vivo. First, we found that in OS tissues, both mRNA and protein expressions of RAB31 and PCNA had a significant increase. Second, the Hedgehog signaling pathway was detected to play an integral role in OS progression. Finally, after transfection of RAB31-siRNA to reduce the expression of RAB31, the Hedgehog signaling pathway was suppressed, along with cell proliferation, invasion, and migration. Therefore, we conclude that RAB31 plays an important role in OS development and its silencing delays the OS progression via suppression of the Hedgehog signaling pathway.

SKA1 induces de novo MTX-resistance in osteosarcoma through inhibiting FPGS transcription

De novo methotrexate (MTX)-resistance, whose underlying mechanism remains largely unknown, usually leads to very poor prognosis in patients with osteosarcoma (OS). In this study, we established the de novo MTX-resistant OS cell line SF-86 and identified the candidate gene spindle and kinetochore associated complex subunit 1 (SKA1) as potentially related to de novo MTX-resistance. Analysis of a cohort of 95 OS patients demonstrated that SKA1 overexpression significantly correlated with de novo MTX-resistance and poor 5-year survival. Mechanistically, SKA1 overexpression lead to a downregulation of folylpoly-γ-glutamate synthetase (FPGS), a key enzyme that converts MTX into its active form, MTX-PG. We further demonstrated that SKA1 interacts with DNA-directed RNA polymerase II subunit RPB3. ChIP analysis revealed that RPB3 binds the promoter region of the FPGS gene and triggers FPGS transcription upon MTX treatment in SW1353, a MTX-sensitive OS cell line lacking endogenous SKA1 expression. On the contrary, this process is blocked in SF-86 cells due to the formation of an inhibitory SKA1-RPB3 complex. Furthermore, downregulation of SKA1 levels restores MTX sensitivity in SF-86. Collectively, our study has established the de novo MTX-resistant cell line SF-86 and identified SKA1 as a novel regulator of FPGS, playing a key role in the development of de novo MTX-resistance in OS.

Binding of a Smad4/Ets-1 complex to a novel intragenic regulatory element in exon12 of FPGS underlies decreased gene expression and antifolate resistance in leukemia

Polyglutamylation of antifolates catalyzed by folylpoly-γ-glutamate synthetase (FPGS) is essential for their intracellular retention and cytotoxic activity. Hence, loss of FPGS expression and/or function results in lack of antifolate polyglutamylation and drug resistance. Members of the TGF-β/Smad signaling pathway are negative regulators of hematopoiesis and deregulation of this pathway is considered a major contributor to leukemogenesis. Here we show that FPGS gene expression is inversely correlated with the binding of a Smad4/Ets-1 complex to exon12 of FPGS in both acute lymphoblastic leukemia cells and acute myeloid leukemia blast specimens. We demonstrate that antifolate resistant leukemia cells harbor a heterozygous point mutation in exon12 of FPGS which disrupts FPGS activity by abolishing ATP binding, and alters the binding pattern of transcription factors to the genomic region of exon12. This in turn results in the near complete silencing of the wild type allele leading to a 97% loss of FPGS activity. We show that exon12 is a novel intragenic transcriptional regulator, endowed with the ability to drive transcription in vitro, and is occupied by transcription factors and chromatin remodeling agents (e.g. Smad4/Ets-1, HP-1 and Brg1) in vivo. These findings bear important implications for the rational overcoming of antifolate resistance in leukemia.

Estrogen-related receptor alpha confers methotrexate resistance via attenuation of reactive oxygen species production and P53 mediated apoptosis in osteosarcoma cells

Osteosarcoma (OS) is a malignant tumor mainly occurring in children and adolescents. Methotrexate (MTX), a chemotherapy agent, is widely used in treating OS. However, treatment failures are common due to acquired chemoresistance, for which the underlying molecular mechanisms are still unclear. In this study, we report that overexpression of estrogen-related receptor alpha (ERR α ), an orphan nuclear receptor, promoted cell survival and blocked MTX-induced cell death in U2OS cells. We showed that MTX induced ROS production in MTX-sensitive U2OS cells while ERR α effectively blocked the ROS production and ROS associated cell apoptosis. Our further studies demonstrated that ERR α suppressed ROS induction of tumor suppressor P53 and its target genes NOXA and XAF1 which are mediators of P53-dependent apoptosis. In conclusion, this study demonstrated that ERR α plays an important role in the development of MTX resistance through blocking MTX-induced ROS production and attenuating the activation of p53 mediated apoptosis signaling pathway, and points to ERR α as a novel target for improving osteosarcoma therapy.