HIF1-positive and HIF1-negative glioblastoma cells compete in vitro but cooperate in tumor growth in vivo

SOX7 inhibits tumor progression of glioblastoma and is regulated by miRNA-24

Objective

Sex-determining region Y-box 7 (SOX7) is a putative tumor suppressor in various types of human cancers. In the present study, the expression and function of SOX7 was investigated in human glioblastoma (GBM) cells.

Methods

Real-time PCR and western blot were carried out to reveal the expression of SOX7 in GBM specimens and cultured cell lines. A short interfering RNA (siRNA) targeting SOX7 was synthesized and transfected into U87 cells. 3-(4,5-Dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide (MTT) assay was performed to valuate the cell proliferation ability in U87 cells. Bioinformatics analysis further predicted its regulation by microRNA-24 (miR-24). Luciferase reporter assay was performed to prove this regulation.

Results

SOX7 was downregulated in GBM specimens and cell lines. Inhibition of SOX7 in cultured U87 cells resulted in a slower growth rate. Mechanically, SOX7 was a target of miR-24, demonstrated by reporter assay.

Conclusion

SOX7 was a strong tumor suppressor regulated by miR-24 in human GBM cells.

Acceleration of bone-defect repair by using A-W MGC loaded with BMP2 and triple point-mutant HIF1α-expressing BMSCs

Background

The goal of this study is to explore the effects of A-W MGC (apatite-wollastonite magnetic bioactive glass-ceramic) loaded with BMP2 (bone morphogenetic protein 2)- and HIF1α^mu (hypoxia-inducible factor 1 mutation)-expressing BMSCs (bone marrow mesenchymal stem cells) on the bone defect repair.

Methods

(1) BMSCs were infected with viral solution containing BMP2 and HIF1α^mu with the best MOI (multiplicity of infection). The efficiency was observed via hrGFP (human renilla reniformis green fluorescent protein). (2) The cells were divided into five groups (A–E), and ALP (alkaline phosphatase) activity was measured. (3) BMP2 and HIF1α (hypoxia-inducible factor 1α) protein were measured. (4) A-W MGC was loaded with BMSCs that contain the genes and implanted into the bone defect model. The animals were sacrificed 8 and 12 weeks later. (5) The healing was measured with X-ray, histology, and biomechanics.

Results

(1) BMSCs in A–D showed high transfection efficiency. (2) ALP in A and B was higher than the others (p = 0.041 or 0.038); A was higher than B (p = 0.038); (3) BMP2 in A and B was higher than the others (p = 0.014). HIF1α in A and C was higher than the others (p = 0.020). (4) 8 and 12 weeks after, an X-ray indicated that bone defect was nearly fully repaired in A and C. (5) 12 weeks after, the bone remodeling was complete in A and C. (6) The flexural strength in A and C was stronger than the others (p = 0.043).

Conclusion

Engineered A-W MGC with BMP2 and HIF1α^mu-expressing BMSCs exhibits comparable therapeutic effects of bone-defect repair as an autologous bone graft.

Long-term exposure to hypoxia inhibits tumor progression of lung cancer in rats and mice

Background

Hypoxia has been identified as a major negative factor for tumor progression in clinical observations and in animal studies. However, the precise role of hypoxia in tumor progression has not been fully explained. In this study, we extensively investigated the effect of long-term exposure to hypoxia on tumor progression in vivo.

Methods

Rats bearing transplanted tumors consisting of A549 human lung cancer cells (lung cancer tumor) were exposed to hypoxia for different durations and different levels of oxygen. The tumor growth and metastasis were evaluated. We also treated A549 lung cancer cells (A549 cells) with chronic hypoxia and then implanted the hypoxia-pretreated cancer cells into mice. The effect of exposure to hypoxia on metastasis of Lewis lung carcinoma in mice was also investigated.

Results

We found that long-term exposure to hypoxia a) significantly inhibited lung cancer tumor growth in xenograft and orthotopic models in rats, b) significantly reduced lymphatic metastasis of the lung cancer in rats and decreased lung metastasis of Lewis lung carcinoma in mice, c) reduced lung cancer cell proliferation and cell cycle progression in vitro, d) decreased growth of the tumors from hypoxia-pretreated A549 cells, e) decreased Na⁺-K⁺ ATPase α1 expression in hypoxic lung cancer tumors, and f) increased expression of hypoxia inducible factors (HIF1α and HIF2α) but decreased microvessel density in the lung cancer tumors. In contrast to lung cancer, the growth of tumor from HCT116 human colon cancer cells (colon cancer tumor) was a) significantly enhanced in the same hypoxia conditions, accompanied by b) no significant change in expression of Na⁺-K⁺ ATPase α1, c) increased HIF1α expression (no HIF2α was detected) and d) increased microvessel density in the tumor tissues.

Conclusions

This study demonstrated that long-term exposure to hypoxia repressed tumor progression of the lung cancer from A549 cells and that decreased expression of Na⁺-K⁺ ATPase was involved in hypoxic inhibition of tumor progression. The results from this study provide new insights into the role of hypoxia in tumor progression and therapeutic strategies for cancer treatment.

Frataxin participates to the hypoxia-induced response in tumors

Defective expression of frataxin is responsible for the degenerative disease Friedreich's ataxia. Frataxin is a protein required for cell survival since complete knockout is lethal. Frataxin protects tumor cells against oxidative stress and apoptosis but also acts as a tumor suppressor. The molecular bases of this apparent paradox are missing. We therefore sought to investigate the pathways through which frataxin enhances stress resistance in tumor cells. We found that frataxin expression is upregulated in several tumor cell lines in response to hypoxic stress, a condition often associated with tumor progression. Moreover, frataxin upregulation in response to hypoxia is dependent on hypoxia-inducible factors expression and modulates the activation of the tumor-suppressor p53. Importantly, we show for the first time that frataxin is in fact increased in human tumors in vivo. These results show that frataxin participates to the hypoxia-induced stress response in tumors, thus implying that modulation of its expression could have a critical role in tumor cell survival and/or progression.

Glutaredoxin 2 prevents aggregation of mutant SOD1 in mitochondria and abolishes its toxicity

Vulnerability of motoneurons in amyotrophic lateral sclerosis (ALS) arises from a combination of several mechanisms, including protein misfolding and aggregation, mitochondrial dysfunction and oxidative damage. Protein aggregates are found in motoneurons in models for ALS linked to a mutation in the gene coding for Cu,Zn superoxide dismutase (SOD1) and in ALS patients as well. Aggregation of mutant SOD1 in the cytoplasm and/or into mitochondria has been repeatedly proposed as a main culprit for the degeneration of motoneurons. It is, however, still debated whether SOD1 aggregates represent a cause, a correlate or a consequence of processes leading to cell death. We have exploited the ability of glutaredoxins (Grxs) to reduce mixed disulfides to protein thiols either in the cytoplasm and in the IMS (Grx1) or in the mitochondrial matrix (Grx2) as a tool for restoring a correct redox environment and preventing the aggregation of mutant SOD1. Here we show that the overexpression of Grx1 increases the solubility of mutant SOD1 in the cytosol but does not inhibit mitochondrial damage and apoptosis induced by mutant SOD1 in neuronal cells (SH-SY5Y) or in immortalized motoneurons (NSC-34). Conversely, the overexpression of Grx2 increases the solubility of mutant SOD1 in mitochondria, interferes with mitochondrial fragmentation by modifying the expression pattern of proteins involved in mitochondrial dynamics, preserves mitochondrial function and strongly protects neuronal cells from apoptosis. The toxicity of mutant SOD1, therefore, mostly arises from mitochondrial dysfunction and rescue of mitochondrial damage may represent a promising therapeutic strategy.