Glioblastoma is the most common and aggressive brain tumor and it is characterized by a high mortality rate. Temozolomide (TMZ) is an effective chemotherapy drug for glioblastoma, but the resistance to TMZ has come to represent a major clinical problem, and its underlying mechanism has yet to be elucidated. In the present study, the role of exosomal connexin 43 (Cx43) in the resistance of glioma cells to TMZ and cell migration was investigated. First, higher expression levels of Cx43 were detected in TMZ-resistant U251 (U251r) cells compared with those in TMZ-sensitive (U251s) cells. Exosomes from U251s or U251r cells (sExo and rExo, respectively) were isolated. It was found that the expression of Cx43 in rExo was notably higher compared with that in sExo, whereas treatment with rExo increased the expression of Cx43 in U251s cells. Additionally, exosomes stained with dioctadecyloxacarbocyanine (Dio) were used to visualized exosome uptake by glioma cells. It was observed that the uptake of Dio-stained rExo in U251s cells was more prominent compared with that of Dio-stained sExo, while 37,43 Gap27, a gap junction mimetic peptide directed against Cx43, alleviated the rExo uptake by cells. Moreover, rExo increased the IC 50 of U251s to TMZ, colony formation and Bcl-2 expression, but decreased Bax and cleaved caspase-3 expression in U251s cells. 37,43 Gap27 efficiently inhibited these effects of rExo on U251s cells. Finally, the results of the wound healing and Transwell assays revealed that rExo significantly enhanced the migration of U251s cells, whereas 37,43 Gap27 significantly attenuated rExo-induced cell migration. Taken together, these results indicate the crucial role of exosomal Cx43 in chemotherapy resistance and migration of glioma cells, and suggest that Cx43 may hold promise as a therapeutic target for glioblastoma in the future.
In recent years, osteosarcoma survival rates have failed to improve significantly with conventional treatment modalities because of the development of chemotherapeutic resistance. The human breast cancer resistance protein/ATP binding cassette subfamily G member 2 (BCRP/ABCG2), a member of the ATP‐binding cassette family, uses ATP hydrolysis to expel xenobiotics and chemotherapeutics from cells. CCN family member 2 (CCN2) is a secreted protein that modulates the biological function of cancer cells, enhanced ABCG2 protein expression and activation in this study via the α6β1 integrin receptor and increased osteosarcoma cell viability. CCN2 treatment downregulated miR‐519d expression, which promoted ABCG2 expression. In a mouse xenograft model, knockdown of CCN2 expression increased the therapeutic effect of doxorubicin, which was reversed by ABCG2 overexpression. Our data show that CCN2 increases ABCG2 expression and promotes drug resistance through the α6β1 integrin receptor, whereas CCN2 downregulates miR‐519d. CCN2 inhibition may represent a new therapeutic concept in osteosarcoma.
We explored how tabersonine (Tab) protected against dexamethasone (Dex)-induced osteoporosis. Osteoblasts were treated with Dex (100 µM) with or without Table (5 or 10 µM). We measured cell viability, alkaline phosphatase (ALP) activity, and mitochondrial
superoxide and reactive oxygen species levels. We used flow cytometry to explore the effects of Tab on mitochondrial membrane potential and osteoblast apoptosis. We used RT-PCR and western blotting to examine the effect of Tab on protein expression. We evaluated the effects of Tab on bone histopathology and bone mineral density in rats with Dex-induced osteoporosis. Tab increased cell viability and ALP activity, and reduced the mitochondrial superoxide, reactive oxygen species and matrix metalloproteinase levels and osteoblast apoptosis. Tab significantly reduced the levels of nuclear factor erythroid 2-related factor 2 (Nrf2), haem oxygenase-1 and NAD(P)H quinone dehydrogenase 1. Moreover, it increased the levels of mRNAs encoding runt-related transcription factor 2, bone morphogenetic protein-2 and osterix. These data suggest that Tab ameliorates Dex-induced osteoporosis by regulating the Nrf2 signalling pathway.
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