IL-17A inhibits the degradation of RANKL in osteoblasts by inhibiting BCL2-Beclin1-autophagy signaling.

The inflammatory cytokine IL-17A is known to have the capacity to promote osteoclastogenesis, thereby enhancing bone loss. Moreover, IL-17A can promote the expression of RANKL in osteoblasts, contributing to its pro-osteoclastogenic effect. IL-17A is an autophagy regulator, which is also responsible for its regulation on RANKL expression. However, the specific role of autophagy in IL-17A-regulated RANKL expression and the underlying mechanism of IL-17A-regulated osteoblast autophagy remain unclear. IL-17A is known to inhibit autophagy by preventing BCL2 degradation. This study aimed to explore the significance of BCL2-dependent autophagy in IL-17A-regulated RANKL expression. Our results showed that IL-17A at 50 ng/mL could inhibit autophagic activity and promote RANKL protein expression in MC3T3-E1 osteoblast line. Moreover, the corresponding concentration of IL-17A could enhance BCL2 protein expression and the protein interaction between BCL2 and Beclin1 in MC3T3-E1 cells. However, the protein expression of RANKL and BCL2 promoted by 50 ng/mL of IL-17A was blocked by autophagy activation with Beclin1 pharmacological upregulation. Furthermore, RANKL protein expression promoted by 50 ng/mL of IL-17A was also reversed by autophagy activation with BCL2 knockdown. Importantly, the supernatant from osteoblasts treated with 50 ng/mL of IL-17A made osteoclast precursors (OCPs) form larger osteoclasts, which was reversed by BCL2 knockdown in osteoblasts. In conclusion, high levels of IL-17A prevent the degradation of RANKL by inhibiting BCL2-Beclin1-autophagy activation signal transduction in osteoblasts, thereby indirectly promoting osteoclastogenesis.

Identification of Gαi3 as a promising target for osteosarcoma treatment.

Sustained activation of multiple receptor tyrosine kinases (RTKs) simultaneously is vital for tumorigenesis and progression of osteosarcoma (OS). Gαi proteins recruitment to various RTKs mediates downstream oncogenic signaling activation. The expression, functions and underlying mechanisms of Gαi3 in human OS were examined. Expression of Gαi3 is robustly elevated in human OS tissues and is correlated with a poor overall survival. In patient-derived primary OS cells and immortalized lines (MG63 and U2OS), Gαi3 depletion, by shRNA and CRISPR/Cas9 strategies, robustly suppressed cell viability, proliferation and migration, while provoking G1-S arrest and apoptosis activation. Conversely, Gαi3 overexpressing ectopically can accelerate proliferation and migration of OS cells. In OS cells, Gαi3 immunoprecipitated with VEGFR2, FGFR, PGDFR and EGFR, mediating downstream cascade transduction. Akt-mTOR activation in primary OS cells was potently inhibited by Gαi3 shRNA, knockout or dominant negative mutation, but augmented after Gαi3 overexpression. In vivo studies showed that Gαi3 shRNA AAV (adeno-associated viruses) intratumoral injection largely inhibited the growth of subcutaneous xenografts of primary OS cells. Moreover, the growth of the Gαi3-knockout primary OS xenografts was much slower than that of OS xenografts with empty vector. In Gαi3-depleted OS xenografts tissues, Gαi3 downregulation and Akt-mTOR inactivation were detected. Taken together, overexpressed Gαi3 mediates RTK-Akt signaling to drive OS progression.

Identification of mitochondrial RNA polymerase as a potential therapeutic target of osteosarcoma.

POLRMT (RNA polymerase mitochondrial) is essential for transcription of mitochondrial genome encoding components of oxidative phosphorylation process. The current study tested POLRMT expression and its potential function in osteosarcoma (OS). The Cancer Genome Atlas (TCGA) cohorts and Gene Expression Profiling Interactive Analysis (GEPIA) database both show that POLRMT transcripts are elevated in OS tissues. In addition, POLRMT mRNA and protein levels were upregulated in local OS tissues as well as in established and primary human OS cells. In different OS cells, shRNA-induced stable knockdown of POLRMT decreased cell viability, proliferation, migration, and invasion, whiling inducing apoptosis activation. CRISPR/Cas9-induced POLRMT knockout induced potent anti-OS cell activity as well. Conversely, in primary OS cells ectopic POLRMT overexpression accelerated cell proliferation and migration. In vivo, intratumoral injection of adeno-associated virus-packed POLRMT shRNA potently inhibited U2OS xenograft growth in nude mice. Importantly, levels of mitochondrial DNA, mitochondrial transcripts and expression of respiratory chain complex subunits were significantly decreased in U2OS xenografts with POLRMT shRNA virus injection. Together, POLRMT is overexpressed in human OS, promoting cell growth in vitro and in vivo. POLRMT could be a novel therapeutic target for OS.

PF-06409577 Activates AMPK Signaling and Inhibits Osteosarcoma Cell Growth.

Osteosarcoma (OS) is a common primary bone malignancy. We here investigated the potential activity of PF-06409577, a novel, potent, and direct activator of AMP-activated protein kinase (AMPK), against human OS cells. In established (U2OS, MG-63, and SaOs-2 lines) and primary human OS cells, PF-06409577 inhibited cell viability and proliferation, while inducing cell apoptosis and cell cycle arrest. PF-06409577 induced AMPK activation, mTORC1 inhibition, autophagy induction, and downregulation of multiple receptor tyrosine kinase inOS cells. AMPK inactivation by AMPKα1 shRNA, CRISPR/Cas9 knockout, or dominant negative mutation (T172A) was able to abolish PF-06409577-induced activity in OS cells. In vivo, PF-06409577 oral administration at well-tolerated doses potently inhibited growth of U2OS cells and primary human OS cells in severe combined immunodeficient mice. AMPK activation, mTORC1 inhibition, autophagy induction, as well as RTK degradation and apoptosis activation were detected in PF-06409577-treated xenografts. In conclusion, activation of AMPK by PF-06409577 inhibits OS cell growth.

The histone acetyltransferase HBO1 functions as a novel oncogenic gene in osteosarcoma.

HBO1 (KAT7 or MYST2) is a histone acetyltransferase that acetylates H3 and H4 histones. Methods: HBO1 expression was tested in human OS tissues and cells. Genetic strategies, including shRNA, CRISPR/Cas9 and overexpression constructs, were applied to exogenously alter HBO1 expression in OS cells. The HBO1 inhibitor WM-3835 was utilized to block HBO1 activation. Results:HBO1 mRNA and protein expression is significantly elevated in OS tissues and cells. In established (MG63/U2OS lines) and primary human OS cells, shRNA-mediated HBO1 silencing and CRISPR/Cas9-induced HBO1 knockout were able to potently inhibit cell viability, growth, proliferation, as well as cell migration and invasion. Significant increase of apoptosis was detected in HBO1-silenced/knockout OS cells. Conversely, ectopic HBO1 overexpression promoted OS cell proliferation and migration. We identified ZNF384 (zinc finger protein 384) as a potential transcription factor of HBO1. Increased binding between ZNF384 and HBO1 promoter was detected in OS cell and tissues, whereas ZNF384 silencing via shRNA downregulated HBO1 and produced significant anti-OS cell activity. In vivo, intratumoral injection of HBO1 shRNA lentivirus silenced HBO1 and inhibited OS xenograft growth in mice. Furthermore, growth of HBO1-knockout OS xenografts was significantly slower than the control xenografts. WM-3835, a novel and high-specific small molecule HBO1 inhibitor, was able to potently suppressed OS cell proliferation and migration, and led to apoptosis activation. Furthermore, intraperitoneal injection of a single dose of WM-3835 potently inhibited OS xenograft growth in SCID mice. Conclusion: HBO1 overexpression promotes OS cell growth in vitro and in vivo.

The therapeutic value of the SphK1-targeting microRNA-3677 in human osteosarcoma cells.

Sphingosine kinase 1 (SphK1) is a potential therapeutic target for human osteosarcoma (OS). SphK1-targeting microRNAs (miRNAs) could have important therapeutic value for OS. We discovered that micorRNA-3677 (miR-3677) is a SphK1-targeting miRNA, inhibiting OS cell progression. The results of RNA-Pull down assay confirmed direct binding between biotinylated-miR-3677 and SphK1 mRNA in primary human OS cells. In established and primary human OS cells forced overexpression of miR-3677, by a lentiviral construct, decreased SphK1 3'-UTR (untranslated region) activity and downregulated SphK1 expression. Both were however enhanced with miR-3677 inhibition in OS cells. Function studies demonstrated that OS cell growth, proliferation and migration were inhibited with miR-3677 overexpression, but augmented with miR-3677 inhibition. MiR-3677 overexpression-induced anti-OS cell activity was reversed with re-expression of the 3'-UTR-depleted SphK1. Additionally, in SphK1 knockout OS cells (by CRISPR/Cas9 strategy), altering miR-3677 expression failed to further alter cell functions. Finally, we show that miR-3677 expression was significantly downregulated in primary human OS tissues, correlating with SphK1 mRNA upregulation. We conclude that targeting SphK1 by miR-3677 inhibits human OS cell progression.

microRNA-135b expression silences Ppm1e to provoke AMPK activation and inhibit osteoblastoma cell proliferation.

Forced-activation of AMP-activated protein kinase (AMPK) can possibly inhibit osteoblastoma cells. Here, we aim to provoke AMPK activation via microRNA silencing its phosphatase Ppm1e (protein phosphatase Mg2+/Mn2+-dependent 1e). We showed that microRNA-135b-5p ("miR-135b-5p"), the anti-Ppm1e microRNA, was significantly downregulated in human osteoblastoma tissues. It was correlated with Ppm1e upregulation and AMPKα1 de-phosphorylation. Forced-expression of miR-135b-5p in human osteoblastoma cells (MG-63 and U2OS lines) silenced Ppm1e, and induced a profound AMPKα1 phosphorylation (at Thr-172). Osteoblastoma cell proliferation was inhibited after miR-135b-5p expression. Intriguingly, Ppm1e shRNA knockdown similarly induced AMPKα1 phosphorylation, causing osteoblastoma cell proliferation. Reversely, AMPKα1 shRNA knockdown or dominant negative mutation almost abolished miR-135b-5p's actions in osteoblastoma cells. Further in vivo studies demonstrated that U2OS tumor growth in mice was dramatically inhibited after expressing miR-135b-5p or Ppm1e shRNA. Together, our results suggest that miR-135b-induced Ppm1e silence induces AMPK activation to inhibit osteoblastoma cell proliferation.

Identification of DNA-PKcs as a primary resistance factor of salinomycin in osteosarcoma cells.

Malignant osteosarcoma (OS) is still a deadly disease for many affected patients. The search for the novel anti-OS agent is extremely urgent and important. Our previous study has proposed that salinomycin is a novel anti-OS agent. Here we characterized DNA-dependent protein kinase catalytic subunit (DNA-PKcs) as a primary salinomycin resistance factor in OS cells. DNA-PKcs inhibitors (NU7026, NU7441 and LY294002) or DNA-PKcs shRNA knockdown dramatically potentiated salinomycin-induced death and apoptosis of OS cells (U2OS and MG-63 lines). Further, forced-expression of microRNA-101 ("miR-101") downregulated DNA-PKcs and augmented salinomycin's cytotoxicity against OS cells. Reversely, over-expression of DNA-PKcs in OS cells inhibited salinomycin's lethality. For the mechanism study, we show that DNA-PKcs is required for salinomycin-induced pro-survival autophagy activation. DNA-PKcs inhibition (by NU7441), shRNA knockdown or miR-101 expression inhibited salinomycin-induced Beclin-1 expression and autophagy induction. Meanwhile, knockdown of Beclin-1 by shRNA significantly sensitized salinomycin-induced OS cell lethality. In vivo, salinomycin administration suppressed U2OS xenograft tumor growth in severe combined immuno-deficient (SCID) mice, and its anti-tumor activity was dramatically potentiated with co-administration of the DNA-PKcs inhibitor NU7026. Together, these results suggest that DNA-PKcs could be a primary resistance factor of salinomycin in OS cells. DNA-PKcs inhibition or silence may thus significantly increase salinomycin's sensitivity in OS cells.

The anti-cancer activity of the mTORC1/2 dual inhibitor XL388 in preclinical osteosarcoma models.

In the present study, we investigated the activity of XL388, a novel mammalian target of rapamycin (mTOR) complex 1/2 (mTORC1/2) dual inhibitor, in preclinical osteosarcoma (OS) models. XL388 was cytotoxic, cytostatic and pro-apoptotic to multiple established OS cell lines and primary human OS cells. XL388 blocked mTORC1/2 activation and downregulated cyclin D1/B1 expressions in OS cells, leaving AKT Thr-308 phosphorylation un-affected. Intriguingly, AKT1 T308A mutation potentiated XL388-induced cytotoxicity in OS cells. XL388 activated cytoprotective autophagy in OS cells. Autophagy inhibition, either pharmacologically or genetically, augmented XL388-induced anti-OS activity. Further, XL388 oral administration inhibited U2OS xenografts growth in severe combined immuno-deficient (SCID) mice. Such activity was enhanced with co-administration of the autophagy inhibitor 3-methyladenine (3-MA). Similarly, Beclin-1-silenced U2OS xenografts were remarkably more sensitive to XL388. Thus, concurrent blockage of mTORC1/2 with XL388 may have therapeutic value for OS.

Autophagy inhibition sensitizes WYE-354-induced anti-colon cancer activity in vitro and in vivo.

Mammalian target of rapamycin (mTOR) complex 1 (mTORC1) and mTORC2 are frequently dysregulated in human colon cancers. In the present study, we evaluated the potential anti-colon cancer cell activity by a novel mTORC1/2 dual inhibitor WYE-354. We showed that WYE-354 was anti-survival and anti-proliferative when adding to primary (patient-derived) and established (HCT-116, HT-29, Caco-2, LoVo, and DLD-1 lines) colon cancer cells. In addition, WYE-354 treatment activated caspase-dependent apoptosis in the colon cancer cells. Mechanistically, WYE-354 blocked mTORC1 and mTORC2 activation. Meanwhile, it also induced autophagy activation in the colon cancer cells. Autophagy inhibitors (bafilomycin A1 and 3-methyladenine), or shRNA-mediated knockdown of autophagy elements (Beclin-1 and ATG-5), remarkably sensitized WYE-354-mediated anti-colon cancer cell activity in vitro. Further studies showed that WYE-354 administration inhibited HT-29 xenograft growth in severe combined immunodeficient (SCID) mice. Importantly, its activity in vivo was further potentiated with co-administration of the autophagy inhibitor 3-MA. Phosphorylations of Akt (Ser-473) and S6 were also decreased in WYE-354-treated HT-29 xenografts. Together, these pre-clinical results demonstrate the potent anti-colon cancer cell activity by WYE-354, and its activity may be further augmented with autophagy inhibition.

Activity of the novel dual phosphatidylinositol 3-kinase/mammalian target of rapamycin inhibitor NVP-BEZ235 against osteosarcoma.

Recent studies have identified that constitutively active phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signaling is an important feature of osteosarcoma, where it promotes cell proliferation, survival, and chemo-resistance. Here, we studied the therapeutic potential of NVP-BEZ235, a novel dual PI3K/mTOR dual inhibitor, on osteosarcoma cells in vivo and in vitro. NVP-BEZ235 was cytotoxic and cytostatic to a panel of osteosarcoma lines (MG-63, U2OS and SaOs-2), where it induce apoptosis and cell-cycle arrest. At the molecular level, NVP-BEZ235 inhibited PI3K-AKT-mTORC1 activation and downregulated cyclin D1/cyclin B1 expressions, while increasing MEK/Erk phosphorylation in osteosarcoma cells. MEK/Erk inhibitors PD98059 and MEK-162 increased NVP-BEZ235 activity on osteosarcoma cells. In vivo, oral NVP-BEZ235 inhibited U2OS xenograft in SCID mice, and its anti-tumor efficiency was further enhanced by MEK-162 co-administration. Taken together, our findings indicate that dual inhibition of PI3K and mTOR with NVP-BEZ235, either alone or in combination with MEK/Erk inhibitors, may be an efficient treatment for osteosarcoma.

Bufotalin-induced apoptosis in osteoblastoma cells is associated with endoplasmic reticulum stress activation.

The search for novel and more efficient chemo-agents against malignant osteoblastoma is important. In this study, we examined the potential anti-osteoblastoma function of bufotalin, and studied the underlying mechanisms. Our results showed that bufotalin induced osteoblastoma cell death and apoptosis in dose- and time-dependent manners. Further, bufotalin induced endoplasmic reticulum (ER) stress activation in osteoblastoma cells, the latter was detected by the induction of C/EBP homologous protein (CHOP), phosphorylation of inositol-requiring enzyme 1 (IRE1) and PKR-like endoplasmic reticulum kinase (PERK), as well as caspase-12 activation. Conversely, the ER stress inhibitor salubrinal, the caspase-12 inhibitor z-ATAD-fmk as well as CHOP depletion by shRNA significantly inhibited bufotalin-induced osteoblastoma cell death and apoptosis. Finally, by using a mice xenograft model, we demonstrated that bufotalin inhibited U2OS osteoblastoma cell growth in vivo. In summary, our results suggest that ER stress contributes to bufotalin-induced apoptosis in osteoblastoma cells. Bufotalin might be investigated as a novel anti-osteoblastoma agent.

[Morphologic and apoptotic changes of cervical posterior longitudinal ligament fibroblasts in response to in vitro mechanical stretch].

OBJECTIVE: To investigate the effect of mechanical stretch force on the morphologic and apoptotic changes of fibroblasts derived from the OPLL (ossification of posterior longitudinal ligaments) patients. METHODS: The third passage cells were collected and subjected to 10% elongations cyclic mechanical stretching for 6 h and 24 h with Flexercell 4000(TM) strain unit. Their morphologic changes were observed and the post-stretching apoptotic rates quantified by flow cytometer. The gene expressions of alkaline phosphatase (ALP), collagen types I (COL I) and osteocalcin (OC) were examined. RESULTS: The treated cells were arranged along the vertical direction of force. Stretch force led to a slight increase of apoptosis rate at 6 h and a significant increase of apoptosis rate at 24 h. No significant difference in cellular senescence was observed between control group and treated group. The mRNA expressions of ALP, COL I and OC were positively up-regulated by cyclic stretch at 24 h. CONCLUSION: Stretching force can affect the cellular morphology, promote the osteogenic differentiation and enhance the cellular apoptosis.