Efficacy of an anti-cancer strategy targeting SET in canine osteosarcoma

Tenuigenin inhibits osteosarcoma growth via CIP2A/PP2A/NF-κB axis

BACKGROUND

Polygala tenuifolia and its active components have been revealed to possess anti-tumor activities. However, the role of Tenuigenin (TEN), a bioactive ingredient from Polygala tenuifolia, in tumors such as osteosarcoma (OS) remains unclear. The present research intended to explore the efficacy and underlying mechanism of TEN on OS.

METHODS

OS cells were administrated with different concentrations of TEN. Cell viability, proliferation, invasion, and migration were assessed with CCK-8 assay, colony formation assay, transwell assay, and wound healing assay, respectively. Protein and mRNA levels were determined with western blot and qRT-PCR, while protein phosphatase 2A (PP2A) activity was tested with PP2A phosphatase assay kit. The interaction between PP2A and cancerous inhibitor of protein phosphatase 2A (CIP2A) or nuclear factor kappaB (NF-κB) signaling was detected using co-immunoprecipitation. p-p65 expression in the nucleus was determined with immunofluorescence. The efficacy of TEN in vivo was also explored in a xenograft tumor model. Immunohistochemistry was performed to detect CIP2A and Ki67 in mice.

RESULTS

TEN treatment or CIP2A depletion repressed cell viability, proliferation, invasion, and migration in OS cells. Additionally, TEN reduced CIP2A, increased PP2A activity, and inactivated NF-κB signaling. PP2A directly interacted with CIP2A or NF-κB signaling, and PP2A inhibition reversed CIP2A knockdown-induced repression of NF-κB signaling. CIP2A overexpression overturned the efficacy of TEN, which was reversed by NF-κB inhibition. TEN decreased CIP2A, elevated PP2A activity, inactivated NF-κB signaling, and inhibited tumor growth in vivo, which was antagonized by CIP2A overexpression.

CONCLUSION

TEN suppressed OS growth via CIP2A/PP2A/NF-κB axis, indicating that it would be a novel drug for treating OS.

PP2A inhibitor SET promotes mTORC1 and Bmi1 signaling through Akt activation and maintains the colony-formation ability of cancer cells

Protein phosphatase 2A (PP2A) is an essential tumor suppressor, with its activity often hindered in cancer cells by endogenous PP2A inhibitory proteins like SE translocation (SET). SET/PP2A axis plays a pivotal role in the colony-formation ability of cancer cells and the stabilization of c-Myc and E2F1 proteins implicated in this process. However, in osteosarcoma cell line HOS, SET knock-down (KD) suppresses the colony-formation ability without affecting c-Myc and E2F1. This study aimed to unravel the molecular mechanism through which SET enhances the colony-formation ability of HOS cells and determine if it is generalized to other cancer cells. Transcriptome analysis unveiled that SET KD suppressed mTORC1 signaling. SET KD inhibited Akt phosphorylation, an upstream kinase for mTORC1. PP2A inhibitor blocked SET KD-mediated decrease in phosphorylation of Akt and a mTORC1 substrate p70S6K. A constitutively active Akt restored decreased colony-formation ability by SET KD, indicating the SET/PP2A/Akt/mTORC1 axis. Additionally, enrichment analysis highlighted that Bmi-1, a polycomb group protein, is affected by SET KD. SET KD decreased Bmi-1 protein by Akt inhibition but not by mTORC1 inhibition, and exogenous Bmi-1 expression rescued the reduced colony formation by SET KD. Four out of eight cancer cell lines exhibited decreased Bmi-1 by SET KD. Further analysis of these cell lines revealed that Myc activity plays a role in SET KD-mediated Bmi-1 degradation. These findings provide new insights into the molecular mechanism of SET-regulated colony-formation ability, which involved Akt-mediated activation of mTORC1/p70S6K and Bmi-1 signaling.

Characterizing the metabolic role of STAT3 in canine osteosarcoma

Signal transducer and activator of transcription 3 (STAT3) dysregulation has been characterized in canine OS, with previous data suggesting that constitutive STAT3 activation contributes to survival and proliferation in OS cell lines in vitro. Recently, the contribution of STAT3 to tumour metabolism has been described across several tumour histologies, and understanding the metabolic implications of STAT3 loss may elucidate novel therapeutic approaches with synergistic activity. The objective of this work was to characterize metabolic benchmarks associated with STAT3 loss in canine OS. STAT3 expression and activation was evaluated using western blotting in canine OS cell lines OSCA8 and Abrams. STAT3 was deleted from these OS cell lines using CRISPR-Cas9, and the effects on proliferation, invasion and metabolism (respirometry, intracellular lactate) were determined. Loss of STAT3 was associated with decreased basal and compensatory glycolysis in canine OS cell lines, without modulation of cellular proliferation. Loss of STAT3 also resulted in diminished invasive capacity in vitro. Interestingly, the absence of STAT3 did not impact sensitivity to doxorubicin in vitro. Our data demonstrate that loss of STAT3 modulates features of aerobic glycolysis in canine OS impacting capacities for cellular invasions, suggesting a role for this transcription factor in metastasis.

Review: NF-kB activation in canine cancer

Spontaneous tumors in dogs share several environmental, epidemiologic, biologic, clinical and molecular features with a wide variety of human cancers, making this companion animal an attractive model. Nuclear factor kappa B (NF-kB) transcription factor overactivation is common in several human cancers, and there is evidence that similar signaling aberrations also occur in canine cancers including lymphoma, leukemia, hemangiosarcoma, mammary cancer, melanoma, glioma, and prostate cancer. This review provides an overview of NF-kB signaling biology, both in health and in cancer development. It also summarizes available evidence of aberrant NF-kB signaling in canine cancer, and reviews antineoplastic compounds that have been shown to inhibit NF-kB activity used in various types of canine cancers. Available data suggest that dogs may be an excellent model for human cancers that have overactivation of NF-kB.

Epigenetic Mechanisms in Canine Cancer

A plethora of data has highlighted the role of epigenetics in the development of cancer. Initiation and progression of different cancer types are associated with a variety of changes of epigenetic mechanisms, including aberrant DNA methylation, histone modifications, and miRNA expression. At the same time, advances in the available epigenetic tools allow to investigate and reverse these epigenetic changes and form the basis for the development of anticancer drugs in human oncology. Although human and canine cancer shares several common features, only recently that studies emerged investigating the epigenetic landscape in canine cancer and applying epigenetic modulators to canine cancer. This review focuses on the existing studies involving epigenetic changes in different types of canine cancer and the use of small-molecule inhibitors in canine cancer cells.