Toxoplasma GRA16 Inhibits NF-κB Activation through PP2A-B55 Upregulation in Non-Small-Cell Lung Carcinoma Cells
Seung-Hwan Seo1, Sang-Gyun Kim1, Ji-Hun Shin1
1Department of Tropical Medicine and Parasitology, Seoul National University College of Medicine, and Institute of Endemic Diseases, Seoul 03080, Korea.
Abstract:
Nuclear factor kappa B (NF-κB) activation is a well-known mechanism by which chemoresistance to anticancer agents is reported. It is well-known that irinotecan as a chemotherapeutic drug against non-small-cell lung carcinoma (NSCLC) has limited anticancer effect due to NF-κB activation. In this study, we propose the novel role of GRA16, a dense granule protein of Toxoplasma gondii, as an anticancer agent to increase the effectiveness of chemotherapy via the inhibition of NF-κB activation. To demonstrate this, H1299 cells were stably transfected with GRA16. The anticancer effects of GRA16 were demonstrated as a reduction in tumor size in a mouse xenograft model. GRA16 directly elevated B55 regulatory subunit of protein phosphatase 2A (PP2A-B55) expression in tumor cells, thereby decreasing GWL protein levels and ENSA phosphorylation. This cascade, in turn, induced PP2A-B55 activation and suppressed AKT/ERK phosphorylation and cyclin B1 levels, suggesting reduced cell survival and arrested cell cycle. Moreover, PP2A-B55 activation and AKT phosphorylation inhibition led to NF-κB inactivation via the reduction in inhibitory kappa B kinase beta (IKKβ) levels, de-phosphorylation of inhibitor of kappa B alpha (IκBα), and reduction in the nuclear transit of NF-κB p65. Furthermore, this molecular mechanism was examined under irinotecan treatment. The PP2A-B55/AKT/NF-κB p65 pathway-mediated anticancer effects were only induced in the presence of GRA16, but not in the presence of irinotecan. Moreover, GRA16 synergistically promoted the anticancer effects of irinotecan via the induction of the sub-G1 phase and reduction of cell proliferation. Collectively, irinotecan and GRA16 co-treatment promotes the anticancer effects of irinotecan via NF-κB inhibition and cell cycle arrest induced by GRA16, subsequently increasing the chemotherapeutic effect of irinotecan to NSCLC cells via NF-κB inhibition.
Insights
Toxoplasma gondii GRA16 protein enhances chemotherapy for non-small-cell lung carcinoma (NSCLC) by inhibiting Nuclear factor kappa B (NF-κB) activation. This novel agent synergizes with irinotecan, reducing tumor growth and increasing treatment effectiveness.
Area of Science:
- Molecular Biology
- Oncology
- Parasitology
Background:
- Nuclear factor kappa B (NF-κB) activation contributes to chemoresistance in non-small-cell lung carcinoma (NSCLC).
- Irinotecan efficacy against NSCLC is limited by NF-κB activation.
Purpose of the Study:
- To investigate the novel anticancer role of GRA16, a dense granule protein from *Toxoplasma gondii*, in overcoming chemoresistance.
- To determine if GRA16 can enhance irinotecan chemotherapy effectiveness in NSCLC by inhibiting NF-κB activation.
Main Methods:
- Stable transfection of H1299 cells with GRA16.
- Evaluation of anticancer effects in a mouse xenograft model.
- Analysis of the molecular pathway involving protein phosphatase 2A regulatory subunit B55 (PP2A-B55), AKT, ERK, and NF-κB signaling.
Main Results:
- GRA16 administration reduced tumor size and elevated PP2A-B55 expression, leading to suppressed AKT/ERK phosphorylation and cell cycle arrest.
- GRA16 inactivated NF-κB by reducing IKKβ, de-phosphorylating IκBα, and inhibiting NF-κB p65 nuclear translocation.
- GRA16 synergistically enhanced irinotecan's anticancer effects by inducing sub-G1 phase, reducing cell proliferation, and inhibiting NF-κB.
Conclusions:
- GRA16 acts as a novel anticancer agent by activating the PP2A-B55/AKT pathway, leading to NF-κB inhibition and cell cycle arrest.
- GRA16 significantly potentiates the chemotherapeutic efficacy of irinotecan in NSCLC models.
- GRA16 represents a promising strategy to overcome irinotecan resistance in NSCLC.
