Polyploid giant cancer cells induced by Docetaxel exhibit a senescence phenotype with the expression of stem cell markers in ovarian cancer cells.

Docetaxel (Doc) plays a crucial role in clinical antineoplastic practice. However, it is continuously documented that tumors frequently develop chemoresistance and relapse, which may be related to polyploid giant cancer cells (PGCCs). The aim of this study was investigate the formation mechanism and biological behavior of PGCCs induced by Doc. Ovarian cancer cells were treated with Doc, and then the effect of Doc on cellular viability was evaluated by MTT assay and microscopic imaging analysis. The biological properties of PGCCs were further evaluated by Hoechst 33342 staining, cell cycle and DNA content assay, DNA damage response (DDR) signaling detection, ß-galactosidase staining, mitochondrial membrane potential detection, and reverse transcription-quantitative polymerase chain reaction. The results indicated that Doc reduced cellular viability; however, many cells were still alive, and were giant and polyploid. Doc increased the proportion of cells stayed in the G2/M phase and reduced the number of cells. In addition, the expression of γ-H2A.X was constantly increased after Doc treatment. PGCCs showed senescence-associated ß-galactosidase activity and an increase in the monomeric form of JC-1. The mRNA level of octamer-binding transcription factor 4 (OCT4) and krüppel-like factor 4 (KLF4) was significantly increased in PGCCs. Taken together, our results suggest that Doc induces G2/M cell cycle arrest, inhibits the proliferation and activates persistent DDR signaling to promote the formation of PGCCs. Importantly, PGCCs exhibit a senescence phenotype and express stem cell markers.

IL-1ß is involved in docetaxel chemoresistance by regulating the formation of polyploid giant cancer cells in non-small cell lung cancer.

Docetaxel (Doc) is a cornerstone of chemotherapy; however, treatment with Doc often and inevitably leads to drug resistance and the formation of polyploid giant cancer cells (PGCCs). In this study, we investigated the effect of Doc on non-small cell lung cancer to explore the role of PGCCs in drug resistance and the molecular mechanisms that regulate this resistance. We found that Doc induced G2/M cell cycle arrest and cell death in A549 and NCI-H1299 cells. However, many cells remained alive and became PGCCs by decreasing the expression of key regulatory proteins related to the cell cycle and proliferation. Notably, the PGCCs showed typical features of senescence, especially upregulation of p21 and p-histone H2A.X expression. Moreover, the mRNA level of IL-1ß in the senescence-associated secretory phenotype was increased significantly with the development of PGCCs. Inhibition of IL-1ß reduced the expression of p-histone H2A.X and promoted polyploidy to enhance the proapoptotic effect of Doc. Taken together, our results suggested that IL-1ß was involved in the formation of PGCCs and regulated the senescence of PGCCs, which contributed to drug resistance to Doc. Therefore, targeting IL-1ß in PGCCs may be a novel approach to overcome drug resistance.

Mesenchymal Stem Cells and their Derived Exosomes Promote Malignant Phenotype of Polyploid Non-Small-Cell Lung Cancer Cells through AMPK Signaling Pathway.

Chemotherapy is an important method for the treatment of non-small-cell lung cancer (NSCLC), but it can lead to side effects and polyploid cancer cells. The polyploid cancer cells can live and generate daughter cancer cells via budding. Mesenchymal stem cells (MSCs) are pluripotent stem cells with repair and regeneration functions and can resist tissue damage caused by tumor therapy. This study is aimed at investigating the effects of MSCs and their derived exosomes on the biological characteristics of polyploid NSCLC cells and the potential mechanisms. We found that MSC conditioned medium (CM), MSCs, and MSC-exosomes had no effect on cell proliferation of the polyploid A549 and H1299 cells. Compared with the control group, MSCs and MSC-exosomes significantly promoted epithelial mesenchymal transformation, cell migration, antiapoptosis, and autophagy in the polyploid A549 and H1299 by activating AMPK signaling pathway, but no significant changes were observed in MSC-CM treatment. These results revealed that MSCs and MSC-exosomes promoted malignant phenotype of polyploid NSCLC cells through the AMPK signaling pathway.

Down-regulation of PDGFRß suppresses invasion and migration in osteosarcoma cells by influencing epithelial-mesenchymal transition.

Osteosarcoma (OS) is the most common malignant bone tumor primarily influencing children and adults. Approximately one-fifth of patients have micrometastasis in the lungs when OS is diagnosed. Platelet-derived growth factor receptor (PDGFR) beta (PDGFRß) is a subtype of PDGFR. PDGFRß has been noted to be highly expressed in OS cell lines and patient specimens, and is associated with metastasis and poor prognosis of OS. However, mechanistic insights into the exact role of PDGFRß in OS pathogenesis and development are still lacking. Here we assessed the effects of PDGFRß on invasive and migratory abilities, such as the epithelial-mesenchymal transition and phosphatidylinositol 3-kinase (PI3K), Akt and mammalian target of rapamycin (mTOR) pathways in HOS cells. Depleting PDGFRß resulted in reduced migration of HOS cells in the small interfering RNA duplexes specific for the PDGFRß group compared with the mock and scramble-treated groups in Transwell invasion assays. Using wound-healing assays, we demonstrate the rate of wound healing in the PDGF-BB-stimulated group was higher compared with the mock-treated group. Western blot showed that down-regulation of PDGFRß decreased the expression of stromal phenotype markers and phosphorylation pathway proteins (PI3K, AKT and mTOR), but the epithelial phenotype marker was increased in HOS cells. Treating HOS cells with PDGF-BB revealed a treatment time-dependent increase of phosphorylated, but not total, PI3K, AKT and mTOR. Taken together, we suggest that PDGFRß plays an important role in OS invasion, migration and epithelial-mesenchymal transition by influencing the PI3K, Akt and mTOR pathways, hence highlighting PDGFRß as a potential therapeutic target for OS.

Influence of glucose transporter 1 activity inhibition on neuroblastoma in vitro.

Most cancer cells predominantly produce their energy through a high rate of glycolysis in the presence of abundant oxygen. Glycolysis has become a target of anticancer strategies. Previous researches showed that glucose transporter 1 (GLUT1) inhibitor is effective as anticancer agents. This study assessed the effects of the selective GLUT1 inhibitor WZB117 on regulation of neuroblastoma (NB) cell line SH-SY5Y viability, cell cycle and glycolysis in vitro. SH-SY5Y cells were grown and treated with WZB117 for up to 72 h and then subjected to cell viability, qRT-PCR, Western blot and flow cytometry analysis. Level of ATP and LDH was also analyzed. The result showed that WZB117 treatment reduced tumor cells viability, downregulated level of GLUT1 protein. Moreover, WZB117 treatment arrested tumor cells at the G0-G1 phase of the cell cycle, induced tumor cells to undergo necrosis instead of apoptosis. In addition, WZB117 treatment downregulated the levels of intracellular ATP, LDH and glycolytic enzymes. Thus, WZB117-induced GLUT1 inhibition suppressed tumor cell growth, induced cell cycle arrest and reduced glycolysis metabolites in NB cells in vitro. This study suggested that GLUT1 can be used as a potential therapeutic target for NB.

[Inhibiting the expression of glucose transporter 1 reduces the proliferation, invasion and migration of neuroblastoma cells].

Objective To study the effect of inhibiting the expression of glucose transporter 1 (GLUT1) in neuroblastoma cells on the proliferation, invasion and migration of tumor cells. Methods The specific small molecule inhibitor WZB117 was used to inhibit the expression of GLUT1 in neuroblastoma cells. The expression of GLUT1 mRNA was detected by real-time quantitative PCR; the expression of GLUT1 protein was detected by Western blotting; the ability of cell proliferation was detected by CCK-8 assay; the ability of cell invasion and migration were detected by TranswellTM invasion and migration assay, respectively. Results After treated with WZB117, the expression level of GLUT1 mRNA increased, while the protein expression level decreased in the neuroblastoma cells. Cell proliferation was inhibited, and the ability of cell invasion and migration were reduced. Conclusion Inhibiting the expression of GLUT1 in neuroblastoma cells might attenuate the malignant biological behaviors of tumor cells.

[Protein kinase A inhibitor H-89 blocks polyploidization of SP600125-induced CMK cells by regulating phosphorylation of ribosomal protein S6 kinase 1].

Objective To investigate the regulatory effect of post-translation modification of ribosomal protein S6 kinase 1 (S6K1) on the polyploidization of megakaryocytes. Methods SP600125, a c-Jun N-terminal kinase (JNK) inhibitor, and H-89, a cAMP-dependent protein kinase (PKA) inhibitor, were used to treat CMK cells separately or in combination. With propidium iodide (PI) to dye DNA in the treated cells, the relative DNA content was detected by flow cytometry, and then the DNA polyploidy was analyzed. The change of expression and phosphorylation of ribosomal protein S6 kinase 1 (S6K1), an important mammalian target of rapamycin (mTOR) downstream target molecule, was analyzed by Western blotting. Molecular docking study and kinase activity assay were performed to analyze the combination of H-89 with S6K1 and the effect of H-89 on the activity of S6K1 kinase. Results SP600125 induced CMK cell polyploidization in a time-dependent and dose-dependent manner. At the same time, it increased the phosphorylation of S6K1 at Thr421/Ser424 and decreased the phosphorylation of S6K1 at Thr389. H-89 not only blocked polyploidization, but also decreased the phosphorylation of S6K1 at Thr421/Ser424 and increased the phosphorylation of S6K1 at Thr389. Molecular docking and kinase activity assay showed that H-89 occupied the ATP binding sites of S6K1 and inhibited its activity. Noticeably, both H-89 and SP600125 inhibited the activity of PKA. Moreover, the two drugs further inhibited the activity of PKA when used together. Therefore, these data indicated that H-89 blocked the SP600125-induced polyploidization of CMK cells mainly by changing S6K1 phosphorylation state, rather than its inhibitory effect on PKA. Conclusion H-89 can block the polyploidization of SP600125-induced CMK cells by regulating S6K1 phosphorylation state.

[SP600125-induced polyploidization of megakaryocytic leukemia cell lines by ribosomal protein S6 kinase 1 depends on the degree of cell differentiation].

Objective To investigate regulatory role of ribosomal protein S6 kinase 1 (S6K1) in the polyploidization of different megakaryocytic leukemia cell lines at the different differentiation stages. Methods Megakaryocytic leukemia cell lines (Dami, Meg-01 and HEL cells) were induced towards polyploidization by SP600125, a c-Jun N-terminal kinase (JNK) inhibitor. The SP600125-inducing process was blocked by H-89, a cAMP-dependent protein kinase (PKA) inhibitor. The phenotype (CD41a, CD42a and CD42b) and DNA ploidy were detected by flow cytometry. The expression and phosphorylation of S6K1 and related proteins were detected by Western blotting. Results SP600125 induced polyploidization and increased the phosphorylation of eukaryotic initiation factor 4E binding protein 1 (4E-BP1) in Dami, Meg-01 and HEL cells. However, the effect of SP600125 on polyploidization of the three cell lines was different, with the strongest effect on Dami cells and the weakest on Meg-01 cells. Moreover, SP600125 increased the phosphorylation of S6K1 Thr421/Ser424 and decreased the phosphorylation of Thr389 in Dami cells. However, it only increased the phosphorylation of Thr389 in HEL cells and had no effect on the phosphorylation of S6K1 in Meg-01 cells. Interestingly, H-89 only partially blocked the polyploidization of Dami cells, although it decreased the phosphorylation of 4E-BP1 in all SP600125-induced three cell lines. Noticeably, H-89 decreased the phosphorylation of S6K1 Thr421/Ser424 and increased the phosphorylation of Thr389 in Dami cells. However, H-89 had no effect on the phosphorylation of Thr421/Ser424, although it increased the phosphorylation of Thr389 in Meg-01 and HEL cells. Phenotypic analysis showed that the three cell lines were at different levels of differentiation in megakaryocytic lineage, with the highest differentiation in Dami and the lowest in Meg-01 cells. Conclusion SP600125-induced polyploidization of megakaryocytic leukemia cell lines is dependent on the effect of SP600125 on phosphorylation of S6K1 in cell lines at the different differentiation stages.

Phosphorylation of ribosomal protein S6 kinase 1 at Thr421/Ser424 and dephosphorylation at Thr389 regulates SP600125-induced polyploidization of megakaryocytic cell lines.

Megakaryocytes (MKs) are one of the few cell types that become polyploid; however, the mechanisms by which these cells are designated to become polyploid are not fully understood. In this investigation, we successfully established two relatively synchronous polyploid cell models by inducing Dami and CMK cells with SP600125. We found that SP600125 induced the polyploidization of Dami and CMK cells, concomitant with the phosphorylation of ribosomal protein S6 kinase 1 (S6K1) at Thr421/Ser424 and dephosphorylation at Thr389. The polyploidization was partially blocked by H-89, a cAMP-dependent protein kinase (PKA) inhibitor, through direct binding to S6K1, leading to dephosphorylation at Thr421/Ser424 and phosphorylation at Thr389, independent of PKA. Overexpression of a rapamycin-resistant mutant of S6K1 further enhanced the inhibitory effect of LY294002 on the SP600125-induced polyploidization of Dami and CMK cells. SP600125 also induced the polyploidization of Meg-01 cells, which are derived from a patient with chronic myelogenous leukemia, without causing a significant change in S6K1 phosphorylation. Additionally, SP600125 induced the polyploidization of HEL cells, which are derived from a patient with erythroleukemia, and phosphorylation at Thr389 of S6K1 was detected. However, the polyploidization of both Meg-01 cells and HEL cells as a result of SP600125 treatment was lower than that of SP600125-induced Dami and CMK cells, and it was not blocked by H-89 despite the increased phosphorylation of S6K1 at Thr389 in both cell lines in response to H-89. Given that the Dami and CMK cell lines were derived from patients with acute megakaryocytic leukemia (AMKL) and expressed high levels of platelet-specific antigens, our data suggested that SP600125-induced polyploidization is cell-type specific, that these cell lines were more differentiated, and that phosphorylation at Thr421/Ser424 and dephosphorylation at Thr389 of S6K1 may play an important role in the SP600125-induced polyploidization of these cell lines synergistically with other signaling pathways.