Cell cycle arrest and the induction of apoptosis in pancreatic cancer cells exposed to adenosine triphosphate in vitro

Extracellular ATP Induced S-Phase Cell Cycle Arrest via P2Y Receptor-Activated ERK Signaling in Poorly Differentiated Oral Squamous Cell Carcinoma SAS Cells

Extracellular ATP in the tumor microenvironment exhibits either pro- or antitumor effect via interaction with P2Y receptors, but the intracellular signaling and functional roles of P2Y receptors in oral squamous cell carcinoma (OSCC) are unclear. We aimed to study the effect of ATP on OSCC cell lines and the potential mechanisms involved. Through GEPIA dataset analysis, high expression levels of mRNA encoding P2Y receptors, the ATP-induced G protein-coupled receptors, were associated with better overall patient survival in head and neck squamous cell carcinoma. qPCR analysis showed that the poorly differentiated OSCC SAS cell line, had higher P2RY1 expression level compared to the well-differentiated H103 and H376 cell lines. Western blotting and flow cytometry analyses revealed that ATP phosphorylated ERK and elevated intracellular calcium signaling in all tested cell lines. A significant S-phase cell cycle arrest was observed in SAS, and preincubation with the MEK inhibitor PD0325901 reversed the ATP-induced S-phase arrest. We further demonstrated that ATP induced a slight reduction in cell count and colony formation yet significant apoptosis in SAS. Overall, we postulate that the ATP-induced S-phase arrest effect in SAS cells may be regulated through P2Y receptor-mediated ERK signaling, thus suggesting a potential antitumor effect of ATP via interaction with its distinct profile of P2Y receptors.

Breast Cancer Cell-Derived Adenosine Enhances Generation and Suppressor Function of Human Adaptive Regulatory T Cells

Introduction: Adaptive regulatory T cells (Tr1) are induced in the periphery by environmental stimuli. CD73 expression and adenosine (ADO) production by tumor cells may influence Tr1 generation and their immunosuppressive activity. Material and Methods: Tr1 were generated in co-cultures of CD4+CD25neg T cells, autologous immature dendritic cells (iDC), and irradiated ADO-producing CD73+ or non-producing CD73neg breast cancer (BrCa) cell lines (TU). The expression of ectonucleotidases and other surface markers on Tr1 was determined by flow cytometry. Tr1-mediated suppression of proliferation was evaluated in CFSE-based assays. Luciferase-based ATP detection assays and mass spectrometry were used to measure ATP hydrolysis and ADO levels. Cytokine levels were measured by ELISA or Luminex. CD73 expression on tumor cells or T cells in TU tissues was assessed by immunofluorescence. Results: CD73+ TU induced higher numbers of Tr1 cells (p < 0.01) than CD73neg TU. Tr1TU73+ hydrolyzed more exogenous ATP, produced more ADO, and mediated higher suppression than Tr1TU73neg (p < 0.05 for all). ARL67156, an ectonucleotidase inhibitor, and ZM241385, A2A receptor antagonist, reduced suppression of proliferation mediated by Tr1TU73+ cells (p < 0.01). Basal-like primary BrCa cells expressed higher levels of ectonucleotidases and induced more Tr1 than less aggressive primary luminal-like BrCa. Conclusion: BrCa producing ADO (CD73+ TU) favor the induction of Tr1, which expresses CD39 and CD73, hydrolyzes ATP to ADO, and effectively suppresses anti-tumor immunity.

Inhibitory effects of extracellular adenosine triphosphate on growth of esophageal carcinoma cells

AIM: To study the growth inhibitory effects of ATP on TE-13 human squamous esophageal carcinoma cells in vitro.

METHODS: MTT assay was used to determine the inhibition of proliferation of ATP or adenosine (ADO) on TE-13 cell line. The morphological changes of TE-13 cells induced by ATP or ADO were observed under fluorescence light microscope by acridine orange (AO)/ethidium bromide (EB) double stained cells. The internucleosomal fragmentation of genomic DNA was detected by agarose gel electrophoresis. The apoptotic rate and cell cycle after treatment with ATP or ADO were determined by flow cytometry.

RESULTS: ATP and ADO produced inhibitory effects on TE-13 cells at the concentration between 0.01 and 1.0 mmol/L. The IC50 of TE-13 cells exposed to ATP or ADO for 48 and 72 h was 0.71 or 1.05, and 0.21 or 0.19 mmol/L, respectively. The distribution of cell cycle phase and proliferation index (PI) value of TE-13 cells changed, when being exposed to ATP or ADO at the concentrations of 0.01, 0.1, and 1 mmol/L for 48 h. ATP and ADO inhibited the cell proliferation by changing the distribution of cell cycle phase via either G0/G1 phase (ATP or ADO, 1 mmol/L) or S phase (ATP, 0.1 mmol/L) arrest. Under light microscope, the tumor cells exposed to 0.3 mmol/L ATP or ADO displayed morphological changes of apoptosis. A ladder-like pattern of DNA fragmentation was obtained from TE-13 cells treated with 0.1-1 mmol/L ATP or ADO in agarose gel electrophoresis. ATP and ADO induced apoptosis of TE-13 cells in a dose-dependent manner at the concentration between 0.03 and 1 mmol/L. The maximum apoptotic rate of TE-13 cells exposed to ATP or ADO for 48 h was 16.63% or 16.9%, respectively.

CONCLUSION: ATP and ADO inhibit cell proliferation, arrest cell cycle, and induce apoptosis of TE-13 cell line.