A three-dimensional microenvironment alters CD73 expression in cervical cancer

Stem-like cells (CSCs) have a tumour-initiating capacity and play critical role in tumour metastasis, relapse and resistance to therapy. The ectoenzyme CD73, encoded by the NT5E gene, which catalyses the hydrolysis of AMP into adenosine, has been associated to an immunosuppressive tumour microenvironment, tumour cell adhesion and migration. Therefore, we investigated the expression and activity of CD73 in sphere-forming cells from cervical cancer in comparison to monolayer cells in vitro. In addition, in silico analysis was performed to determine the expression of CD73 and other members of purinergic signalling in CSC-like population derived from different tumour types in comparison to monolayer cells. CD73 protein expression levels and functionality in SiHa cells were analysed by flow cytometry and enzymatic assay, respectively. In silico investigation was performed through the analysis of seven datasets from different tumour types using GEO database. In vitro analysis showed a decreased CD73 protein expression and enzymatic activity in cervical spheres, when compared to monolayers. In addition, when sphere-derived cells are re-plated as monolayer culture, the CD73 expression and activity are restored. Supporting the in vitro results, in silico analysis showed that three-dimensional spheres derived from cervical, thyroid and breast cancer presented decreased expression of CD73, when compared to their adherent counterparts. The decreased expression of CD73 in sphere-derived cells or CSC-enriched population reinforce its important role in cell adhesion, tumour spreading ability and metastasis, suggesting CD73 as potential target to be further investigated in cervical cancer.