Aquaporin expression in breast cancer and their involvement in bleb formation, cell motility and invasion in endocrine resistant variant cells

Clinical value and molecular mechanism of AQGPs in different tumors

Aquaglyceroporins (AQGPs), including AQP3, AQP7, AQP9, and AQP10, are transmembrane channels that allow small solutes across biological membranes, such as water, glycerol, H₂O₂, and so on. Increasing evidence suggests that they play critical roles in cancer. Overexpression or knockdown of AQGPs can promote or inhibit cancer cell proliferation, migration, invasion, apoptosis, epithelial-mesenchymal transition and metastasis, and the expression levels of AQGPs are closely linked to the prognosis of cancer patients. Here, we provide a comprehensive and detailed review to discuss the expression patterns of AQGPs in different cancers as well as the relationship between the expression patterns and prognosis. Then, we elaborate the relevance between AQGPs and malignant behaviors in cancer as well as the latent upstream regulators and downstream targets or signaling pathways of AQGPs. Finally, we summarize the potential clinical value in cancer treatment. This review will provide us with new ideas and thoughts for subsequent cancer therapy specifically targeting AQGPs.

Novel Ion Channel Targets and Drug Delivery Tools for Controlling Glioblastoma Cell Invasiveness

Comprising more than half of all brain tumors, glioblastoma multiforme (GBM) is a leading cause of brain cancer-related deaths worldwide. A major clinical challenge is presented by the capacity of glioma cells to rapidly infiltrate healthy brain parenchyma, allowing the cancer to escape control by localized surgical resections and radiotherapies, and promoting recurrence in other brain regions. We propose that therapies which target cellular motility pathways could be used to slow tumor dispersal, providing a longer time window for administration of frontline treatments needed to directly eradicate the primary tumors. An array of signal transduction pathways are known to be involved in controlling cellular motility. Aquaporins (AQPs) and voltage-gated ion channels are prime candidates as pharmacological targets to restrain cell migration in glioblastoma. Published work has demonstrated AQPs 1, 4 and 9, as well as voltage-gated potassium, sodium and calcium channels, chloride channels, and acid-sensing ion channels are expressed in GBM and can influence processes of cell volume change, extracellular matrix degradation, cytoskeletal reorganization, lamellipodial and filopodial extension, and turnover of cell-cell adhesions and focal assembly sites. The current gap in knowledge is the identification of optimal combinations of targets, inhibitory agents, and drug delivery systems that will allow effective intervention with minimal side effects in the complex environment of the brain, without disrupting finely tuned activities of neuro-glial networks. Based on published literature, we propose that co-treatments using AQP inhibitors in addition to other therapies could increase effectiveness, overcoming some limitations inherent in current strategies that are focused on single mechanisms. An emerging interest in nanobodies as drug delivery systems could be instrumental for achieving the selective delivery of combinations of agents aimed at multiple key targets, which could enhance success in vivo.

Inhibition of aquaporins as a potential adjunct to breast cancer cryotherapy

Cryoablation is an emerging type of treatment for cancer. The sensitization of tumors using cryosensitizing agents prior to treatment enhances ablation efficiency and may improve clinical outcomes. Water efflux, which is regulated by aquaporin channels, contributes to cancer cell damage achieved through cryoablation. An increase in aquaporin (AQP) 3 is cryoprotective, whereas its inhibition augments cryodamage. The present study aimed to investigate aquaporin (AQP1, AQP3 and AQP5) gene expression and cellular localization in response to cryoinjury. Cultured breast cancer cells (MDA-MB-231 and MCF-7) were exposed to freezing to induce cryoinjury. RNA and protein extracts were then analyzed using reverse transcription-quantitative PCR and western blotting, respectively. Localization of aquaporins was studied using immunocytochemistry. Additionally, cells were transfected with small interfering RNA to silence aquaporin gene expression and cell viability was assessed using the Sulforhodamine B assay. Cryoinjury did not influence gene expression of AQPs, except for a 4-fold increase of AQP1 expression in MDA-MD-231 cells. There were no clear differences in AQP protein expression for either cell lines upon exposure to frozen and non-frozen temperatures, with the exception of fainter AQP5 bands for non-frozen MCF-7 cells. The exposure of cancer cells to freezing temperatures altered the localization of AQP1 and AQP3 proteins in both MCF-7 and MDA-MD-231 cells. The silencing of AQP1, AQP3 and AQP5 exacerbated MDA-MD-231 cell damage associated with freezing compared with control siRNA. This was also observed with AQP3 and AQP5 silencing in MCF-7 cells. Inhibition of aquaporins may potentially enhance cryoinjury. This cryosensitizing process may be used as an adjunct to breast cancer cryotherapy, especially in the border area targeted by cryoablation where freezing temperatures are not cold enough to induce cellular damage.

Aquaglyceroporin-3's Expression and Cellular Localization Is Differentially Modulated by Hypoxia in Prostate Cancer Cell Lines

Aquaporins are required by cells to enable fast adaptation to volume and osmotic changes, as well as microenvironmental metabolic stimuli. Aquaglyceroporins play a crucial role in supplying cancer cells with glycerol for metabolic needs. Here, we show that AQP3 is differentially expressed in cells of a prostate cancer panel. AQP3 is located at the cell membrane and cytoplasm of LNCaP cell while being exclusively expressed in the cytoplasm of Du145 and PC3 cells. LNCaP cells show enhanced hypoxia growth; Du145 and PC3 cells display stress factors, indicating a crucial role for AQP3 at the plasma membrane in adaptation to hypoxia. Hypoxia, both acute and chronic affected AQP3′s cellular localization. These outcomes were validated using a machine learning classification approach of the three cell lines and of the six normoxic or hypoxic conditions. Classifiers trained on morphological features derived from cytoskeletal and nuclear labeling alongside corresponding texture features could uniquely identify each individual cell line and the corresponding hypoxia exposure. Cytoskeletal features were 70–90% accurate, while nuclear features allowed for 55–70% accuracy. Cellular texture features (73.9% accuracy) were a stronger predictor of the hypoxic load than the AQP3 distribution (60.3%).