Daneth L. Marcial

Altered purinergic receptor‐Ca2+ signaling associated with hypoxia‐induced epithelial‐mesenchymal transition in breast cancer cells

Hypoxia is a feature of the microenvironment of many cancers and can trigger epithelial‐mesenchymal transition (EMT), a process by which cells acquire a more invasive phenotype with enriched survival. A remodeling of adenosine 5′‐triphosphate (ATP)‐induced Ca2+ signaling via purinergic receptors is associated with epidermal growth factor (EGF)‐induced EMT in MDA‐MB‐468 breast cancer cells. Here, we assessed ATP‐mediated Ca2+ signaling in a model of hypoxia‐induced EMT in MDA‐MB‐468 cells. Like EGF, hypoxia treatment (1% O2) was also associated with a significant reduction in the sensitivity of MDA‐MB‐468 cells to ATP (EC50 of 0.5 μM for normoxic cells versus EC50 of 5.8 μM for hypoxic cells). Assessment of mRNA levels of a panel of P2X and P2Y purinergic receptors following hypoxia revealed a change in levels of a suite of purinergic receptors. P2X4, P2X5, P2X7, P2Y1 and P2Y11 mRNAs decreased with hypoxia, whereas P2Y6 mRNA increased. Up‐regulation of P2Y6 was a common feature of both growth factor‐ and hypoxia‐induced models of EMT. P2Y6 levels were also significantly increased in basal‐like breast tumors compared to other subtypes and breast cancer patients with higher P2Y6 levels showed reduced overall survival rates. P2Y6 siRNA‐mediated silencing and the P2Y6 pharmacological inhibitor MRS2578 reduced hypoxia‐induced vimentin protein expression in MDA‐MB‐468 cells. P2Y6 inhibition also reduced the migration of mesenchymal‐like MDA‐MB‐231 breast cancer cells. The up‐regulation of P2Y6 appears to be a common feature of the mesenchymal phenotype of breast cancer cells and inhibition of this receptor may represent a novel therapeutic target in breast cancer metastasis.

The Eukaryotic Elongation Factor 1A Is Critical for Genome Replication of the Paramyxovirus Respiratory Syncytial Virus

The eukaryotic translation factor eEF1A assists replication of many RNA viruses by various mechanisms. Here we show that down-regulation of eEF1A restricts the expression of viral genomic RNA and the release of infectious virus, demonstrating a biological requirement for eEF1A in the respiratory syncytial virus (RSV) life cycle. The key proteins in the replicase/transcriptase complex of RSV; the nucleocapsid (N) protein, phosphoprotein (P) and matrix (M) protein, all associate with eEF1A in RSV infected cells, although N is the strongest binding partner. Using individually expressed proteins, N, but not P or M bound to eEF1A. This study demonstrates a novel interaction between eEF1A and the RSV replication complex, through binding to N protein, to facilitate genomic RNA synthesis and virus production.

The calcium pump plasma membrane Ca(2+)-ATPase 2 (PMCA2) regulates breast cancer cell proliferation and sensitivity to doxorubicin

Regulation of Ca2+ transport is vital in physiological processes, including lactation, proliferation and apoptosis. The plasmalemmal Ca2+ pump isoform 2 (PMCA2) a calcium ion efflux pump, was the first protein identified to be crucial in the transport of Ca2+ ions into milk during lactation in mice. In these studies we show that PMCA2 is also expressed in human epithelia undergoing lactational remodeling and also report strong PMCA2 staining on apical membranes of luminal epithelia in approximately 9% of human breast cancers we assessed. Membrane protein expression was not significantly associated with grade or hormone receptor status. However, PMCA2 mRNA levels were enriched in Basal breast cancers where it was positively correlated with survival. Silencing of PMCA2 reduced MDA-MB-231 breast cancer cell proliferation, whereas silencing of the related isoforms PMCA1 and PMCA4 had no effect. PMCA2 silencing also sensitized MDA-MB-231 cells to the cytotoxic agent doxorubicin. Targeting PMCA2 alone or in combination with cytotoxic therapy may be worthy of investigation as a therapeutic strategy in breast cancer. PMCA2 mRNA levels are also a potential tool in identifying poor responders to therapy in women with Basal breast cancer.

Oncosis and apoptosis induction by activation of an overexpressed ion channel in breast cancer cells

The critical role of calcium signalling in processes related to cancer cell proliferation and invasion has seen a focus on pharmacological inhibition of overexpressed ion channels in specific cancer subtypes as a potential therapeutic approach. However, despite the critical role of calcium in cell death pathways, pharmacological activation of overexpressed ion channels has not been extensively evaluated in breast cancer. Here we define the overexpression of transient receptor potential vanilloid 4 (TRPV4) in a subgroup of breast cancers of the basal molecular subtype. We also report that pharmacological activation of TRPV4 with GSK1016790A reduced viability of two basal breast cancer cell lines with pronounced endogenous overexpression of TRPV4, MDA-MB-468 and HCC1569. Pharmacological activation of TRPV4 produced pronounced cell death through two mechanisms: apoptosis and oncosis in MDA-MB-468 cells. Apoptosis was associated with PARP-1 cleavage and oncosis was associated with a rapid decline in intracellular ATP levels, which was a consequence of, rather than the cause of, the intracellular ion increase. TRPV4 activation also resulted in reduced tumour growth in vivo. These studies define a novel therapeutic strategy for breast cancers that overexpress specific calcium permeable plasmalemmal ion channels with available selective pharmacological activators.