Adherence of Plasmodium falciparum infected erythrocytes to CHO-745 cells and inhibition of binding by protein A in the presence of human serum

Adhesion of erythrocytes infected with the malaria parasite Plasmodium falciparum to human host receptors is a process associated with severe malarial pathology. A number of in vitro cell lines are available as models for these adhesive processes, including Chinese hamster ovary (CHO) cells which express the placental adhesion receptor chondroitin-4-sulphate (CSA) on their surface. CHO-745 cells, a glycosaminoglycan-negative mutant CHO cell line lacking CSA and other reported P. falciparum adhesion receptors, are often used for recombinant expression of host receptors and for receptor binding studies. In this study we show that P. falciparum-infected erythrocytes can be easily selected for adhesion to an endogenous receptor on the surface of CHO-745 cells, bringing into question the validity of using these cells as a tool for P. falciparum adhesin expression studies. The adhesive interaction between CHO-745 cells and parasitized erythrocytes described here is not mediated by the known P. falciparum adhesion receptors CSA, CD36, or ICAM-1. However, we found that CHO-745-selected parasitized erythrocytes bind normal human IgM and that adhesion to CHO-745 cells is inhibited by protein A in the presence of serum, but not in its absence, indicating a non-specific inhibitory effect. Thus, protein A, which has been used as an inhibitor for a recently described interaction between infected erythrocytes and the placenta, may not be an appropriate in vitro inhibitor for understanding in vivo adhesive interactions. (c) 2005 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.

Antisense-mediated inhibition of the plasma membrane Calcium-ATPase suppresses proliferation of MCF-7 cells

Alterations in Ca2+ signaling may contribute to tumorigenesis and the mechanism of action of some anticancer drugs. The plasma membrane calcium-ATPase (PMCA) is a crucial controller of intracellular Ca2+ signaling. Altered PMCA expression occurs in the mammary gland during lactation and in breast cancer cell lines. Despite this, the consequences of PMCA inhibition in breast cancer cell lines have not been investigated. In this work, we used Tet-off PMCA antisense-expressing MCF-7 cells to assess the effects of PMCA inhibition in a human breast cancer cell line. At a level of PMCA inhibition that did not completely prevent PMCA-mediated Ca2+ efflux and did not induce cell death, a dramatic inhibition of cellular proliferation was observed. Fluorescence-activated cell sorting analysis indicated that PMCA antisense involves changes in cell cycle kinetics but not cell cycle arrest. We concluded that modulation of PMCA has important effects in regulating the proliferation of human breast cancer MCF-7 cells.