Inhibition of the biologic response to insulin-like growth factor I in MCF-7 breast cancer cells by a new monoclonal antibody to the insulin-like growth factor-I receptor. The importance of receptor down-regulation.

We developed a mouse monoclonal antibody (4G11) against insulin-like growth factor I receptor by immunizing mice with mouse embryo fibroblasts overexpressing the human insulin-like growth factor-I receptor. Not only did the 4G11 antibody inhibit the binding of [ (125)I]insulin-like growth factor-I to the fibroblast receptor, but 4G11 antibody also potently down-regulated the insulin-like growth factor-I receptor. 4G11 Fab fragment inhibited ligand binding, but did not down-regulate the receptor, suggesting that receptor aggregation is required for down-regulation. 4G11 antibody also down-regulated the receptor in MCF-7 breast cancer cells, a panel of colon cancer cells and MG-63 osteosarcoma cells. Receptor recovery in MCF-7 cells after down-regulation by 4G11 antibody was slow, requiring 32 - 48 h for full recovery. Receptor down-regulation in MCF-7 cells by 4G11 antibody was confirmed by FACS analysis of intact and permeabilized cells. In contrast to 4G11 antibody, insulin-like growth factor-I did not down-regulate the receptor in MCF-7 cells. Down-regulation of the receptor by 4G11 antibody in MCF-7 cells resulted in inhibition of Akt and MAPK activation by insulin-like growth factor-I. We conclude that the ability of a monoclonal antibody to down-regulate the receptor may be an important antibody property in targeting the insulin-like growth factor-I receptor for the treatment of certain cancers.     

Mapping a common interaction site used by Plasmodium falciparum Duffy binding-like domains to bind diverse host receptors

The Duffy binding-like (DBL) domain is a key adhesive module in Plasmodium falciparum, present in both erythrocyte invasion ligands (EBLs) and the large and diverse P. falciparum erythrocyte membrane protein 1 (PfEMP1) family of cytoadherence receptors. DBL domains bind a variety of different host receptors, including intercellular adhesion molecule 1 (ICAM-1), a receptor interaction that may have a role in infected erythrocyte binding to cerebral blood vessels and cerebral malaria. In this study, we expressed the nearly full complement of DBLbeta-C2 domains from the IT4/25/5 (IT4) parasite isolate and showed that ICAM-1-binding domains (DBLbeta-C2(ICAM-1)) were confined to group B and group C PfEMP1 proteins and were not present in group A, suggesting that ICAM-1 selection pressure differs between PfEMP1 groups. To further dissect the molecular determinants of binding, we modelled a DBLbeta-C2(ICAM-1) domain on a solved DBL structure and created alanine substitution mutants in two DBLbeta-C2(ICAM-1) domains. This analysis indicates that the DBLbeta-C2::ICAM-1 interaction maps to the equivalent glycan binding region of EBLs, and suggests a general model for how DBL domains evolve under dual selection for host receptor binding and immune evasion.     

Trichloroethylene exposure elicits damage in epididymal epithelium and spermatozoa in mice

We have investigated the toxic effects of trichloroethylene (TCE) on the epididymis and epididymal sperm in mice. Mice were exposed to TCE (1000 ppm) by inhalation for 6 h/day for 5 days/week for 1 to 4 weeks. Segments of the epididymis (caput, corpus and cauda) were examined by light and electron microscopy. At the light microscopic level, degeneration and sloughing of epithelial cells were evident as early as 1 week after TCE exposure, and were most pronounced after 4 weeks. Such epithelial damage was observed in the caput, corpus and cauda regions of the epididymis. Ultrastructural observations revealed vesiculation in the cytoplasm, disintegration of basolateral cell membranes, and sloughing of epithelial cells. Sperm were found in situ in the cytoplasm of degenerated epididymal cells. Additionally, a large number of sperm in the epididymal lumen exhibited abnormalities including malformation of head and tail components. Our results demonstrated that exposure to TCE by inhalation causes damage to the epididymal epithelium and sperm.