Spontaneous and pronase-induced HER2 truncation increases the trastuzumab binding capacity of breast cancer tissues and cell lines.

A subgroup of HER2-overexpressing breast tumours co-expresses p95(HER2), a truncated HER2 receptor that retains a functional HER2 kinase domain but lacks the extracellular domain, thus impairing trastuzumab binding. We evaluated p95(HER2) expression in 99 frozen breast carcinoma samples by western blot analysis. The HER2-positive cell line BT474 treated with pervanadate or pronase was used as a positive control for p95(HER2) expression. Immunohistochemistry was performed on parallel formalin-fixed, paraffin-embedded sections of the same case series using antibodies directed against either the intra- or extra-cellular binding domain of HER2. In particular, biotinylated trastuzumab (BiotHER) was used to evaluate the binding capacity of the humanized antibody. To avoid a subjective evaluation of the score values and the percentage of immunostained cells, the slides were scanned and automatically analysed. The number of cases with HER2 overexpression (score 3+) and HER2 gene amplification was higher in the p185(HER2)-positive/p95(HER2)-positive samples than in the p185(HER2)-positive/p95(HER2)-negative group. Automated analysis confirmed a significantly higher percentage of 3+ scored cells in p95(HER2)-positive cases. Conversely, the percentage of 2+ scored cells was higher inp95(HER2)-negative cases. The status of the HER2 extracellular domain was then studied using flow cytometry on BT474 cells after pronase enzymatic digestion using trastuzumab and pertuzumab, while the presence of HER2-HER3 dimers was studied using a proximity-ligation assay. In vitro experiments showed that short-term pronase digestion of BT474 cells produced two HER2 fragments (of 95 and 150 kDa, detectable in tissue specimens as well), increased the binding affinity of trastuzumab, reduced the rate of HER2-HER3 dimers, and did not interfere with pertuzumab-binding capacity. In conclusion, the presence of p95(HER2 as detected by western blot analysis does not compromise the immunohistochemical detection of HER2. Our data suggest that a reduction of the receptor steric hindrance as induced by enzymatic shedding may facilitate the binding capacity of trastuzumab.

A new antimicrobial peptide isolated from Oudneya africana seeds.

Oudneya africana R. Br. (Brassicaceae), a wild-growing plant in the arid region of Tunisia, is used in ethno-medicinal treatment of microbial infections. Validation of ethno-therapeutic claims pertaining to the plant was sought by investigating its antimicrobial activity. A proteinaceous extract of the seeds, called AS-3000, showed activity against various organisms including L. monocytogenes, E. coli, B. subtilis, E. hirae, P. aeruginosa, S. aureus and C. albicans. Extract AS-3000 exhibited a synergistic effect against L. ivanovii when combined with vancomycin or chloramphenicol. The post-antibiotic inhibitory effect of the ampicillin/AS-3000 combination was 2.3-fold greater than for the antibiotic alone. The mode of action of AS-3000 on Listeria and Escherichia was visible using SEM. These results support the use of O. africana for treating microbial infections.

A function for the AP3 coat complex in synaptic vesicle formation from endosomes.

Synaptic vesicles can be coated in vitro in a reaction that is ARF-, ATP-, and temperature-dependent and requires synaptic vesicle membrane proteins. The coat is largely made up of the heterotetrameric complex, adaptor protein 3, recently implicated in Golgi-to-vacuole traffic in yeast. Depletion of AP3 from brain cytosol inhibits small vesicle formation from PC12 endosomes in vitro. Budding from washed membranes can be reconstituted with purified AP3 and recombinant ARF1. We conclude that AP3 coating is involved in at least one pathway of small vesicle formation from endosomes.